Java Thread Join Examples

• Imagine the following scenario. You are preparing for tomorrow's final examination and feel a little hungry. So, you give your younger brother ten bucks and ask him to buy a pizza for you. In this case, you are the main thread and your brother is a child thread. Once your order is given, both you and your brother are doing their job concurrently (i.e., studying and buying a pizza). Now, we have two cases to consider. First, your brother brings your pizza back and terminates while you are studying. In this case, you can stop studying and enjoy the pizza. Second, you finish your study early and sleep (i.e., your assigned job for today - study for tomorrow's final exam - is done) before the pizza is available. Of course, you cannot sleep; otherwise, you won't have a chance to eat the pizza. What you are going to do is to wait until your brother brings the pizza back.
• A thread can execute a thread join to wait until the other thread terminates
• A parent thread may join with many child threads created by the parent. Or, a parent only join with some of its child threads, and ignore other child threads. In this case, those child threads that are ignored by the parent will be terminated when the parent terminates.

Thread Join Sample Code

package com.myjava.threads;

import java.util.ArrayList;
import java.util.List;

public class MyThreadJoin {

    public static List<String> names = new ArrayList<String>(); 
    
    public static void main(String a[]){
        List<SampleThread> list = new ArrayList<SampleThread>();
        for(int i=0;i<5;i++){
            SampleThread s = new SampleThread();
            list.add(s);
            s.start();
        }
        for(SampleThread st:list){
            try{
                st.join();
            } catch (Exception ex){}
        }
        System.out.println(names);
    }
}

class SampleThread extends Thread{
    
    public void run(){
        for(int i=0; i<10; i++){
            try{
                Thread.sleep(10);
            } catch(Exception ex){}
        }
        MyThreadJoin.names.add(getName());
    }
}

Example Output

[Thread-0, Thread-2, Thread-1, Thread-4, Thread-3]

Other Thread Examples

• By Implementing Runnable Interface Example
• By Extending Thread Class Example
• Daemon Thread Example
• Thread Sleep Example
• Thread Yield Example