Java Interview Question and Answers

Tuesday, October 2, 2012

Questions : 1 What is JVM (Java Virtual Machine) ?
Answers : 1
JVM stands for Java Virtual Machine. It’s an abstract computer or virtual computer which runs the compiled java programs. Actually JVM is a software implementation which stands on the top of the real hardware platform and operating system. It provides abstraction between the compiled java program and the hardware and operating system. So the compiled program does not have to worry about what hardware and operating system he has to run in, it’s all handled by the JVM and thus attaining portability. All Java programs are compiled in to bytecodes. JVM can only understand and execute Java bytecodes. we can visualize Java bytecodes as machine language for JVM. Java compiler takes the .java files and compiles it to a “bytecode” file with .class file extension. Compiler generates one class file for one source file.
Questions : 2 What is JIT (Just-in-Time) Compilation ?
Answers : 2
When JVM compiles the class file he does not compile the full class file in one shot. Compilation is done on function basis or file basis. Advantage gained from this is that heavy parsing of original source code is avoided. Depending on need basis the compilation is done. This typ of compilation is termed as JIT or Just-in- Time compilation.
Questions : 3 How do you implement inheritance in Java?
Answers : 3
nheritance is implemented by using “EXTEND” keyword.


Sunday, March 11, 2012

Can an anonymous class be declared as implementing an interface and extending a class?
          An anonymous class may implement an interface or extend a superclass, but may not be declared to do both.

What is the range of the short type?
The range of the short type is -(2^15) to 2^15 - 1.

What is the range of the char type?
The range of the char type is 0 to 2^16 - 1.


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.

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.