How do I change this program to create 50 threads? My code creates only 47 threads.

Question

1.00/5 (1 vote)

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Quote:
The question is-
Write a program called ReverseHello.java that creates a thread (let's call it Thread 1). Thread 1 creates another thread (Thread 2); Thread 2 creates Thread 3; and so on, up to Thread 50. Each thread should print "Hello from Thread <num>!", but you should structure your program such that the threads print their greetings in reverse order.

Java

class reversehello extends Thread{
	public void run()
	{
		for(int j=49;j>=0;j--)
			System.out.println("Hello from Thread <"+(j+1)+">");
		try{
			Thread.sleep(1000);
		}
		catch(Exception e)
		{System.out.println(e);}
	}
	public static void main(){
		reversehello t[]=new reversehello [50];
		for(int i=0;i<50;i++)
			t[i]=new reversehello();
		for(int i=49;i>=0;i--)
			t[i].start();
	}
}

What I have tried:

I have tried creating array of size 53 and running from 52 to 0,but the output was same.It creates only 47 threads.

Posted 16-Aug-16 12:45pm

Anurita Srivastava

Updated 23-Mar-17 4:47am

Patrice T

v2

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Comments

Philippe Mori 16-Aug-16 19:02pm

Why would you have a loop in both run function and in main function?

Anurita Srivastava 17-Aug-16 14:54pm

The loop in main is to start() the threads and in run is to print the output,to actually print the number of thread.

Mohibur Rashid 16-Aug-16 19:39pm

How do you know that it creates only 47?

Anurita Srivastava 17-Aug-16 14:53pm

because the output prints only till Hello from Thread 47.

Mohibur Rashid 17-Aug-16 19:59pm

Your application runs all 50 threads + 1(main thread). But your logic is incorrect. Follow what Richard MacCutchan said

Patrice T 16-Aug-16 23:07pm

Program do not match the statements, it is plain wrong.
it output something like 2500 hello messages.

Richard MacCutchan 17-Aug-16 3:51am

You have started all threads from your main thread, which is not what the instructions are telling you. Main thread is supposed to start Thread 1, which is supposed to start Thread 2 etc.

4 solutions

Solution 1

Since your main problem is having 47 threads instead of 50 and that you did not noticed 2500 'Hello' messages instead of 50, I suspect the problem is your method of counting.

Quote:
The question is-
Write a program called ReverseHello.java that creates a thread (let's call it Thread 1). Thread 1 creates another thread (Thread 2); Thread 2 creates Thread 3; and so on, up to Thread 50. Each thread should print "Hello from Thread !", but you should structure your program such that the threads print their greetings in reverse order.

Your code is not doing this at all, It is not a little different, it is completely different. A complete rewrite is in order.

Posted 16-Aug-16 19:33pm

Patrice T

Solution 3

This is my very quick solution. There are improvements to be made.

C#

class reverseGreeting extends Thread
{
  private int counter;
 public reverseGreeting(int counter)
 {
   super("Thread" + counter);
   this.counter = counter;
 }
  
 public void run()
 {
    counter++ ;
   if(counter <= 51)
   {
   reverseGreeting thr = new reverseGreeting(counter);
  thr.start();
  try {
    thr.join();
     System.out.println("Hello from "+ getName()); 
  }
  catch (Exception e)
  {
   //do smth
  }
   }
 } 

 public static void main (String args[])
 {
   reverseGreeting th1 = new reverseGreeting(1);
   th1.start();
 }
 
}

Posted 31-Oct-16 17:37pm

Member 12759301

Solution 4

class App extends Thread{
	int counter;
	public App(int counter){
		this.counter=counter;
	}
	public void run()
	{
		if(counter<50)
		{
			createThread(counter+1);	
		}
		System.out.println("hello" + counter);	
	}
	public void createThread(int counter) {
		App t=new App(counter);
		t.start();		
		try {
			t.join();
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}				
	}
	public static void main(String[] arg){		
		App t = new App(1);
		t.start();		
	}
}

Posted 23-Mar-17 4:47am

Member 13079813

Updated 23-Mar-17 4:51am

v2

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Richard MacCutchan · Accepted Answer · 2016-08-16T23:11:00

Solution 2

Some logic to think about:
1. The thread object needs to be given a number to tell it what sequence number it is.
2. If the sequence number is less than 51 then:
2.1. It should create a new child thread with the sequence number + 1.
2.2. It should then start the child thread and wait for it to finish.
3. It should print the "Hello" message with its sequence number.
4. It should then return.

The main method of the class should create the first thread with sequence number 1, and then start it - no need to wait for it to finish.

Posted 16-Aug-16 23:11pm

Richard MacCutchan

Updated 16-Aug-16 23:19pm

v4

Comments

Anurita Srivastava 17-Aug-16 15:01pm

How do I give a number to my thread?Can you please explain in details?

Richard MacCutchan 18-Aug-16 3:19am

Add an integer field to your reversehello class, and a constructor that takes an integer value. The constructor can then save it, and the code in your run method can check it.

Anurita Srivastava 28-Aug-16 10:49am

oh,thanks :)