Prototype Pattern

The Prototype pattern’s intent is to specify the kinds of objects that need to be created using a prototypical instance, and to then is able to create new objects by copying this prototype. The copying of objects in Java is typically done by the clone() method of java.lang.Object.

Unlikely, Factory Method and Abstract Factory Method enables client object to create an instance of an appropriate class by invoking a designated method without having to specify the exact concrete class to be instantiated, Prototype pattern offers different more flexible way to achieve the same results.

One of the requirements of the prototype object is that it should provide a way for clients to create a copy of it. By default, all Java objects inherit the builtin clone() method from the topmost java.lang.Object class. The built-in clone() method creates a clone of the original object as a shallow copy.

Shallow copy:

The original top-level object and all of its primitive members are duplicated.
Any lower-level objects that the top-level object contains are not duplicated.
Only references to these objects are copied. This results in both the original and the cloned object referring to the same copy of the lower-level object.

Deep copy:

The original top-level object and all of its primitive members are duplicated.
Any lower-level objects that the top-level object contains are also duplicated.
In this case, both the orginal and the cloned object refer to two different lower-level objects.

Benefits:

It lets you add or remove objects at run time.
It lets you specify new objects by varying its values or structure.
It reduces the need for sub-classing.
It lets you dynamically configure an application with classes.

Applicable Scenarios:

The classes to instantiate are specified at run time.
You need to avoid building a class hierarchy of factories that parallels the hierarchy of objects.
Instances of the class have one of only a few different combinations of state.