How to clone/copy an instance of my own class?

Question

Is this way of using clone correct? I am getting a runtime error every time. Also can anybody suggest a way to write copy constructor in this class?

public class Pair {
    final StringBuffer x;
    final StringBuffer y;

    public Pair(StringBuffer x, StringBuffer y) {
        this.x = x;
        this.y = y;
    }

    public StringBuffer getX() {
        return x;
    }

    public StringBuffer getY() {
        return y;
    }

    public Pair clone() {
        Pair p = new Pair(new StringBuffer(), new StringBuffer());
        try {
            p = (Pair) super.clone();
        } catch (CloneNotSupportedException e) {
            throw new Error();
        }
        return p;
    }
}

Why do you have a copy constructor, when you ignore what it does? — Tom, May 31 '16 at 10:41

score 3 · Accepted Answer · answered May 31 '16 at 10:31

A copy constructor:

public Pair(Pair other) {
  this.x = new StringBuffer(other.x.toString());
  this.y = new StringBuffer(other.y.toString());
}

You should avoid using clone():

clone is very tricky to implement correctly in all circumstances, nearly to the point of being pathological

the importance of copying objects will always remain, since object fields often need to be defensively copied

copy constructors and static factory methods provide an alternative to clone, and are much easier to implement

In addition, the native implementation of `clone` will only give you a shallow copy. — Stephen C, May 31 '16 at 12:17

How to clone/copy an instance of my own class?

1 Answers1