Question

Please bear with me on this as I’m still getting the hang on Java.

The example bellow reads from a Class named Parent that creates an instance of itself on the main method. It then makes that instance do all sorts of calculations.

Next it fires up a thread named Child passing the Parent instance as a reference to Child.

The Child just sits there monitoring things and, sometimes, fires up public methods on Parent.

It works. The question is, is this poor style? Is there a more Java thinking way of doing this sort of work?

public class Parent {

    // main function that fires up the program
    public static void main() {

        // creates an instance of himself
        // and fires go that does all sorts of fuzzy calculus
        Parent parent = new Parent();
        parent.go();

        // creates a new thread of child and starts it
        Child child = new Child(parent);
        child.start();
    }

    private void go() {
        // all sort of initializations
    }

    public void getDataFromChild(int data) {
        // will get data from running child thread
    }
}



public class Child extends Thread {
    private Parent parent;

    // child constructor grabs Parent instance into "o"
    public Child(Parent o) {
        parent = o;
    }

    // this class main loop
    public void run() {
        while(1==1) {
            doSomething();
            try {
                sleep(1000);
            }
            catch(Exception e) { }
        }
    }

    private void doSomething() {
        parent.getDataFromChild(1);
    }

}

Thank you.

Answer 1

Subclassing Thread is considered bad style. It’s better to implement Runnable, and then hand the runnable off to a thread (hmmm… quite analogous to your Parent/Child hand-off!).

Runnable r = new Child(parent);
new Thread(r).start();

Otherwise your Child.java code looks fine to me.

To implement Runnable you just need to provide a run() method:

public class Child implements Runnable {
  private Parent parent;

  public Child(Parent parent) { this.parent = parent; }

  public void run() {
    // what the thread does goes in here...
  }