Java clone() method

Question

I read Effective Java by J.Bloch and here was wrote:

If you design a class for inheritance, be aware that if you choose not to provide a well-behave

Answer 1

In your case yes you can override clone():

public class A {
}

public class B extends A implements Cloneable {

    @Override
    public B clone() throws CloneNotSupportedException {
        return (B) super.clone();
    }
}

and still have an effective clone mechanism - you are therefore telling the truth when you state implements Cloneable.

However, all that is needed to break that promise is to give A a private variable.

public class A {
    private int a;
}

and now your promise is broken - unless A implements clone, in which case you can use super.clone():

public class A {

    private int a;

    @Override
    public A clone() throws CloneNotSupportedException {
        A newA = (A) super.clone();
        newA.a = a;
        return newA;
    }
}

public class B extends A implements Cloneable {

    private int b;

    @Override
    public B clone() throws CloneNotSupportedException {
        B newB = (B) super.clone();
        newB.b = b;
        return newB;
    }
}

Essentially - as Joshua Bloch states - if you don't implement clone your sub-classes also cannot (generally).