Wait for all threads in a array to die

Question

I everyone. I'm from Portugal and I have some experience in JAVA programming (approximately five years) but this is the first the first time that i'm trying to use threads. I'm trying to learn writing some simpler code that does almost exactly at the basic level the same stuff that a complex application that I need to write for my work.
What I'm trying to do is execute a counter that counts all operations in threads belonging to the same array (an array of n threads).
A static variable in the Thread class (implementing Runnable) counts all operations performed by all threads and sums them all and shoud display the total of operations after all threads terminate, but this exactly what I don't know how to do:
This is my example code:
public class TT1 implements Runnable {
     int id;
     double last_number;
     static int threads_counter = 0;
     static int total_threads = 4;
     static long total_numbers;
     int total_randoms = 1000;
     public void run() {
          for (int i=0;i<total_randoms;i++)
               total_numbers++;
               // does some stuff, in this case, generate a random number!
               last_number = Math.random();
          System.out.printf("Thread %d:%f(%d)\n",id,last_number,total_numbers);
     public TT1() {
          id = threads_counter++;
          new Thread(this).start();
     public static void main(String[] args) {
          // TODO Auto-generated method stub
          Thread [] threads = new Thread[total_threads];
          for (int i=0;i<threads.length;i++)
               threads[i] = new Thread(new TT1());
          /* commented code using join(), is not working or I don't know
          how to use it! */
          for (int i=0;i<threads.length;i++)
               try {
                    threads.join();
               } catch (InterruptedException e) {
                    e.printStackTrace();
          try {
               threads[total_threads-1].join();
          } catch (InterruptedException e) {
               e.printStackTrace();
          // this line should be executed ONLY after ALL threads have died!
          System.out.println("******GENERATED NUMBERS TOTAL:" + total_numbers);
Somebody can give me a hint how to solve this ?

Answer 1

Thanks for your replies.
Actually, i've corrected the code, now i'm starting the threads outside the constructor. Originally I thought this could be a simpler way to create the threads: launching them at same time I'm creating them! Is this wrong ? :) Well, watching the results.
I changed my code:
public class TT1 implements Runnable {
     int id;
     double last_number;
     static int threads_counter = 0;
     static int total_threads = 4;
     static long total_numbers;
     int total_randoms = 1000;
     public void run() {
          for (int i=0;i<total_randoms;i++)
               total_numbers++;
               // does some stuff, in this case, generate a random number!
               last_number = Math.random();
          System.out.printf("Thread %d:%f(%d)\n",id,last_number,total_numbers);
     public TT1() {
          id = threads_counter++;
     public static void main(String[] args) {
          // TODO Auto-generated method stub
          Thread [] threads = new Thread[total_threads];
          /* create individual threads */
          for (int i=0;i<threads.length;i++)
               threads[i] = new Thread(new TT1());
          /* launch the threads (NEW CODE) */
          for (int i=0;i<threads.length;i++)
               threads.start();
          /* commented code using join(), is not working or I don't know
          how to use it! */
          for (int i=0;i<threads.length;i++)
               try {
                    threads[i].join();
               } catch (InterruptedException e) {
                    e.printStackTrace();
          // this line should be executed ONLY after ALL threads have died!
          System.out.println("******GENERATED NUMBERS TOTAL:" + total_numbers);
And I obtain the output:
$ java TT1
Thread 0:0,191546(1000)
Thread 1:0,937476(2000)
Thread 2:0,825079(3000)
Thread 3:0,451367(4000)
******GENERATED NUMBERS TOTAL:4000Exactly as I want it!
All is good when it works good ;)
Best regards