Java thread Programming - Find and Print Even-Odd Numbers with Threads

Java Thread: Exercise-2 with Solution

Write a Java program that creates two threads to find and print even and odd numbers from 1 to 20.

Sample Solution:

Java Code:

public class Find_Even_Odd_Number {
  private static final int MAX_NUMBER = 20;
  private static Object lock = new Object();
  private static boolean isEvenTurn = true;

  public static void main(String[] args) {
    Thread evenThread = new Thread(() -> {
      for (int i = 2; i <= MAX_NUMBER; i += 2) {
        synchronized(lock) {
          while (!isEvenTurn) {
            try {
              lock.wait();
            } catch (InterruptedException e) {
              e.printStackTrace();
            }
          }
          System.out.println("Even Number from evenThread: " + i);
          isEvenTurn = false;
          lock.notify();
        }
      }
    });

    Thread oddThread = new Thread(() -> {
      for (int i = 1; i <= MAX_NUMBER; i += 2) {
        synchronized(lock) {
          while (isEvenTurn) {
            try {
              lock.wait();
            } catch (InterruptedException e) {
              e.printStackTrace();
            }
          }
          System.out.println("Odd Number from oddThread: " + i);
          isEvenTurn = true;
          lock.notify();
        }
      }
    });

    evenThread.start();
    oddThread.start();
  }
}

Sample Output:

 Even Number from evenThread: 2
Odd Number from oddThread: 1
Even Number from evenThread: 4
Odd Number from oddThread: 3
Even Number from evenThread: 6
Odd Number from oddThread: 5
Even Number from evenThread: 8
Odd Number from oddThread: 7
Even Number from evenThread: 10
Odd Number from oddThread: 9
Even Number from evenThread: 12
Odd Number from oddThread: 11
Even Number from evenThread: 14
Odd Number from oddThread: 13
Even Number from evenThread: 16
Odd Number from oddThread: 15
Even Number from evenThread: 18
Odd Number from oddThread: 17
Even Number from evenThread: 20
Odd Number from oddThread: 19

Explanation:

The evenThread prints even numbers. It starts with 2 and increments by 2 in each iteration until it reaches MAX_NUMBER (which is 20 in this case). It uses a synchronized block with a while loop to check if it's its turn to print. If not, it waits by calling lock.wait(). When it's its turn, it prints the even number and notifies the oddThread by calling lock.notify().

The oddThread prints odd numbers. It starts with 1 and increments by 2 in each iteration until it reaches MAX_NUMBER. Similar to the evenThread, it uses a synchronized block with a while loop to check if it's its turn to print. If not, it waits by calling lock.wait(). When it's its turn, it prints the odd number and notifies the evenThread by calling lock.notify().

Flowchart:

Java Code Editor:

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