Cloning (programming): Difference between revisions

Revision as of 07:16, 17 June 2007

Revision as of 08:26, 5 November 2007

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Copying primitive types in Java:

<source lang="java">

<pre>

int original = 42;

int copy = 0;

copy = original;

</presource>

Many OOP programming languages (including Java, [[C Sharp|C#]], [[D (programming language)|D]], [[ECMAScript]]) make use of object references. Object references, which are similar to pointers in other languages, allow for objects to be passed around by [[Pointer (computing)|address]] so that the whole object need not be copied.

A Java example, when "copying" an object using simple assignment:

<source lang="java">

<pre>

Object original = new Object();

Object copy = null;

copy = original; // does not copy object, only copies its reference

</presource>

The object is not duplicated, the variables 'original' and 'copy' are actually referring to the same object.

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Cloning an object in Java:

<source lang="java">

<pre>

Object original = new Object();

Object copy = null;

copy = original.clone(); // duplicates the object and assigns the new reference to 'copy'

</presource>

C++ objects in general behave like primitive types, so to copy a C++ object one could use the '=' (assignment) operator. There is a default assignment operator provided for all classes, but its effect may be altered through the use of [[operator overloading]]. There are dangers when using this technique (see [[Slicing]]). A method of avoiding slicing can be implementing a similar solution to the Java clone() method for your classes, and using pointers. (Note that there is no built in clone() method)

A C++ example of object cloning:

<source lang="cpp">

<pre>

Object original;

Object copy;

copy = original; // copies the contents of original into copy

</presource>

A C++ example of object cloning using pointers (avoids slicing):

<source lang="cpp">

<pre>

Object * original = new Object;

Object * copy = NULL;

copy = original.->clone(); // creates a copy of original and assigns its address to copy

</presource>

[[Category:Object-oriented programming]]