Boolean literals are the source code representation for boolean values. : boolean « Java Source And Data Type « SCJP

1. SCJP
2. Java Source And Data Type
3. boolean

A boolean value can only be defined as true or false. 

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

        boolean t = true;  // Legal
        boolean  f = 0;    // Compiler error!

        System.out.println();

    }
}

Type mismatch: cannot convert from int to boolean