Birlasoft Java Placement Papers - Birlasoft Java Interview Questions and Answers updated on 02.Mar.2024

If you want a class to contain a particular method but you want the actual implementation of that method to be determined by child classes, you can declare the method in the parent class as abstract.

Marker interface is an interface which help us to notify few information to JVM/Compiler. The marker interface does not have any body, it’s a empty interface. Ex. Cloneable, Serialization, etc.

Platform independence me that we can write and compile the java code in one platform (eg Windows) and can execute the class in any other supported platform eg (Linux,Solaris,etc).

Final is used to apply restrictions on class, method and variable. Final class can’t be inherited, final method can’t be overridden and final variable value can’t be changed.

Finally is used to place important code, it will be executed whether exception is handled or not.

Finalize is used to perform clean up processing just before object is garbage collected. Finalize is used to perform clean up processing just before object is garbage collected.

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.

When we create string with new() Operator, it’s created in heap and not added into string pool while String created using literal are created in String pool itself which exists in PermGen area of heap.

String s = new String(“Test”);

does not  put the object in String pool , we need to call String.intern() method which is used to put  them into String pool explicitly. its only when you create String object as String literal e.g. String s = “Test” Java automatically put that into String pool.

Basically it depends on the scenario , how you can handle. You need  handle this in dao layer, when doing insert operation you can call an utility method which will load the context ServletContextListener. Because, servlets are basically used for handling request and give the response.

The EJBContext interface provides an instance with access to the container-provided runtime context of an enterprise bean instance.

You need to do few tuning for this achievement. Few points below:                                                           

  1.   Use init() method for all expensive operation during  initialization (may be static data or cached data ).   
  2.   Always avoid auto loading of servlet.
  3.   Avoid SingleThreadModel.
  4.   Use and control HttpSession properly.

init() method is one of the life cycle method of servlet. This method runs once in total life. After servlet instance created and before it handles request the init() method will work. Its basically used for initializing values at the time of application startup.

Both are looks similar. But, the basic difference is abstract class can contain abstract and non abstract methods, where interface only contains abstract method (without method body). You can declare fields that are not static and final, and define public, protected, and private concrete methods in abstract class. But, in Interface all members are public, static and final , all methods are public.

These are classes that allow primitive types to be accessed as objects. Example: Integer, Character, Double, Boolean etc.

String, Integer ,Float ,etc. Basically all wrapper classed are final.

Garbage collection is a special feature in java language. It helps developer to save time and extra mental tension for handling object allocation in memory. It automatically clean the unused object from memory which helps to allocate space at runtime. When there is no reference to an object found, it will clean that object from memory . You can run the garbage collection explicitly by using System.gc().

Finally is the block of code that executes always. The code in finally block will execute even if an exception is occurred. Finally block is NOT called in following conditions

  • If the JVM exits while the try or catch code is being executed, then the finally block may not execute. This may happen due to System.exit() call.
  • if the thread executing the try or catch code is interrupted or killed, the finally block may not execute even though the application as a whole continues.
  • If a exception is thrown in finally block and not handled then remaining code in finally block may not be executed.

Pointer is a reference handle to a memory location. Improper handling of pointers leads to memory leaks and reliability issues hence Java doesn’t support the usage of pointers.

The Java platform differs from most other platforms in the sense that it’s a software-based platform that runs on top of other hardware-based platforms.

It has two components:

  1. Runtime Environment
  2. API(Application Programming Interface)

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