What are the rules for initializing variables?

In Java, every variable in a program must have a value before its value is used.

• Member variables (both static and instance) are initialized implicitly by default:
  • Most primitives except boolean are default initialized to zero (e.g., the value for integer type is 0, 0.0f is for float type, and 0.0d is for double type)
  • char variables are default initialized to '\u0000'
  • boolean variables are default initialized to false.
  • The reference type variables are default initialized to null.
• Final variables must be initialized explicitly in declaration or constructors (instance final variable.)
• Local variables are not assigned a default value. A local variable must be explicitly given a value before it is used, by either initialization or assignment, in a way that can be verified by the compiler using the rules for definite assignment.