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From: Cecil Westerhof <Cecil@decebal.nl>
Newsgroups: comp.lang.java.programmer
Subject: Re: What goes wrong with cloning here
Date: Sat, 24 Oct 2015 01:44:40 +0200
Organization: Decebal Computing
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On Saturday 24 Oct 2015 00:51 CEST, Cecil Westerhof wrote:

> On Friday 23 Oct 2015 18:12 CEST, Tassilo Horn wrote:
>
>> Cecil Westerhof <Cecil@decebal.nl> writes:
>>
>>> When I in class A change a field from class B in the clone, the
>>> field in the original is also changed. That should not happen.
>>>
>>> public class A implements Cloneable {
>>> 	private B key;
>>> ^^^
>>> 	public Object clone() throws CloneNotSupportedException {
>>> 		A clone  = (A) super.clone();
>>> 		B newKey = new B();
>>> B oldKey = getKey();
>>>
>>> 		newKey.setA(oldKey.getA());
>>> 		newKey.setB(oldKey.getB());
>>> 		newKey.setC(oldKey.getC());
>>> 		newKey.setD(oldKey.getD());
>>> 		clone.setKey(key);
>> ^^^
>>
>> I guess here you want to set the key of the clone to newKey, not to
>> this.key.
>
> Was an error in my dumbing down. :'-( In the original program it was
> done correctly.
>
>
> I found the problem. It is an application where the class is a JPA
> class. When doing the test (in the original program) with an entity
> that was gotten by a read it goes wrong. When doing it with an
> entity gotten by a new it does what I expect.
>
> Maybe it has to do with the fact that key is the primary key?

For if someone is interested. I rewrote the code. I made the class B
Cloneable again. (Was like this before my first post, but I was
thinking that maybe there went something wrong.) When class B changes
class A does not need to change. Also added hashCode to toString.


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Content-Type: text/x-java-source
Content-Disposition: attachment; filename=A.java

public class A implements Cloneable {
    //public
    public static void main(String[] args) throws CloneNotSupportedException {
        A clone, original;
        B key;

        original = new A();
        key      = new B();
        key.setA("Some text");
        key.setB(12);
        key.setC(73);
        original.setKey(key);
        clone = (A) original.clone();
        clone.getKey().setB(99);
        System.out.println(original.getKey());
        System.out.println(clone.getKey());
    }

	public A() {
	}

	public Object clone() throws CloneNotSupportedException {
		A clone  = (A) super.clone();
        B oldKey = getKey();
		B newKey = (B) oldKey.clone();

		clone.setKey(newKey);

		return clone;
	}

	public B getKey() {
		return key;
	}

	public void setKey(B key) {
		this.key = key;
	}

	public String getC() {
		return c;
	}

	public String getD() {
		return d;
	}

	public void setC(String c) {
		this.c = c;
	}

	public void setD(String d) {
		this.d = d;
	}


    // private
	private B      key;

	private String c;
	private String d;

}

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Content-Type: text/x-java-source
Content-Disposition: attachment; filename=B.java

import java.io.Serializable;
import java.util.Date;

public class B implements Cloneable {
    // public
	public B() {
	}

	public Object clone() throws CloneNotSupportedException {
        return super.clone();
    }

	public String getA() {
		return a;
	}

	public int getB() {
		return b;
	}

	public int getC() {
		return c;
	}

	public Date getD() {
		return d;
	}

	public void setA(String a) {
		this.a = a;
	}

	public void setB(int b) {
		this.b = b;
	}

	public void setC(int c) {
		this.c = c;
	}

	public void setD(Date d) {
		this.d = d;
	}

    public String toString() {
        return String.format("B@%s [a: %s, b: %s, c: %s, d: %s]",
                             Integer.toHexString(hashCode()),
                             a, b, c, d);
    }

    // private
	private String a;
	private int    b;
	private int    c;
	private Date   d;

}

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-- 
Cecil Westerhof
Senior Software Engineer
LinkedIn: http://www.linkedin.com/in/cecilwesterhof

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