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

Last update on May 09 2025 12:50:44 (UTC/GMT +8 hours)

2. Use two threads to print even and odd numbers

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:

For more Practice: Solve these Related Problems:

• Write a Java program to create two threads where one prints even numbers and the other prints odd numbers from 1 to 50 concurrently with proper synchronization.
• Write a Java program to implement two threads that alternate printing even and odd numbers using wait() and notify() for coordination.
• Write a Java program to create two threads that concurrently print even and odd numbers from 1 to 100 and then join the threads to ensure complete execution.
• Write a Java program to implement two threads that print even and odd numbers and use a shared lock object to avoid mixed output.

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