Question

My expected output is

Count : 1
Count : 2
Count : 3
Count : 4
Count : 5

I have tried synchronized and Lock but neither of them works. I reach to

Ending Main

sooner than I finish the loop completely. Current output is:

Starting Main
Count : 1
Count : 2
Count : 3
Count : 4
Ending Main
Count : 5

Any Idea why Count : 5 is after Ending Main? Here is my code:

public class Demo {
    public static void main( String [] args ) {
        System.out.println( "Starting Main" ) ;
        for ( int i = 1 ; i <= 5 ; i++ ) {
            Thread numberThread = new Thread(new NumberTask(i)) ;
            numberThread.start() ;
        }
        System.out.println( "Ending Main" ) ; 
    }
}

class NumberTask implements Runnable {
    private Lock bankLock = new ReentrantLock();
    int count ;
    public NumberTask( int count ) {
        this.count = count ;
    }

    synchronized public void run() {
        bankLock.lock();
        try {
            System.out.println( "Count : " + count ) ;
        } finally {
            bankLock.unlock();
        }
    }
}

Answer 1

You can use join() to wait for other thread to finish. Your code need to be updated as follows:

public static void main( String [] args ) {

    System.out.println( "Starting Main" ) ;
        Thread numberThread;
        for ( int i = 1 ; i <= 5 ; i++ ) {
            numberThread = new Thread(new NumberTask(i)) ;
            numberThread.start() ;
        }
        numberThread.join();
        System.out.println( "Ending Main" ) ; 
    }