Prototype Pattern

Tags
Design Pattern, Java

Introduction

• Purpose
  • Create objects based upon a template of an existing objects through cloning.
• Use When
  • Composition, creation, and representation of objects should be decoupled from a system
  • Classes to be created are specified at runtime.
  • Objects or object structures are required that are identical or closely resemble other existing objects or object structures.
  • The initial creation of each object is an expensive operation.
  • When to avoid building a class hierarchy of factories that parallels the class hierarchy of products

Characteristics

• Advantage
  • Hides concrete product classes from clients
  • Decouples the clients from the creational process
• Prototypes can be supplied and changed at runtime
• The client asks the prototype to clone itself for a new object of the prototype.
• It provides great flexibility in configuring and changing a program at runtime
  • Adding and removing products at run-time
  • Reduced subclassing
  • Configuring an application with classes dynamically
    • Loading the classes dynamically

Participants

• Prototype
  • Defines the interface (an operation) of cloning itself.
• ConcreteProducts
  • Concrete objects that can clone themselves.
• Client
  • Obtain more objects by asking them to clone themselves.

How to Use (Example)

• Java’s Cloneable

  class Stack implements Cloneable {
      private final int maxSize;
      private int top;
      private Object[] store;
  
      public Stack (int size) {
          maxSize = size;
          store = new Object[size];
          top = -1;
      }
  
      public Object clone() throws CloneNotSupportedException {
          Stack result;
          try {
              result = (Stack) super.clone();
              result.store = (Object[]) store.clone();
              return result;
          } catch (CloneNotSupportedException e) {
              return null;
          }
      }
  }