Example for http://blog.m-siemens.de/exploring-computers-threads-are-easy/

gistfile1.java

import java.util.ArrayList;

class SyncedExample extends Thread {
    private static int counter = 0;
    private static final Object lock = new Object();

    public static void main(String[] args) throws Exception {
        ArrayList<SyncedExample> threads = new ArrayList<SyncedExample>();

        // Create 10 threads
        for (int i = 0; i < 10; i++) {
            SyncedExample thread = new SyncedExample();
            thread.start();

            threads.add(thread);
        }

        // Wait for all threads to finish
        for (SyncedExample thread : threads) {
            thread.join();
        }

        System.out.println(counter);
    }

    // The function that will be called in each thread
    public void run() {
        for (int i = 0; i < 100_000; i++) {
            synchronized(lock){
                counter += 1;
            }
        }
    }
}