Example of Thread.join

ThreadDemoForWait_FactThread.java

package ThreadDemoForWait;

public class FactThread implements  Runnable{
    int i, fact=1;
    @Override
    public void run() {
        for (int i = 1; i <=5 ; i++) {
            fact*=i;
            System.out.println("\nFactorial of " + i + " = " + fact);
        }
    }
}

ThreadDemoForWait_SumThread.java

package ThreadDemoForWait;
/*
* SumThread class to process sum of first 5 natural numbers.
* */
public class SumThread implements Runnable{
    int i, sum=0;

    @Override
    public void run() {
        for (int i = 1; i <=5 ; i++) {
            sum+=i;
            System.out.println("\nSum of number from 1 to " + i+  "  =" + sum);
        }
    }
}

ThreadDemoForWait_ThreadJoinDemo.java

package ThreadDemoForWait;
/*
* In some problems, it may be required to wait for a particular thread to complete its task before another thread to proceed with.
* In such occasions, the join method of Thread class can be used.
* When join method is call on a thread object the control waits for the thread to complete its task and becomes a dead thread.
* The join method allows one thread to wait for the completion of another. If t is a Thread object whose thread is currently executing, t.join();
* Reference:
*  https://docs.oracle.com/javase/tutorial/essential/concurrency/join.html
* Programming in JAVA2 Dr. K. Somasundaram

causes the current thread to pause execution until t's thread terminates.
* */
public class ThreadJoinDemo {
    public static void main(String[] args) {
        SumThread st = new SumThread();
        FactThread ft = new FactThread();
        Thread sumt = new Thread(st,"Sum Thread");
        Thread factt = new Thread(ft,"Fact Thread");
        sumt.setPriority(Thread.NORM_PRIORITY-3);
        factt.setPriority(Thread.NORM_PRIORITY+3);
        sumt.start();
        try {
            sumt.join();
        } catch (InterruptedException e) {
            System.out.println(e.toString());;
        }
        factt.start();
    }
}

Sample Output:
Sum of number from 1 to 1 =1

Sum of number from 1 to 2 =3

Sum of number from 1 to 3 =6

Sum of number from 1 to 4 =10

Sum of number from 1 to 5 =15

Factorial of 1 = 1

Factorial of 2 = 2

Factorial of 3 = 6

Factorial of 4 = 24

Factorial of 5 = 120