JavaRocks.java

package com.github.rxrav.java21bootcamp;

public class JavaRocks {
    private final int times;
    private boolean shouldPrintJava = true;
    public JavaRocks(int times) {
        this.times = times;
    }

    public synchronized void printJava(Runnable action) throws InterruptedException {
        for (int i = 0; i < this.times; i ++) {
            if (shouldPrintJava) {
                action.run();
                shouldPrintJava = false;
                notify();
            }
            wait();
        }
        // when print-java is done, notify print-rock to complete
        // so, it doesn't wait any longer...
        notify();
    }

    public synchronized void printRocks(Runnable action) throws InterruptedException {
        for (int i = 0; i < this.times; i ++) {
            if (!shouldPrintJava) {
                action.run();
                shouldPrintJava = true;
                notify();
            }
            wait();
        }
    }

    public static void main(String[] args) throws InterruptedException {
        var javaRocks = new JavaRocks(10);

        var javaPrinter = Thread.ofPlatform()
                .name("java-printer")
                .unstarted(() -> {
                    try {
                        javaRocks.printJava(() -> System.out.print("Java "));
                    } catch (InterruptedException e) {
                        throw new RuntimeException(e);
                    }
                });
        var rocksPrinter = Thread.ofPlatform()
                .name("rock-printer")
                .unstarted(() -> {
                    try {
                        javaRocks.printRocks(() -> System.out.print("Rocks!\n"));
                    } catch (InterruptedException e) {
                        throw new RuntimeException(e);
                    }
                });

        javaPrinter.start();
        rocksPrinter.start();

        javaPrinter.join();
        rocksPrinter.join();
    }
}

Solution to this problem https://gist.github.com/rokon12/cc1d1b3359cec8e4fdbcac6f2f1d5342