2nd thread for loop not executing in Java8

user_3663271 0
Viewed 47

I'm new to Java threads. I'm solving a question where I've been given a Solution.java class which executes 3 java threads from 3 different Thread extended classes that I've wrote. Following is the way that the predefined class is using to start threads:

public class Solution {
        public static final int[] threadArray = new int[300];
        public static volatile String i = 0+"";
    public boolean test() throws InterruptedException
    {
        Task1 task1 = new Task1();
        Task2 task2 = new Task2();
        Task3 task3 = new Task3();
        Thread task2Thread = new Thread(task2);
        Thread task3Thread = new Thread(task3);
        task1.start();
        task2Thread.start();
        task1.join();
        task2Thread.join();
        task3Thread.start();
        int first = Task1.a+Task2.a;
        int containsSecondThread = Task1.a;
        String oneAndTwo = "";
        String sizeOfTask1 = "";
        for(int i=0;i<first;i++)
        {
            oneAndTwo += threadArray[i]+" ";
        }
        for(int i=0;i<containsSecondThread;i++)
        {
            sizeOfTask1 += threadArray[i]+" ";
        }
        int begOfTask3 = Task3.beg;
        String checkingString = "";
        for(int i=begOfTask3;i<threadArray.length;i++)
        {
            checkingString += i + " ";
        }
        String task3String = "";
        for(int j = begOfTask3;j<threadArray.length;j++)
        {
            task3String += threadArray[j]+" ";
        }
        if((!oneAndTwo.contains(begOfTask3+"") && sizeOfTask1.contains(Task2.beg+"")) && task3String.equals(checkingString))
        {
            return true;
        }
        return false;
    }
    public static void main(String[] args) throws InterruptedException 
    {
        Scanner sc= new Scanner(System.in);
            Solution solution = new Solution();
            int one = sc.nextInt();
            Task1.a = one;
            Task1.beg = 0;
            int two = sc.nextInt();
            Task2.a = two;
            Task2.beg = one;
            int three = sc.nextInt();
            Task3.a = three;
            Task3.beg = one+two;
            System.out.print(solution.test());
    }
}

Aim of the question is to run task1 and task2 simultaneously. And then run task3 after complete execution of both task1 and task2. Following is my thread classes implementation:

class Task1 extends Thread{    
    public static int a;
    public static int beg;
    @Override
    public void run(){
        for(int k=beg;k<a;k++){
            int idx = Integer.parseInt(Solution.i);
            Solution.threadArray[idx] = k;
            idx++;
            Solution.i = Integer.toString(idx);
        }
    }
    
}

class Task2 implements Runnable{
    public static int a;
    public static int beg;
    @Override
    public void run(){
        for(int k=beg;k<a;k++){
            int idx = Integer.parseInt(Solution.i);
            Solution.threadArray[idx] = k;
            idx++;
            Solution.i = Integer.toString(idx);
        }        
    }
    
}

class Task3 implements Runnable{
    public static int a;
    public static int beg;
    @Override
    public void run(){
        for(int k=beg;k<300;k++){
            int idx = Integer.parseInt(Solution.i);
            Solution.threadArray[idx] = k;
            idx++;
            Solution.i = Integer.toString(idx);
        }        
    }
    
}

The issue is that only task1 is executing. No other thread is running and I don't understand why. I'll be really glad if someone could help me out with this one.

Edit: I've added the complete Solution.java class. Also I've changed a little bit of code in classes implemented by me. I'm sorry for not testing it earlier, but all the threads are running. Only issue is that for loop in second thread is not running. I used System.out.println inside and outside the for loop and that's how I got to know it.

multithreading java
1 Answers

What evidence do you have that only one thread is executing?

What I'd expect from analysing your code is that all three threads should execute, but task1 and task2 should finish almost instantly (probably in less than 1ms), while task3 should take longer but still finish quickly (probably in less than 1 sec).

The reason for the different run-times is that task1 and task2 both have a loop relying on static int fields which are never given a value, so those fields have the default value of 0. Where you have lines like for(int k=beg;k<a;k++), but beg and a are both 0, those loops exit immediately without iterating.
With task3, you compare the loop counter to the constant 300 so it should run 300 iterations.

It might help if you include the rest of the Solution.java class you were given, since what you have included clearly isn't complete.

user_186030
Related