Problem:
How to create a task running as a Java Thread? Thread and Runnable are the most basic concurrent types to use. In this post we show how to use Thread to execute concurrent tasks.
Solution:
In the previous post you could learn how to correctly use Runnable interface. In this post we show how to create a task that directly extends from java.lang.Thread class and run two instances to do their jobs concurrently:
package com.farenda.java.lang;
public class ThreadExample {
private static class Counter extends Thread {
// it's only to generate unique ids for each task:
private static int threads = 0;
private int id = ++threads;
private final int number;
public Counter(int number) {
this.number = number;
}
@Override
public void run() {
for (int i = 0; i < number; ++i) {
System.out.printf("counter %d, value: %d%n", id, i);
}
}
}
public static void main(String[] args) {
Counter counter1 = new Counter(5);
Counter counter2 = new Counter(5);
System.out.println("Starting counters:");
counter1.start();
counter2.start();
System.out.println("main thread ends here");
}
}
Whole task implementation is performed run() method. Note that threads are not started when instantiated, but only after call to start() method.
And here’s the output of the above program:
Starting counters: counter 1, value: 0 counter 1, value: 1 counter 1, value: 2 counter 2, value: 0 counter 2, value: 1 counter 2, value: 2 counter 2, value: 3 counter 2, value: 4 main thread ends here counter 1, value: 3 counter 1, value: 4
As you can see the execution of threads is non-deterministic and can occur in any order – here part of the first thread job has been executed after thread two.
Also note that the program finishes only when all the threads have finished the work.
