Question

I am having a base class C with fields X, Y and Z.

C1 extends C and is having an extra field, T.

In the C1 constructor, I do call the super (C) constructor with some hard coded values for the fields X, Y and Z. Then I set T.

Are there any patterns to automatically validate all the fields of C1 by doing something in the C constructor ? So I am trying to push the automatic validation to the base class.

Please note that calling the super constructor should be done before any statement in the C1 constructor. I started with some abstract validate() method, but I am not I am on the right track.

Thanks.

Answer 1

I would say that the super class should validate itself. An object needs to enforce its own contract. Any validation of C’s values should be done in its own constructor. Likewise, the subclass should validate itself.

public class A {
    private int x;

    public A(int x) {
        if (x < 0) throw new IllegalArgumentException("x cannot be negative");
        this.x = x;
    }
}

public class B extends A {
    private String y;

    public B(int x, String y) {
        super(x);
        if (y == null) throw new IllegalArgumentException("y cannot be null");
        this.y = y;
    }
}