concurrency Getting started with concurrency Example of concurrent execution in Java

Example

import java.util.stream.IntStream;

public class Concurrent {
    public static void printAndWait(String s) {
        System.out.println(s);
        try {
            Thread.sleep(1000);
        } catch (Exception e) {}
    }
    
    public static void main(String[] args) {
        Thread myThread = new Thread() {
            public void run() {
                IntStream.range(1,32)
                .forEach(x -> printAndWait(""+x));
            }
         };
         myThread.start();
         IntStream.range('a', 'z').forEach(x -> printAndWait(""+(char)x));
     }
}

This will produce an output of something similar to

a
1
b
2
c
3

and so on, though results may vary. This is because the code in myThread is executed simultaneously, in a different thread, as the main flow. That is, the range 1-32 is handled by one thread, and the range a-z is handled by another.

Since there is no synchronization between the threads, there is no guarantee which one will execute first or indeed even that they will produce a result that is perfectly intertwined.