Sequential Execution of Two Threads Printing Numbers (1,2,3…) and Letters(A,B,C,..) in Java. So that it prints (1,A,2,B…)?

To ensure that two threads print in sequence — one printing numbers (1,2,3…) and the other printing letters (A,B,C…) — you can use synchronization mechanisms such as Locks and Condition Variables, Synchronized Blocks & Wait/Notify, or Atomic Variables & Busy-Waiting. Below is a solution using Lock and Condition from java.util.concurrent, which ensures proper sequencing.

Solution1 :

package com.example.validation_demo.controller;

public class PrintTest {
    private final Object lock = new Object();
    private boolean numberTurn = true; // Indicates whether it's the number thread's turn

    public static void main(String[] args) {
        PrintTest printer = new PrintTest();
        Thread numberThread = new Thread(() -> printer.printNumbers());
        Thread letterThread = new Thread(() -> printer.printLetters());
        numberThread.start();
        letterThread.start();
    }
    public void printNumbers() {
        for (int i = 1; i <= 26; i++) { // Adjust the range as needed
            synchronized (lock) {
                while (!numberTurn) {
                    try {
                        lock.wait(); // Wait until it's this thread's turn
                    } catch (InterruptedException e) {…