原型模式

就是实例克隆。利用已有的原型对象，快速的生成原型对象一样的实例。

创建一个实现Clonable 接口的抽象类：

public abstract class Shape implements Cloneable {   private String id;   protected String type;   abstract void draw();   public String getType(){      return type;   }   public String getId() {      return id;   }   public void setId(String id) {      this.id = id;   }   public Object clone() {      Object clone = null;      try {         clone = super.clone();      } catch (CloneNotSupportedException e) {         e.printStackTrace();      }      return clone;   }}

抽象类的实现类：

public class Rectangle extends Shape {   public Rectangle(){     type = "Rectangle";   }   @Override   public void draw() {      System.out.println("Inside Rectangle::draw() method.");   }}public class Square extends Shape {   public Square(){     type = "Square";   }   @Override   public void draw() {      System.out.println("Inside Square::draw() method.");   }}public class Circle extends Shape {   public Circle(){     type = "Circle";   }   @Override   public void draw() {      System.out.println("Inside Circle::draw() method.");   }}

//出去实体类，存入hashmap 中

import java.util.Hashtable;public class ShapeCache {   private static Hashtable<String, Shape> shapeMap       = new Hashtable<String, Shape>();   public static Shape getShape(String shapeId) {      Shape cachedShape = shapeMap.get(shapeId);      return (Shape) cachedShape.clone(); //实体类，自己来克隆   }   // 对每种形状都运行数据库查询，并创建该形状   // shapeMap.put(shapeKey, shape);   // 例如，我们要添加三种形状   public static void loadCache() {      Circle circle = new Circle();      circle.setId("1");      shapeMap.put(circle.getId(),circle);      Square square = new Square();      square.setId("2");      shapeMap.put(square.getId(),square);      Rectangle rectangle = new Rectangle();      rectangle.setId("3");      shapeMap.put(rectangle.getId(),rectangle);   }}

测试：

public class PrototypePatternDemo {   public static void main(String[] args) {      ShapeCache.loadCache();      Shape clonedShape = (Shape) ShapeCache.getShape("1");      System.out.println("Shape : " + clonedShape.getType());              Shape clonedShape2 = (Shape) ShapeCache.getShape("2");      System.out.println("Shape : " + clonedShape2.getType());              Shape clonedShape3 = (Shape) ShapeCache.getShape("3");      System.out.println("Shape : " + clonedShape3.getType());           }}