1. What is the most important feature of Java?
Java is a platform independent language.
2. 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).
3. What is a JVM?
JVM is Java Virtual Machine which is a run time environment for the compiled java
4. Are JVM’s platform independent?
JVM’s are not platform independent. JVM’s are platform specific run time
implementation provided by the vendor.
5. What is the difference between a JDK and a JVM?
JDK is Java Development Kit which is for development purpose and it includes
execution environment also. But JVM is purely a run time environment and
hence you will not be able to compile your source files using a JVM.
6. 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.
7. What is the base class of all classes?
8. Does Java support multiple inheritance?
Java doesn’t support multiple inheritance.
9. Is Java a pure object oriented language?
Java uses primitive data types and hence is not a pure object oriented language.
10. Are arrays primitive data types?
In Java, Arrays are objects.
11. What is difference between Path and Classpath?
Path and Classpath are operating system level environment variales. Path is used
define where the system can find the executables(.exe) files and classpath is
used to specify the location .class files.
12. What are local variables?
Local varaiables are those which are declared within a block of code like methods.
Local variables should be initialised before accessing them.
13. What are instance variables?
Instance variables are those which are defined at the class level. Instance
variables need not be initialized before using them as they are automatically
initialized to their default values.
14. How to define a constant variable in Java?
The variable should be declared as static and final. So only one copy of the
variable exists for all instances of the class and the value can’t be changed also.
static final int PI = 3.14; is an example for constant.
15. Should a main() method be compulsorily declared in all java classes?
No not required. main() method should be defined only if the source class is a
16. What is the return type of the main() method?
Main() method doesn’t return anything hence declared void.
17. Why is the main() method declared static?
main() method is called by the JVM even before the instantiation of the class
hence it is declared as static.
18. What is the argument of main() method?
main() method accepts an array of String object as argument.
19. Can a main() method be overloaded?
Yes. You can have any number of main() methods with different method signature
and implementation in the class.
20. Can a main() method be declared final?
Yes. Any inheriting class will not be able to have it’s own default main() method.