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Old February 20th, 2007, 09:30 AM
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Default a Thread argument


I am kind of new around her but i studied java since 6 months;

so this is the problem , i have a method that takes as an argument a Thread object; an by all specs it should take it by refference not by value; but my method seems to do backwards; this is the method :

public void startThread (Thread e) {

        if(e == null) {

            e = new Thread(this);


and for who wants the whole file here it is :

import javax.swing.*;

class updateThread
implements Runnable {

    Thread t,w;
    int s;
    boolean b;

    public updateThread(){};

    public static void main (String args[]) {

        updateThread obj = new updateThread();


    public void startThread (Thread e) {

        if(e == null) {

            e = new Thread(this);

    public void run() {

         try {
             while(true ) { s++;
                System.out.print("\n\n\n\n\t for s= "+s+"\n\t thread t "+ t+"\n\n\t thread w "+w);
                if(s == 3) {stopThread();s=0;};

         catch(Exception e) { System.out.print("\n\n\n\t Exception "+e+"\n\n\n\n");};

    public void stopThread ( ) {

        if(true) {

            b = !b;

            if(!b) { w = t;
            t= null;}else{t = w; w = null;};
                    System.out.print("\n\n\n\n\t\t ****** thread change ********\n\n\n");



Ok ,so if u just watch closely at my method u see (after compilation)that e(pointing to obj.t) takes a value (from code : e = new Thread(this);) so ok but it does not affect t aswell; why? it should as it is passed by refference .

                     Thank u in advance.

  #2 (permalink)  
Old February 21st, 2007, 06:12 AM
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e = new Thread(this);

means e is now a reference to a new Thread object. what was e referencing before doesn't matter(null or another Thread object).

I think you missed that references are passed by value, i.e.
t = new Thread();
e = t;
... changes to t and e are equal
e = new Thread();
... t and e now reference different objects

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