Interview Questions - Core Java

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.

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 MAX_LENGTH = 50; is an example for constant.

No not required. main() method should be defined only if the source class is a java application.

Main() method doesn't return anything hence declared void.