Calling super()

Question

When do you call super() in Java? I see it in some constructors of the derived class, but isn\'t the constructors for each of the parent class called automatically? Why woul

Answer 1

I wanted to provide some information that hasn't been mentioned so far. If you use a call to this(...) in a constructor, then you can't have a call to super(...); This also includes Java's automatic insertion of the parameterless call to super();

The following example illustrates this point, including explanatory comments:

public class B extends A {
    private int x;

    public B() {
        // Java doesn't call super(); here, because 
        // of the call to this(...); below.
        // You can't call super(...) here either,
        // for the same reason.

        this(42);  // Calls public B(int x) below.
    }

    public B(int x) {
        // Java does call super(); here.
        // You can call super(...) here, if you want/need to.
        // The net result of calling new B() above is that
        // super(...) for class A only gets called once.

        this.x = x;
    }
}