Question

Could anyone explain how Java executes this code? I mean the order of executing each statement.

public class Foo
{
    boolean flag = sFlag;
    static Foo foo = new Foo();
    static boolean sFlag = true;

    public static void main(String[] args)
    {
        System.out.println(foo.flag);
    }
}

OUTPUT:

false

Answer 1

• Class initialization starts. Initially, foo is null and sFlag is false
• The first static variable initializer (foo) runs:
  • A new instance of Foo is created
  • The instance variable initializer for flag executes – currently sFlag is false, so the value of flag is false
• The second static variable initializer (sFlag) executes, setting the value to true
• Class initialization completes
• main runs, printing out foo.flag, which is false

Note that if sFlag were declared to be final it would be treated as a compile-time constant, at which point all references to it would basically be inlined to true, so foo.flag would be true too.