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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.

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