Question 1. What Is The Main Difference Between Java Platform And Other Platforms?
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:
- Runtime Environment
- API(Application Programming Interface)
Question 2. When Abstract Methods Are Used?
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.
J2EE Interview Questions
Question 3. What Are Wrapper Classes?
These are classes that allow primitive types to be accessed as objects. Example: Integer, Character, Double, Boolean etc.
Question 4. What Do You Mean By Platform Independence?
Platform independence means 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).
Question 5. What Is A Pointer And Does Java Support Pointers?
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.
Core Java Interview Questions
Question 6. What Is The Difference Between Creating String As New() And Literal?
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. ( Deloitte JAVA interview questions )
Question 7. What Is The Use Of The Finally Block? Is Finally Block In Java Guaranteed To Be Called? When Finally Block Is Not Called?
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.
Core Java Tutorial JDBC Interview Questions
Question 8. What’s The Difference Between The Methods Sleep() And Wait()?
The code sleep(2000); puts thread aside for exactly two seconds. The code wait(2000), causes a wait of up to two second. A thread could stop waiting earlier if it receives the notify() or notifyAll() call. The method wait() is defined in the class Object and the method sleep() is defined in the class Thread.
Question 9. 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.
JSP Interview Questions
Question 10. Difference Between Final, Finally And Finalize ?
- 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.