CODEWITHSUNDEEP
javamultithreading
Xuzheng Wang
Xuzheng Wang

Reputation: 531

duplicate output in multithreading java

I am new to multithread programming. The code does not do what I want :

public class Test {
    static int i;
    public static void main(String[] args) {
        ExecutorService executor = Executors.newFixedThreadPool(10);
        for(i = 0; i<10 ;i++) {
             executor.execute(new Runnable() {
                 public void run () {
                     System.out.println(i);
                 }
            });
        }
    }
}

output : 2 4 3 4 2 6 6 8 9 10

I expect it to output something like 0,1,2,3,4,5,6,7,8,9 with or without order. My question is what i can do to get my expected output, and how to make them in order.

Thanks in advance

Upvotes: 1

Views: 232

Answers (2)

ka4eli
ka4eli

Reputation: 5424

Don't pass static i to run:

public class Test {
    public static void main(String[] args) {
    ExecutorService executor = Executors.newFixedThreadPool(10);
    for(int i = 0; i < 10 ;i++){
         int x = i;
         executor.execute(new Runnable(){
         public void run (){
             System.out.println(x);
         }
     });
    }    
    }
}

Upvotes: 2

M A
M A

Reputation: 72844

You can have a class that implements Runnable and copy the static field into an instance field with a constructor:

executor.execute(new MyRunnable(i));


class MyRunnable implements Runnable {
     int i;

     public MyRunnable(int i) {
         this.i = i;
     }

     // run method
 }

This guarantees that each thread has its own unique integer with exactly the same order of i in the for loop.

Upvotes: 0

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