Default initializations of static and instance variables. : Member Variable « Java Source And Data Type « SCJP

Integer primitives are initialized to 0.

Floating-point primitives are initialized to 0.0.

Boolean primitives are initialized to false.

Reference variables are initialized to null.

public class MainClass{
    static int i;
    public static void main(String[] argv){

1.20.Member Variable
1.20.1.Field Variables are variables that are declared as members of classes.
1.20.2.Field variables are declared using the following syntax: modifiers Type declarator;
1.20.3.Java supports two different kinds of variables: field variables and local variables.
1.20.4.Field variables of object types and the elements of arrays of object types are automatically initialized to the null value.
1.20.5.Initialization Values for Member Variables(the same as array element initialization values)
1.20.6.Default initializations of static and instance variables.
1.20.7.A member value may be initialized in its own declaration line:
1.20.8.nonstatic instance variables are initialized before the class constructor is executed
1.20.9.Non-initialized string instance variable
1.20.10.Array Instance Variables