What does it mean to clone() an object?

Question

What is object cloning in vb6 or java? In what situation do we use a clone? What does cloning objects mean? Can any one tell me with example please.

Answer 1

Cloning is actually copying the object data into a new object.

This example doesn't clone the data:

Foo p = new Foo();
Foo o = p;

If Foo has a member a and you change p.a then o.a also changes because both p and o point to the same object.

However,

Foo p = new Foo();
Foo o = p.Clone();

In this case if you change p.a then o.a remains the same because they actually point to separate objects.

There are actually two different ways you can clone: shallow clone or deep clone.

A shallow clone just makes a new object and copies the members into the new object. This means that if one of the members is actually a pointer to another object then that object will be shared between the old object and new object.

A deep clone actually goes through and clones all the members into the new object. That way the objects are complete copies of all the data.

Answer 2

Generaly speaking objects are passed by reference. So if you say $objB=$objA you are not getting a new object; you are getting a new name for the same object. However, if you say $objB= clone $objA you get a copy of $objA. In the first case, whatever you do to $objB also happens to $objA. In the 2nd case, $objB is independent.