Question on Thread

[Raghavendra Desoju]

Hi,

Here is the program I ran:

import java.util.*;
import java.util.stream.*;
public class ListTest {
	static List<Integer> list = new ArrayList<>();
	public static void main (String[] args) {
		IntStream.range(1,101).forEach(i->list.add(i));
		System.out.println(list);
		
		new Thread(new Runnable () {
			public void run() {
				while(list.size() > 0) {
				System.out.println("Removing1: "+list.remove(0));
				list.remove(0);
				}
			}
		}).start();
		new Thread(new Runnable () {
			public void run() {
				while(list.size()>0){
				System.out.println("Removing2: "+list.remove(0));
				
				}
			}
		}).start();
		
	}

		
}

Here is the output it printed:


Removing1: 1
Removing1: 3
Removing1: 5
Removing1: 7
Removing1: 9
Removing2: 10
Removing2: 13
Removing1: 12
Removing1: 16
Removing2: 14
Removing1: 18
Removing2: 19
Removing1: 21
Removing2: 22
Removing1: 24
Removing2: 25
Removing1: 27
Removing2: 28
Removing2: 31
Removing1: 30
Removing2: 32
Removing1: 34
Removing2: 35
Removing1: 37
Removing2: 38
Removing1: 40
Removing2: 41
Removing1: 43
Removing2: 44
Removing1: 46
Removing2: 47
Removing2: 50
Removing1: 49
Removing2: 51
Removing1: 53
Removing2: 54
Removing1: 56
Removing2: 57
Removing1: 59
Removing2: 60
Removing1: 62
Removing2: 63
Removing1: 65
Removing2: 66
Removing1: 68
Removing2: 69
Removing1: 71
Removing2: 72
Removing1: 74
Removing2: 75
Removing1: 77
Removing2: 78
Removing1: 80
Removing2: 81
Removing1: 83
Removing2: 84
Removing1: 86
Removing2: 87
Removing1: 89
Removing2: 90
Removing1: 92
Removing2: 93
Removing1: 95
Removing2: 96
Removing1: 98
Removing2: 99

I see it is missing up lot of numbers in between. Could someone please clarify what is happening?

Thanks, Raghu

[Ron McLeod]

The first thread is removing two elements, but only printing the value of one of them.

[Raghavendra Desoju]

Yikes, yet another programming mistake

[chandana nalin]

You can use Java synchronized method

If you declare any method as synchronized, it is known as synchronized method.

Synchronized method is used to lock an object for any shared resource.

When a thread invokes a synchronized method, it automatically acquires the lock for that object and releases it when the thread completes its task.

//example of java synchronized method
class Table{
 synchronized void printTable(int n){//synchronized method
   for(int i=1;i<=5;i++){
     System.out.println(n*i);
     try{
      Thread.sleep(400);
     }catch(Exception e){System.out.println(e);}
   }
 }
}

class MyThread1 extends Thread{
  Table t;
  MyThread1(Table t){
    this.t=t;
  }
  public void run(){
    t.printTable(5);
  }
}
class MyThread2 extends Thread {
  Table t;
  MyThread2(Table t) {
    this.t=t;
  }
  public void run(){
    t.printTable(100);
  }
}

public class TestSynchronization2{
  public static void main(String args[]){
    Table obj = new Table();//only one object
    MyThread1 t1=new MyThread1(obj);
    MyThread2 t2=new MyThread2(obj);
    t1.start();
    t2.start();
  }
}

Output: 5
10
15
20
25
100
200
300
400
500