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Thread question

Submitted by i-robot on Thu, 10/16/2008 - 11:48.
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example code from "Java The Programming Language (3rd)"

public class Friendly {

    private Friendly partner;
    private String name;

    public Friendly(String name) {
        this.name = name;
    }

    public synchronized void hug() {
        System.err.println(Thread.currentThread().getName()
        + " in " + name + ".hug() trying to invoke "
        + partner.name + ".hugback()");
        partner.hugback();
    }

    private synchronized void hugback() {
        System.out.println(Thread.currentThread().getName()
        + " in " + name + ".hugback()");
    }

    public void becomdeFriend(Friendly partner) {
        this.partner = partner;
    }

    public static void main(String[] args) {

        final Friendly jareth = new Friendly("jareth");
        final Friendly cory = new Friendly("cory");

        jareth.becomdeFriend(cory);
        cory.becomdeFriend(jareth);

        new Thread(new Runnable() {
            public void run() {
                jareth.hug();
            }
        }, "Thread1").start();

        new Thread(new Runnable() {
            public void run() {
                cory.hug();
            }
        }, "Thread2").start();
    }
}

Obviously, it may come to a deadlock.
But when it works ok, sometimes it gives result like:

run:  
Thread1 in cory.hugback()  
Thread1 in jareth.hug() trying to invoke cory.hugback()  
Thread2 in cory.hug() trying to invoke jareth.hugback()  
Thread2 in jareth.hugback()  
BUILD SUCCESSFUL (total time: 0 seconds) 

or
run:  
Thread1 in cory.hugback()  
Thread2 in jareth.hugback()  
Thread1 in jareth.hug() trying to invoke cory.hugback()  
Thread2 in cory.hug() trying to invoke jareth.hugback()  
BUILD SUCCESSFUL (total time: 0 seconds)

I can't figure out the order of the messages. How can it be ?
Can you give me explanation?
Thanks in advance.