Core Java

Core JAVA:

HashMap vs HashTable:

1. The HashMap class is roughly equivalent to Hashtable, except that it is non synchronized and permits nulls. (HashMap allows null values as key and value whereas Hashtable doesn't allow nulls).

2. HashMap does not guarantee that the order of the map will remain constant over time.

3. HashMap is non synchronized whereas Hashtable is synchronized.

4. Iterator in the HashMap is  fail-fast  while the enumerator for the Hashtable is not and throw ConcurrentModificationException if any other Thread modifies the map structurally  by adding or removing any element except Iterator's own remove()  method. But this is not a guaranteed behavior and will be done by JVM on best effort.

1)Synchronized means only one thread can modify a hash table at one point of time. Basically, it means that any thread before performing an update on a hashtable will have to acquire a lock on the object while others will wait for lock to be released.

2)Fail-safe is relevant from the context of iterators. If an iterator has been created on a collection object and some other thread tries to modify the collection object "structurally", a concurrent modification exception wjavascript:void(0)ill be thrown. It is possible for other threads though to invoke "set" method since it doesn't modify the collection "structurally". However, if prior to calling "set", the collection has been modified structurally, "IllegalArgumentException" will be thrown.

3)Structurally modification means deleting or inserting element which could effectively change the structure of map.

HashMap can be synchronized by

Map m = Collections.synchronizeMap(hashMap);

What is the difference between an Interface and an Abstract class?

An abstract class can have instance methods that implement a default behavior. An Interface can only declare constants and instance methods, but cannot implement default behavior and all methods are implicitly abstract. An interface has all public members and no implementation. An abstract class is a class which may have the usual flavors of class members (private, protected, etc.), but has some abstract methods.

Abstract:

is-a relation ship, hierarchical type, partial implementation

Interface:

can - do –this , common functionality, design appln

What is the purpose of garbage collection in Java, and when is it used?

                The purpose of garbage collection is to identify and discard objects that are no longer needed by a program so that their resources can be reclaimed and reused. A Java object is subject to garbage collection when it becomes unreachable to the program in which it is used.

Describe synchronization in respect to multithreading.

With respect to multithreading, synchronization is the capability to control the access of multiple threads to shared resources. Without synchonization, it is possible for one thread to modify a shared variable while another thread is in the process of using or updating same shared variable. This usually leads to significant errors.

Explain different way of using thread?

                The thread could be implemented by using runnable interface or by inheriting from the Thread class. The former is more advantageous, 'cause when you are going for multiple inheritance..the only interface can help.

Yield : will make thread to wait for the currently executing thread and the thread which has called yield() will attaches itself at the end of the thread execution. The thread which call yield() will be in Blocked state till its turn.

Sleep : will cause the thread to sleep in sleep mode for span of time mentioned in arguments.

Join : t1 and t2 are two threads , t2.join() is called then t1 enters into wait state until t2 completes execution. Then t1 will into runnable state then our specialist JVM thread scheduler will pick t1 based on criteria's.

Daemon thread:

Can make user thread to daemon to not to exit from jvm

1. Threads are easier to create than processes since they don't require a separate address space.

2. Multithreading requires careful programming since threads share data strucures that should only be modified by one thread at a time.  Unlike threads, processes don't share the same address space.

3.  Threads are considered lightweight because they use far less resources than processes.

4.  Processes are independent of each other.  Threads, since they share the same address space are interdependent, so caution must be taken so that different threads don't step on each other. 

5.  A process can consist of multiple threads.

Process:

An executing instance of a program is called a process.

Some operating systems use the term ‘task‘ to refer to a program that is being executed.

A process is always stored in the main memory also termed as the primary memory or random access memory.

Therefore, a process is termed as an active entity. It disappears if the machine is rebooted.

Several process may be associated with a same program.

On a multiprocessor system, multiple processes can be executed in parallel.

On a uni-processor system, though true parallelism is not achieved, a process scheduling algorithm is applied and the processor is scheduled to execute each process one at a time yielding an illusion of concurrency.

Example: Executing multiple instances of the ‘Calculator’ program. Each of the instances are termed as a process.

Thread:

A thread is a subset of the process.

It is termed as a ‘lightweight process’, since it is similar to a real process but executes within the context of a process and shares the same resources allotted to the process by the kernel (See kquest.co.cc/2010/03/operating-system for more info on the term ‘kernel’).

Usually, a process has only one thread of control – one set of machine instructions executing at a time.

A process may also be made up of multiple threads of execution that execute instructions concurrently.

Multiple threads of control can exploit the true parallelism possible on multiprocessor systems.

On a uni-processor system, a thread scheduling algorithm is applied and the processor is scheduled to run each thread one at a time.

All the threads running within a process share the same address space, file descriptors, stack and other process related attributes.

Since the threads of a process share the same memory, synchronizing the access to the shared data withing the process gains unprecedented importance.

Deadlock

Dead lock generally occurs  when 2 threads try to acquire same shared resource. In this case each thread end up waiting for other to release lock and deadlock occurs

Checked locking

How to find a deadlock scenario between two threads?

In theory deadlock can occur when more than one thread is competing for more than one common resource which are not synchronized properly.

Below is an example of two threads that are in a deadlock. We can see from the stack trace of the two threads (obtained from the thread dump) that thread with nid 0x6e8a has acquired a lock on the TransSession object and is waiting to lock VQLQuery object. While the other thread with nid 0xd8 has acquired a lock on VQLQuery object and is waiting to get a lock on TransSession object.

This is a deadlock scenario involving 2 resources and 2 threads. To recover from this scenario, the application has to be restarted OR there should be a mechanism to interrupt the threads. Hence, proper synchronized blocks should be used in the code to avoid deadlock scenarios.

 "ASYNC_ACTION_1214546556346" daemon prio=5 tid=0x0545f1a0 nid=0x6e8a waiting for monitor entry [0x79dfe000..0x79dffc28]
        at com.lucent.iems.platform.dm.datastore.datastorecache.CDataStoreCache.getNEDBObj(CDataStoreCache.java:171)
        - waiting to lock [0xa3c1cd50] (a com.versant.trans.VQLQuery)
        at com.lucent.iems.platform.dm.datastore.datastorecache.CDataStoreCache.replaceNEDHM(CDataStoreCache.java:435)
        - locked [0xa3c1cd68] (a com.versant.trans.TransSession)
        at com.lucent.iems.platform.dm.configmanager.dmconfig.CNEDataModelMgr.importNEinSession(CNEDataModelMgr.java:1088)
        at com.lucent.iems.platform.dm.configmanager.dmconfig.CNEDataModelMgr.importNE(CNEDataModelMgr.java:799)
        at com.lucent.iems.platform.dm.configmanager.dmconfig.CDMConfigEJB.importNE(CDMConfigEJB.java:2292)
        at com.lucent.iems.platform.dm.configmanager.dmconfig.CDMConfigEJB.importNE(CDMConfigEJB.java:2311)

 "TaskThread_45" daemon prio=5 tid=0x000dab00 nid=0xd8 waiting for monitor entry [0x7acdf000..0x7acdfc28]
        at com.versant.fund.SynchronizedCapi.executeVQL(SynchronizedCapi.java:547)
        - waiting to lock [0xa3c1cd68] (a com.versant.trans.TransSession)
        at com.versant.trans.TransSession.transExecuteVQL(TransSession.java:2961)
        at com.versant.trans.VQLQuery.execute(VQLQuery.java:114)
        at com.versant.trans.VQLQuery.execute(VQLQuery.java:94)
        at com.lucent.iems.platform.dm.datastore.datastorecache.necache.NECache.loadObject(NECache.java:55)        - locked [0xa3c1cd50] (a com.versant.trans.VQLQuery)
        at com.lucent.iems.platform.dm.datastore.datastorecache.Cache.getCacheObject(Cache.java:145)
        at com.lucent.iems.platform.dm.datastore.datastorecache.CDataStoreCache.getClassTable(CDataStoreCache.java:305)

What are pass by reference and passby value?

                Pass By Reference means the passing the address itself rather than passing the value. Passby Value means passing a copy of the value to be passed.

What is HashMap and Map?

                Map is Interface and Hashmap is class that implements that.

Difference between HashMap and HashTable?

                The HashMap class is roughly equivalent to Hashtable, except that it is unsynchronized and permits nulls. (HashMap allows null values as key and value whereas Hashtable doesnt allow). HashMap does not guarantee that the order of the map will remain constant over time. HashMap is unsynchronized and Hashtable is synchronized.

Difference between Vector and ArrayList?

                Vector is synchronized whereas arraylist is not.

Difference between Swing and Awt?

                AWT are heavy-weight componenets. Swings are light-weight components. Hence swing works faster than AWT.

What is the difference between a constructor and a method?

A constructor is a member function of a class that is used to create objects of that class. It has the same name as the class itself, has no return type, and is invoked using the new operator.

A method is an ordinary member function of a class. It has its own name, a return type (which may be void), and is invoked using the dot operator.

What is an Iterator?

                Some of the collection classes provide traversal of their contents via a java.util.Iterator interface. This interface allows you to walk through a collection of objects, operating on each object in turn. Remember when using Iterators that they contain a snapshot of the collection at the time the Iterator was obtained; generally it is not advisable to modify the collection itself while traversing an Iterator.

State the significance of public, private, protected, default modifiers both singly and in combination and state the effect of package relationships on declared items qualified by these modifiers.

public : Public class is visible in other packages, field is visible everywhere (class must be public too)

private : Private variables or methods may be used only by an instance of the same class that declares the variable or method, A private feature may only be accessed by the class that owns the feature.

protected : Is available to all classes in the same package and also available to all subclasses of the class that owns the protected feature.This access is provided even to subclasses that reside in a different package from the class that owns the protected feature.

default :What you get by default ie, without any access modifier (ie, public private or protected).It means that it is visible to all within a particular package.

What is an abstract class?

                 Abstract class must be extended/subclassed (to be useful). It serves as a template. A class that is abstract may not be instantiated (ie, you may not call its constructor), abstract class may contain static data. Any class with an abstract method is automatically abstract itself, and must be declared as such.

A class may be declared abstract even if it has no abstract methods. This prevents it from being instantiated.

What is static in java?

                Static means one per class, not one for each object no matter how many instance of a class might exist. This means that you can use them without creating an instance of a class.Static methods are implicitly final, because overriding is done based on the type of the object, and static methods are attached to a class, not an object. A static method in a superclass can be shadowed by another static method in a subclass, as long as the original method was not declared final. However, you can't override a static method with a nonstatic method. In other words, you can't change a static method into an instance method in a subclass.

What is final?

                A final class can't be extended ie., final class may not be subclassed. A final method can't be overridden when its class is inherited. You can't change value of a final variable (is a constant).

What if the main method is declared as private?

                 The program compiles properly but at runtime it will give "Main method not public." message.

What if the static modifier is removed from the signature of the main method?

                 Program compiles. But at runtime throws an error "NoSuchMethodError".

What if I write static public void instead of public static void?

                 Program compiles and runs properly.

What if I do not provide the String array as the argument to the method?

                 Program compiles but throws a runtime error "NoSuchMethodError".

What is the first argument of the String array in main method?

                 The String array is empty. It does not have any element. This is unlike C/C++ where the first element by default is the program name.

If I do not provide any arguments on the command line, then the String array of Main method will be empty or null?

                 It is empty. But not null.

How can one prove that the array is not null but empty using one line of code?

                 Print args.length. It will print 0. That means it is empty. But if it would have been null then it would have thrown a NullPointerException on attempting to print args.length.

What environment variables do I need to set on my machine in order to be able to run Java programs?

                 CLASSPATH and PATH are the two variables.

Can an application have multiple classes having main method?

                 Yes it is possible. While starting the application we mention the class name to be run. The JVM will look for the Main method only in the class whose name you have mentioned. Hence there is not conflict amongst the multiple classes having main method.

Can I have multiple main methods in the same class?

                 No the program fails to compile. The compiler says that the main method is already defined in the class.

Do I need to import java.lang package any time? Why ?

                 No. It is by default loaded internally by the JVM.

Can I import same package/class twice? Will the JVM load the package twice at runtime?

                 One can import the same package or same class multiple times. Neither compiler nor JVM complains abt it. And the JVM will internally load the class only once no matter how many times you import the same class.

What are Checked and UnChecked Exception?

A checked exception is some subclass of Exception (or Exception itself), excluding class RuntimeException and its subclasses.

Making an exception checked forces client programmers to deal with the possibility that the exception will be thrown. eg, IOException thrown by java.io.FileInputStream's read() method·

Unchecked exceptions are RuntimeException and any of its subclasses. Class Error and its subclasses also are unchecked. With an unchecked exception, however, the compiler doesn't force client programmers either to catch the exception or declare it in a throws clause. In fact, client programmers may not even know that the exception could be thrown. eg, StringIndexOutOfBoundsException thrown by String's charAt() method· Checked exceptions must be caught at compile time. Runtime exceptions do not need to be. Errors often cannot be.

What is Overriding?

When a class defines a method using the same name, return type, and arguments as a method in its superclass, the method in the class overrides the method in the superclass.

When the method is invoked for an object of the class, it is the new definition of the method that is called, and not the method definition from superclass. Methods may be overridden to be more public, not more private.

What are different types of inner classes?

                Nested top-level classes, Member classes, Local classes, Anonymous classes

Nested top-level classes- If you declare a class within a class and specify the static modifier, the compiler treats the class just like any other top-level class.

Any class outside the declaring class accesses the nested class with the declaring class name acting similarly to a package. eg, outer.inner. Top-level inner classes implicitly have access only to static variables.There can also be inner interfaces. All of these are of the nested top-level variety.

Member classes - Member inner classes are just like other member methods and member variables and access to the member class is restricted, just like methods and variables. This means a public member class acts similarly to a nested top-level class. The primary difference between member classes and nested top-level classes is that member classes have access to the specific instance of the enclosing class.

Local classes - Local classes are like local variables, specific to a block of code. Their visibility is only within the block of their declaration. In order for the class to be useful beyond the declaration block, it would need to implement a more publicly available interface.Because local classes are not members, the modifiers public, protected, private, and static are not usable.

Anonymous classes - Anonymous inner classes extend local inner classes one level further. As anonymous classes have no name, you cannot provide a constructor.

Are the imports checked for validity at compile time? e.g. will the code containing an import such as java.lang.ABCD compile?

 Yes the imports are checked for the semantic validity at compile time. The code containing above line of import will not compile. It will throw an error saying,can not resolve symbol

symbol : class ABCD

location: package io

import java.io.ABCD;

Does importing a package imports the subpackages as well? e.g. Does importing com.MyTest.* also import com.MyTest.UnitTests.*?

A:            No you will have to import the subpackages explicitly. Importing com.MyTest.* will import classes in the package MyTest only. It will not import any class in any of it's subpackage.

What is the difference between declaring a variable and defining a variable?

A:            In declaration we just mention the type of the variable and it's name. We do not initialize it. But defining means declaration + initialization.

e.g String s; is just a declaration while String s = new String ("abcd"); Or String s = "abcd"; are both definitions.

What is the default value of an object reference declared as an instance variable?

A:            null unless we define it explicitly.

Can a top level class be private or protected?

A:            No. A top level class can not be private or protected. It can have either "public" or no modifier. If it does not have a modifier it is supposed to have a default access.If a top level class is declared as private the compiler will complain that the "modifier private is not allowed here". This means that a top level class can not be private. Same is the case with protected.

What type of parameter passing does Java support?

A:            In Java the arguments are always passed by value .

Primitive data types are passed by reference or pass by value?

A:            Primitive data types are passed by value.

Objects are passed by value or by reference?

A:            Java only supports pass by value. With objects, the object reference itself is passed by value and so both the original reference and parameter copy both refer to the same object .

What is serialization?

A:            Serialization is a mechanism by which you can save the state of an object by converting it to a byte stream.

How do I serialize an object to a file?

A:            The class whose instances are to be serialized should implement an interface Serializable. Then you pass the instance to the ObjectOutputStream which is connected to a fileoutputstream. This will save the object to a file.

Which methods of Serializable interface should I implement?

                 The serializable interface is an empty interface, it does not contain any methods. So we do not implement any methods.

How can I customize the seralization process? i.e. how can one have a control over the serialization process?

                 Yes it is possible to have control over serialization process. The class should implement Externalizable interface. This interface contains two methods namely readExternal and writeExternal. You should implement these methods and write the logic for customizing the serialization process.

What is the common usage of serialization?

                 Whenever an object is to be sent over the network, objects need to be serialized. Moreover if the state of an object is to be saved, objects need to be serilazed.

What is Externalizable interface?

                 Externalizable is an interface which contains two methods readExternal and writeExternal. These methods give you a control over the serialization mechanism. Thus if your class implements this interface, you can customize the serialization process by implementing these methods.

When you serialize an object, what happens to the object references included in the object?

                 The serialization mechanism generates an object graph for serialization. Thus it determines whether the included object references are serializable or not. This is a recursive process. Thus when an object is serialized, all the included objects are also serialized alongwith the original obect.

What one should take care of while serializing the object?

                 One should make sure that all the included objects are also serializable. If any of the objects is not serializable then it throws a NotSerializableException.

What happens to the static fields of a class during serialization?

There are three exceptions in which serialization doesnot necessarily read and write to the stream. These are

1. Serialization ignores static fields, because they are not part of ay particular state state.

2. Base class fields are only hendled if the base class itself is serializable.

3. Transient fields.

Does Java provide any construct to find out the size of an object?

                 No there is not sizeof operator in Java. So there is not direct way to determine the size of an object directly in Java.

Give a simplest way to find out the time a method takes for execution without using any profiling tool?

                 Read the system time just before the method is invoked and immediately after method returns. Take the time difference, which will give you the time taken by a method for execution.

To put it in code...

long start = System.currentTimeMillis ();

method ();

long end = System.currentTimeMillis ();

System.out.println ("Time taken for execution is " + (end - start));

Remember that if the time taken for execution is too small, it might show that it is taking zero milliseconds for execution. Try it on a method which is big enough, in the sense the one which is doing considerable amout of processing.

What are wrapper classes?

                 Java provides specialized classes corresponding to each of the primitive data types. These are called wrapper classes. They are e.g. Integer, Character, Double etc.

Why do we need wrapper classes?

                 It is sometimes easier to deal with primitives as objects. Moreover most of the collection classes store objects and not primitive data types. And also the wrapper classes provide many utility methods also. Because of these resons we need wrapper classes. And since we create instances of these classes we can store them in any of the collection classes and pass them around as a collection. Also we can pass them around as method parameters where a method expects an object.

What are checked exceptions?

                 Checked exception are those which the Java compiler forces you to catch. e.g. IOException are checked Exceptions.

What are runtime exceptions?

                 Runtime exceptions are those exceptions that are thrown at runtime because of either wrong input data or because of wrong business logic etc. These are not checked by the compiler at compile time.

What is the difference between error and an exception?

                 An error is an irrecoverable condition occurring at runtime. Such as OutOfMemory error. These JVM errors and you can not repair them at runtime. While exceptions are conditions that occur because of bad input etc. e.g. FileNotFoundException will be thrown if the specified file does not exist. Or a NullPointerException will take place if you try using a null reference. In most of the cases it is possible to recover from an exception (probably by giving user a feedback for entering proper values etc.).

How to create custom exceptions?

                 Your class should extend class Exception, or some more specific type thereof.

If I want an object of my class to be thrown as an exception object, what should I do?

                 The class should extend from Exception class. Or you can extend your class from some more precise exception type also.

If my class already extends from some other class what should I do if I want an instance of my class to be thrown as an exception object?

                 One can not do anytihng in this scenarion. Because Java does not allow multiple inheritance and does not provide any exception interface as well.

How does an exception permeate through the code?

                 An unhandled exception moves up the method stack in search of a matching When an exception is thrown from a code which is wrapped in a try block followed by one or more catch blocks, a search is made for matching catch block. If a matching type is found then that block will be invoked. If a matching type is not found then the exception moves up the method stack and reaches the caller method. Same procedure is repeated if the caller method is included in a try catch block. This process continues until a catch block handling the appropriate type of exception is found. If it does not find such a block then finally the program terminates.

What are the different ways to handle exceptions?

                 There are two ways to handle exceptions,

1. By wrapping the desired code in a try block followed by a catch block to catch the exceptions. and

2. List the desired exceptions in the throws clause of the method and let the caller of the method hadle those exceptions.

               

What is the basic difference between the 2 approaches to exception handling.

1> try catch block and

2> specifying the candidate exceptions in the throws clause?

When should you use which approach?

                 In the first approach as a programmer of the method, you urself are dealing with the exception. This is fine if you are in a best position to decide should be done in case of an exception. Whereas if it is not the responsibility of the method to deal with it's own exceptions, then do not use this approach. In this case use the second approach. In the second approach we are forcing the caller of the method to catch the exceptions, that the method is likely to throw. This is often the approach library creators use. They list the exception in the throws clause and we must catch them. You will find the same approach throughout the java libraries we use.

Is it necessary that each try block must be followed by a catch block?

                 It is not necessary that each try block must be followed by a catch block. It should be followed by either a catch block OR a finally block. And whatever exceptions are likely to be thrown should be declared in the throws clause of the method.

If I write return at the end of the try block, will the finally block still execute?

                 Yes even if you write return as the last statement in the try block and no exception occurs, the finally block will execute. The finally block will execute and then the control return.

If I write System.exit (0); at the end of the try block, will the finally block still execute?

                 No in this case the finally block will not execute because when you say System.exit (0); the control immediately goes out of the program, and thus finally never executes.

How are Observer and Observable used?

                 Objects that subclass the Observable class maintain a list of observers. When an Observable object is updated it invokes the update() method of each of its observers to notify the observers that it has changed state. The Observer interface is implemented by objects that observe Observable objects.

What is synchronization and why is it important?

                 With respect to multithreading, synchronization is the capability to control

the access of multiple threads to shared resources. Without synchronization, it is possible for one thread to modify a shared object while another thread is in the process of using or updating that object's value. This often leads to significant errors.

How does Java handle integer overflows and underflows?

                 It uses those low order bytes of the result that can fit into the size of the type allowed by the operation.

Does garbage collection guarantee that a program will not run out of memory?

                 Garbage collection does not guarantee that a program will not run out of memory. It is possible for programs to use up memory resources faster than they are garbage collected. It is also possible for programs to create objects that are not subject to garbage collection

What is the difference between preemptive scheduling and time slicing?

                 Under preemptive scheduling, the highest priority task executes until it enters the waiting or dead states or a higher priority task comes into existence. Under time slicing, a task executes for a predefined slice of time and then reenters the pool of ready tasks. The scheduler then determines which task should execute next, based on priority and other factors.

When a thread is created and started, what is its initial state?

                 A thread is in the ready state after it has been created and started.

What is the purpose of finalization?

                 The purpose of finalization is to give an unreachable object the opportunity to perform any cleanup processing before the object is garbage collected.

What is the Locale class?

                 The Locale class is used to tailor program output to the conventions of a particular geographic, political, or cultural region.

What is the difference between a while statement and a do statement?

                 A while statement checks at the beginning of a loop to see whether the next loop iteration should occur. A do statement checks at the end of a loop to see whether the next iteration of a loop should occur. The do statement will always execute the body of a loop at least once.

What is the difference between static and non-static variables?

                 A static variable is associated with the class as a whole rather than with specific instances of a class. Non-static variables take on unique values with each object instance.

How are this() and super() used with constructors?

                 This() is used to invoke a constructor of the same class. super() is used to invoke a superclass constructor.

What are synchronized methods and synchronized statements?

                 Synchronized methods are methods that are used to control access to an object. A thread only executes a synchronized method after it has acquired the lock for the method's object or class. Synchronized statements are similar to synchronized methods. A synchronized statement can only be

What is daemon thread and which method is used to create the daemon thread?

                 Daemon thread is a low priority thread which runs intermittently in the back ground doing the garbage collection operation for the java runtime system. setDaemon method is used to create a daemon thread.

Can applets communicate with each other?

                 At this point in time applets may communicate with other applets running in the same virtual machine. If the applets are of the same class, they can communicate via shared static variables. If the applets are of different classes, then each will need a reference to the same class with static variables. In any case the basic idea is to pass the information back and forth through a static variable.

An applet can also get references to all other applets on the same page using the getApplets() method of java.applet.AppletContext. Once you get the reference to an applet, you can communicate with it by using its public members.

It is conceivable to have applets in different virtual machines that talk to a server somewhere on the Internet and store any data that needs to be serialized there. Then, when another applet needs this data, it could connect to this same server. Implementing this is non-trivial.

What are the steps in the JDBC connection?

                  While making a JDBC connection we go through the following steps :

Step 1 : Register the database driver by using :

Class.forName(\" driver classs for that specific database\" );

Step 2 : Now create a database connection using :

Connection con = DriverManager.getConnection(url,username,password);

Step 3: Now Create a query using :

Statement stmt = Connection.Statement(\"select * from TABLE NAME\");

Step 4 : Exceute the query :

stmt.exceuteUpdate();

How does a try statement determine which catch clause should be used to handle an exception?

When an exception is thrown within the body of a try statement, the catch clauses of the try statement are examined in the order in which they appear. The first catch clause that is capable of handling the exceptionis executed. The remaining catch clauses are ignored.

Can an unreachable object become reachable again?

                 An unreachable object may become reachable again. This can happen when the object's finalize() method is invoked and the object performs an operation which causes it to become accessible to reachable objects.

What method must be implemented by all threads?

                 All tasks must implement the run() method, whether they are a subclass of Thread or implement the Runnable interface.

What are synchronized methods and synchronized statements?

                 Synchronized methods are methods that are used to control access to an object. A thread only executes a synchronized method after it has acquired the lock for the method's object or class. Synchronized statements are similar to synchronized methods. A synchronized statement can only be executed after a thread has acquired the lock for the object or class referenced in the synchronized statement.

What is Externalizable?

                 Externalizable is an Interface that extends Serializable Interface. And sends data into Streams in Compressed Format. It has two methods, writeExternal(ObjectOuput out) and readExternal(ObjectInput in)

What modifiers are allowed for methods in an Interface?

                 Only public and abstract modifiers are allowed for methods in interfaces.

What are some alternatives to inheritance?

                 Delegation is an alternative to inheritance. Delegation means that you include an instance of another class as an instance variable, and forward messages to the instance. It is often safer than inheritance because it forces you to think about each message you forward, because the instance is of a known class, rather than a new class, and because it doesn't force you to accept all the methods of the super class: you can provide only the methods that really make sense. On the other hand, it makes you write more code, and it is harder to re-use (because it is not a subclass).

What does it mean that a method or field is "static"?

                 Static variables and methods are instantiated only once per class. In other words they are class variables, not instance variables. If you change the value of a static variable in a particular object, the value of that variable changes for all instances of that class.

Static methods can be referenced with the name of the class rather than the name of a particular object of the class (though that works too). That's how library methods like System.out.println() work out is a static field in the java.lang.System class.

What is the difference between preemptive scheduling and time slicing?

                 Under preemptive scheduling, the highest priority task executes until it enters the waiting or dead states or a higher priority task comes into existence. Under time slicing, a task executes for a predefined slice of time and then reenters the pool of ready tasks. The scheduler then determines which task should execute next, based on priority and other factors.

What is the catch or declare rule for method declarations?

                 If a checked exception may be thrown within the body of a method, the method must either catch the exception or declare it in its throws clause.

Is Empty .java file a valid source file?

                 Yes, an empty .java file is a perfectly valid source file.

Can a .java file contain more than one java classes?

                Yes, a .java file contain more than one java classes, provided at the most one of them is a public class.

Is String a primitive data type in Java?

                 No String is not a primitive data type in Java, even though it is one of the most extensively used object. Strings in Java are instances of String class defined in java.lang package.

Is main a keyword in Java?

                 No, main is not a keyword in Java.

Is next a keyword in Java?

                 No, next is not a keyword.

Is delete a keyword in Java?

                 No, delete is not a keyword in Java. Java does not make use of explicit destructors the way C++ does.

Is exit a keyword in Java?

                 No. To exit a program explicitly you use exit method in System object.

What happens if you dont initialize an instance variable of any of the primitive types in Java?

                 Java by default initializes it to the default value for that primitive type. Thus an int will be

What will be the initial value of an object reference which is defined as an instance variable?

                 The object references are all initialized to null in Java. However in order to do anything useful with these references, you must set them to a valid object, else you will get NullPointerExceptions everywhere you try to use such default initialized references.

What are the different scopes for Java variables?

                 The scope of a Java variable is determined by the context in which the variable is declared. Thus a java variable can have one of the three scopes at any given point in time.

1. Instance : - These are typical object level variables, they are initialized to default values at the time of creation of object, and remain accessible as long as the object accessible.

2. Local : - These are the variables that are defined within a method. They remain accessbile only during the course of method excecution. When the method finishes execution, these variables fall out of scope.

3. Static: - These are the class level variables. They are initialized when the class is loaded in JVM for the first time and remain there as long as the class remains loaded. They are not tied to any particular object instance.

What is the default value of the local variables?

                 The local variables are not initialized to any default value, neither primitives nor object references. If you try to use these variables without initializing them explicitly, the java compiler will not compile the code. It will complain abt the local varaible not being initilized..

How many objects are created in the following piece of code?

MyClass c1, c2, c3;

c1 = new MyClass ();

c3 = new MyClass ();

                 Only 2 objects are created, c1 and c3. The reference c2 is only declared and not initialized.

Can a public class MyClass be defined in a source file named YourClass.java?

                No the source file name, if it contains a public class, must be the same as the public class name itself with a .java extension.

Can main method be declared final?

What will be the output of the following statement?

System.out.println ("1" + 3);

                 It will print 13.

What will be the default values of all the elements of an array defined as an instance variable?

                If the array is an array of primitive types, then all the elements of the array will be initialized to the default value corresponding to that primitive type. e.g. All the elements of an array of int will be initialized to 0, while that of boolean type will be initialized to false. Whereas if the array is an array of references (of any type), all the elements will be initialized to null.

Collections:

What is the Collections API?

                The Collections API is a set of classes and interfaces that support operations on collections of objects.

What is the List interface?

                The List interface provides support for ordered collections of objects.

What is the Vector class?

                The Vector class provides the capability to implement a growable array of objects.

What is an Iterator interface?

                The Iterator interface is used to step through the elements of a Collection .

Which java.util classes and interfaces support event handling?

                The EventObject class and the EventListener interface support event processing.

What is the GregorianCalendar class?

                The GregorianCalendar provides support for traditional Western calendars

What is the Locale class?

                The Locale class is used to tailor program output to the conventions of a particular geographic, political, or cultural region .

What is the SimpleTimeZone class?

                The SimpleTimeZone class provides support for a Gregorian calendar .

What is the Map interface?

                The Map interface replaces the JDK 1.1 Dictionary class and is used associate keys with values.

What is the highest-level event class of the event-delegation model?

                The java.util.EventObject class is the highest-level class in the event-delegation class hierarchy.

What is the Collection interface?

                The Collection interface provides support for the implementation of a mathematical bag - an unordered collection of objects that may contain duplicates.

What is the Set interface?

                The Set interface provides methods for accessing the elements of a finite mathematical set. Sets do not allow duplicate elements.

What is the typical use of Hashtable?

                 Whenever a program wants to store a key value pair, one can use Hashtable.

I am trying to store an object using a key in a Hashtable. And some other object already exists in that location, then what will happen? The existing object will be overwritten? Or the new object will be stored elsewhere?

                The existing object will be overwritten and thus it will be lost.

What is the difference between the size and capacity of a Vector?

                The size is the number of elements actually stored in the vector, while capacity is the maximum number of elements it can store at a given instance of time.

Can a vector contain heterogenous objects?

                Yes a Vector can contain heterogenous objects. Because a Vector stores everything in terms of Object.

Can a ArrayList contain heterogenous objects?

                Yes a ArrayList can contain heterogenous objects. Because a ArrayList stores everything in terms of Object.

What is an enumeration?

                 An enumeration is an interface containing methods for accessing the underlying data structure from which the enumeration is obtained. It is a construct which collection classes return when you request a collection of all the objects stored in the collection. It allows sequential access to all the elements stored in the collection.

Considering the basic properties of Vector and ArrayList, where will you use Vector and where will you use ArrayList?

                The basic difference between a Vector and an ArrayList is that, vector is synchronized while ArrayList is not. Thus whenever there is a possibility of multiple threads accessing the same instance, one should use Vector. While if not multiple threads are going to access the same instance then use ArrayList. Non synchronized data structure will give better performance than the synchronized one.

throws  vs throw

throws:handles multiple exception

throw:handles single exception

stack  vs heap

stack allocates memory for local variables / method

heap allocates memory for objects

ejb life cycle

ejbactive,ejb passivate,does not exist, method pool

Exception handling

                     Throwable

Exception                                    Error         

RuntimeException       

IOException                          NoClassFoundException

CompileTimeException          AssertionError

                                             OutOfMemoryException

1) Checked Exception is required to be handled by compile time while Unchecked Exception doesn't.

2) Checked Exception is direct sub-Class of Exception while Unchecked Exception are of RuntimeException.

3) CheckedException represent scenario with higher failure rate while UnCheckedException are mostly programming mistakes.

Sorting algorithm for minimum complexity: O(n*log(n))

Overriding - Dynamic binding - Run time pmorphism:

Same method name and same return type and same arguments

Overloading - Static binding - Compile time pmorphism:

Different method name and same return type and different arguments

String:

1.       ==  checks if types are same

2.       equals checks value of object is same

String is immutable

StringBuffer is mutable

StringBuffer and StringBuilder have the same methods with one difference and that’s of synchronization. StringBuffer is synchronized( which means it is thread safe and hence you can use it when you implement threads for your methods) whereas StringBuilder is not synchronized( which implies it isn’t thread safe).So, if you aren’t going to use threading then use the StringBuilder class as it’ll be more efficient than StringBuffer due to the absence of  synchronization.

When to use a Factory Pattern?

The Factory patterns can be used in following cases:

1. When a class does not know which class of objects it must create.

2. A class specifies its sub-classes to specify which objects to create.

3. In programmer’s language (very raw form), you can use factory pattern where you have to create an object of any one of sub-classes depending on the data provided.

http://weblogs.java.net/blog/2006/05/04/understanding-weak-references

Reference in java:

strong ref--- new A();can't collect by garbage

soft reference:

object destruction will stick for while and better than weak ref.

weak reference --- new A(String str);

immediately collected by garbage.

phantom reference: override finalize and collect garbage values

Types of design pattern:

Creational

Factory, Singleton

 Structural

Façade, behavioral, Interceptor

ArrayList synchronization:

Collections.synchronizedList(list)

CopyOnWriteArrayList

Vector:

set capacity and increment by manually

real time: user comments in key post for only 5 times

HashTable:

by default descending order

TreeSet and TreeMap

by default ascending order

HashMap and HashSet

by default random wise

Vector

Synchronized,slower as compare to arraylist,mostly use with single threading,allow null value,allow duplicate

Array List

Non-Synchronized, Faster, multi threading, allow null value, allow duplicate

Reflection :--- Object.getClass().getMethod();

http://www.mkyong.com/java/how-to-use-reflection-to-call-java-method-at-runtime/

http://viralpatel.net/blogs/java-dynamic-class-loading-java-reflection-api/

package com.test;

import java.lang.reflect.InvocationTargetException;

import java.lang.reflect.Method;

public class Reflection {

    public Reflection() {

    }

    public void printData(String msg,Integer i) {

        System.out.println("Msg: " + msg+" Count:"+ i);

    }

}

class RefTest {

    public static void main(String[] args) {

try {

    ClassLoader cl=ClassLoader.getSystemClassLoader();

    Class cls=cl.loadClass("com.test.Reflection");

    Object o=cls.newInstance();

    Method m=cls.getMethod("printData", new Class[]{ String.class,Integer.class});

    m.invoke(o, "hi bh",8);

} catch (InstantiationException e) {

    e.printStackTrace();

} catch (IllegalAccessException e) {

    e.printStackTrace();

} catch (SecurityException e) {

    e.printStackTrace();

} catch (ClassNotFoundException e) {

    e.printStackTrace();

} catch (NoSuchMethodException e) {

    e.printStackTrace();

} catch (IllegalArgumentException e) {

    e.printStackTrace();

} catch (InvocationTargetException e) {

    e.printStackTrace();

}    } }

Design pattern

 Design Pattern is a solution to a rather localized problem - like "how can several classes share and customize a basic algorithm" -> Template Method.
- an Architectural Pattern is a solution to a rather global problem and therefore often more abstract than a Design Pattern - like "how can I shape the system, so that changes in the UI don't affect the model" -> MVC

Architectural pattern

MVC is an 'Architecture' to which the code is separated into 3 different responsibilities (Model-View-Controller). In general I define an Architecture as the overall assembly and organization of the code (MVC, MVP, 3-layer UI-BLL-DAL, Domain Model, MVVM, etc). This is typically a decision made at the onset of the application's creation and not quite easy to change once implementation has occurred (not impossible but difficult to switch say a 'traditional 3 layer' app to 'MVC).

A 'Design Pattern' is an element of reusable code (yep from the original book...) and typically design patterns can be implemented 1...n all throughout the code where needed and useful. You might have 5-10 different implementations of different design patterns for certain classes or groupings of classes within a traditional 3-layer application. For example, you might have instances of the Factory Method, Singleton, Strategy, State, and Composite design patterns all implemented within your main application. However you might still be adhering to an overall single architecture (or possibly a combination depending on the application, technologies used (i.e. Silverlight + ASP.NET), history, use, and so on).

Why Frameworks (Framework features)

Design patterns say how to write code effectively (considering Code Metrics).

A few benefits:

Easily Maintainable
High Re-usability
Readable because of abstractions
Architectural patterns say how to utilize resources effectively.

Parallel tasks execution like programmers and graphic designers can work parallel.
Multiple technologies can be utilized to build a software.

Spring 

IOC

Setter constructor injection

Autowire

JDBC Template

Tasks scheduler

MVC

ModelAttribute and ModelView

Spring tags

Hibernate

Fisrt level Cache: Default

Second level cahce:EH cache

-read only, read-write forcibly, read and write, transactions

Multiple database connections

Mapping

AngularJS Controller implementing

Database

views 

joins

primary key: one for table

unique key:contains one null

composite key:one or more column

foreign key:primary key acts as foreign key, referncing other table

ddl:create,alter,drop

dml:update,insert,delete

tcl:commit,rollback

prepared statement

Connection pooling

MultiThread

Runnable, Callable

run vs call method

Executor vs Executors vs ExecutorService

hashCode, equals

Externalizable extends Serializable(Marker interface(indicates jvm compiler)- no methods)

readExternal,writeExternal

Hibernate:

Reduces boiler plate code(same code in many places)

Lazy initialization uses proxy objects, so whenever required it will query to DB

HQL is object oriented query language

Exception handling and transaction management(commit, rollback)

Sophisticated cache inbuilt mechnaism while JDBC has to be done in manually

opensession- opens new session and needs to be closesession

getCurrentSession- returns session object, no need to close.get closed when automatically SessionFactory object get closed

Session Management:

HttpSession session=req.getSession();

Cookies = new Cookies("user",session)

request.getCoookies("user")

URLRewiting:

// Encode a URL string with the session id appended

  // to it.

  String url = response.encodeRedirectURL(

   "http://localhost:8000/servlet/checkout?sid=5748");

  // Redirect the client to the new URL

  response.sendRedirect(url);

  Object Creation types:

  1.Object o=new Object();

  2.MyObject object = (MyObject) Class.forName("subin.rnd.MyObject").newInstance();

  3.MyObject anotherObject = new MyObject();

  MyObject object = (MyObject) anotherObject.clone();

4.ObjectInputStream inStream = new ObjectInputStream(anInputStream );

MyObject object = (MyObject) inStream.readObject();

Java Reflection is a process of examining or modifying the run time behavior of a class at run time.

The java.lang.Class class provides many methods that can be used to get metadata, examine and change the run time behavior of a class.

The java.lang and java.lang.reflect packages provide classes for java reflection.

Where it is used

The Reflection API is mainly used in:

IDE (Integrated Development Environment) e.g. Eclipse, MyEclipse, NetBeans etc.

Debugger

Test Tools etc.

Reflection is a language's ability to inspect and dynamically call classes, methods, attributes, etc. at runtime

List iterator vs Iterator:

 Methods of Iterator:

hasNext()

next()

remove()

Methods of ListIterator:

add(E e)

hasNext()

hasPrevious()

next()

nextIndex()

previous()

previousIndex()

remove()

set(E e)

Enumeration is legacy Iterator and Enum is a data type. Enums are instance controlled classes in java. ... While Enumeration was the old way to iterate through a collection. It has two methods nextElement and hasMoreElements which are more like next and hasNext methods of Iterator interface.

fail-fast iterator fails by throwing a ConcurrentModificationException.

Fail-safe is weakly consistent and Collection objects can be modified

Iterator of CopyOnWriteArrayList is an example of fail-safe Iterator also iterator written by ConcurrentHashMap keySet is also fail-safe iterator and never throw ConcurrentModificationException in Java.

ail Fast Vs Fail Safe Iterators In Java :

Fail-Fast Iterators Fail-Safe Iterators

Fail-Fast iterators doesn’t allow modifications of a collection while iterating over it. Fail-Safe iterators allow modifications of a collection while iterating over it.

These iterators throw ConcurrentModificationException if a collection is modified while iterating over it. These iterators don’t throw any exceptions if a collection is modified while iterating over it.

They use original collection to traverse over the elements of the collection. They use copy of the original collection to traverse over the elements of the collection.

These iterators don’t require extra memory. These iterators require extra memory to clone the collection.

Ex : Iterators returned by ArrayList, Vector, HashMap. Ex : Iterator returned by ConcurrentHashMap.

Unchecked Exception List

ArrayIndexOutOfBoundsException

ClassCastException

IllegalArgumentException

IllegalStateException

NullPointerException

NumberFormatException

AssertionError

ExceptionInInitializerError

StackOverflowError

NoClassDefFoundError

Checked Exception List

Exception

IOException

FileNotFoundException

ParseException

ClassNotFoundException

CloneNotSupportedException

InstantiationException

InterruptedException

NoSuchMethodException

NoSuchFieldException

Declaring a variable as volatile means that modifying its value immediately affects the actual memory storage for the variable. The compiler cannot optimize away any references made to the variable. This guarantees that when one thread modifies the variable, all other threads see the new value immediately. (This is not guaranteed for non-volatile variables.)

Declaring an atomic variable guarantees that operations made on the variable occur in an atomic fashion, i.e., that all of the substeps of the operation are completed within the thread they are executed and are not interrupted by other threads. For example, an increment-and-test operation requires the variable to be incremented and then compared to another value; an atomic operation guarantees that both of these steps will be completed as if they were a single indivisible/uninterruptible operation.

Synchronizing all accesses to a variable allows only a single thread at a time to access the variable, and forces all other threads to wait for that accessing thread to release its access to the variable.

Synchronized access is similar to atomic access, but the atomic operations are generally implemented at a lower level of programming. Also, it is entirely possible to synchronize only some accesses to a variable and allow other accesses to be unsynchronized (e.g., synchronize all writes to a variable but none of the reads from it).

The peek() method is used to look at the object at the top of this stack without removing it from the stack.

import java.util.*;

public class StackDemo {

   public static void main(String args[]) {

   // creating stack

   Stack st = new Stack();

      

   // populating stack

   st.push("Java");

   st.push("Source");

   st.push("code");

      

   // checking the top object

   System.out.println("Top object is: "+st.peek());

   }     

}

O/P: code

import java.util.*;

public class PriorityQueueDemo {

   public static void main(String args[]) {

   // create priority queue

   PriorityQueue < Integer >  prq = new PriorityQueue < Integer > (); 

       

   // insert values in the queue

   for ( int i = 3; i  <  10; i++ ){  

   prq.add (new Integer (i)) ; 

   }

      

   System.out.println ( "Initial priority queue values are: "+ prq);

      

   // get the head from the queue

   Integer head = prq.poll();

      

   System.out.println ( "Head of the queue is: "+ head);

      

   System.out.println ( "Priority queue values after poll: "+ prq);

   }

}

O/P:

Initial priority queue values are: [3, 4, 5, 6, 7, 8, 9]

Head of the queue is: 3

Priority queue values after poll: [4, 6, 5, 9, 7, 8]

1. Criteria basic query

Create a criteria object and retrieve all the ‘StockDailyRecord’ records from database.

Criteria criteria = session.createCriteria(StockDailyRecord.class);

2. Criteria ordering query

The result is sort by ‘date’ in ascending order.

Criteria criteria = session.createCriteria(StockDailyRecord.class)

    .addOrder( Order.asc("date") );

The result is sort by ‘date’ in descending order.

Criteria criteria = session.createCriteria(StockDailyRecord.class)

    .addOrder( Order.desc("date") );

3. Criteria restrictions query

The Restrictions class provide many methods to do the comparison operation.

Restrictions.eq, Restrictions.lt, Restrictions.gt, Restrictions.ge,Restrictions.like, Restrictions.between

Make sure the valume is equal to 10000.

Criteria criteria = session.createCriteria(StockDailyRecord.class)

    .add(Restrictions.eq("volume", 10000));

REGEX

-----

Pattern and Matcher class

java.util.regex package primarily consists of the following three classes −

Pattern Class − A Pattern object is a compiled representation of a regular expression. The Pattern class provides no public constructors. To create a pattern, you must first invoke one of its public static compile() methods, which will then return a Pattern object. These methods accept a regular expression as the first argument.

Matcher Class − A Matcher object is the engine that interprets the pattern and performs match operations against an input string. Like the Pattern class, Matcher defines no public constructors. You obtain a Matcher object by invoking the matcher() method on a Pattern object.

This is individual contributor role

 -Take handover from vendors based globally and in-source work

 -Take E2E Accountability and ownership of work/projects and execute projects using AGILE methodology

 -Understanding of risk business and Architecture

 -Converting business requirements into technical design

 -Development on key strategic risk platform using SDLC methodologies like Waterfall/Iterative/AGILE

 -Delivery, Deployment, Review, Business interaction and Maintaining environments

 -Contribute to Pune tech. center build out and be part of COP 

 Key Tasks:

 -Participates in design sessions and contribute to robust design

 -Contributes and adheres to the definition of development and SW standards to implement/reflect DB guidelines (naming conventions, encryption, and security settings) 

 -Ensures architectural changes (as defined by Architects) are implemented

 -Develops source code, including descriptions, for all software Components in accordance with Detailed Software Requirements specification, the functional design and the technical design document or backlog

 -Participates and guides others for code reviews

 -Integrates software components following the groups integration strategy

 -Verifies integrated software components by unit and integrated software testing according to the software test plan. Software test findings must be resolved

 -Ensures that all code changes are tracked and recorded through the groups change management process and that development is scheduled and approved

 -Provides Release Deployments on non-Production Management controlled environments

 -Capture Build and Deployment notes, develop Software Product Deployment & Operating Instructions

 -Provides Level 3 support for technical infrastructure components (i.e., databases, middleware and user interfaces)

 -Contributes to root cause /problem analysis

 -Fixes software defects/bugs and responsible for code quality and ensure zero-defect in their code

 -Collaborates with Functional Analysts and technical Specialists to complete work, as required

 -Develops mathematical calculations which perform to expected results and handle negative test case scenarios

 

Responsibilities

•Does implementation of key modules and can develop quick working prototypes, when necessary

•Does component module/ sub- system design

•Responsible for “code quality” through design and code reviews

•Identifying and resolving technical risks

•Guide team members in developing modules

•Supports in estimation, planning and risk management activities

•Contribute to the decomposition of work items into consumable units

•Manage technical communication with customers

•To keep abreast of technical & organizational developments in own professional field.

Role Competency:

•Experience in web services/technologies and scripts

•Experience in developing applications in Java

•Experience in leading team members in application development (for seniors)

•Experience in developing applications using Agile/SAFe

•Working with multisite teams, Quality conscious and Process Oriented

•Experience in Spring MVC, Angular, Hibernate would be a value add

Personal Characteristics

•Communication skills: excellent oral and written skills

•Self-starter and quick learner and ability to work in a global team setting with minimal supervision

•Highly productive and flexible to take additional responsibilities.

•Should be a good team player.

static variable declared in parent class is accessible in child class

cascade vs inverse - hibernate

Multithreading is used mostly in banking domain.Learn concurrent package in multithreading.

Following are the important topic to be covered in concurrent package:

ExecutorService

ThreadPoolExecutor

CountDownLatch

CyclicBarrier

BlockingQueue

ForkJoinPool

hibernate with multiple databse connections

databse views

spring autowire

spring getting particular reference(ex:from emp1, emp2 get emp2 ref)

xml request ot REST

lamda expression in java8

Restcontroller vs controller

reflection

finalize

shutdown hook [when out of memory]

thread join

thread yield

wait notify notifyAll

thread synchronisation vs immutable

synchronize method -bank transactions vs synchronize block -login method

arraylist internal strucutre

queue=linked list

spring mvc

spring batch

tasklet vs step

java8 features

thread memory sharing/access

factory pattern-scenario-passing object to remote lab machine

thread life cycle

spring batch

hibernate load and get

spring orm vs hibernate

spring jdbc, spring dao,

spring boot

hibernate first level, second level cache

hibernate steps to connect db

queue, linked list

java8 features

design patterns

factory pattern

semaphore 

mutex

checked exception:

compile time

ex:add trhows or surround try.catch block

unchecked exception:

runtime

arrayindexoutof bounds exception

Error and RuntimeException

hibernate session

garbage collection automatic or manual

remove last third nodes

encapsulation 

overriding

abstraction

jre exception class

how not to handle exception

&& & || | operator

abstract class be final

inner class in interface

main method be final

autoboxing, unboxing

how many concrete classes inside an interface 

gsmwatcherscenario--available()-->gsmmodel-locked

gsmwatcherscenario--getkey()-->gsmmodel

RDBMS

sql ddl,dml

sql column resize

sql add of salary

sql add of salary at 15% hike

sql subquery

sql joins

sql orderby sorting

•Coding, Compiling, Unit testing, packaging and deployment of developed software.

•Works on periodic maintenance releases of applications, including enhancements and defects.

•Responsible for development, support, maintenance and implementation of analytic module.

•Presentation Layer (JSP/Servlet), Databases, Build and Release, Systems Integration, Agile, Estimations/Planning, OOPS Concepts, Client Management/Interaction.