Java设计模式——原型模式

原型模式是一种创建模式，它在考虑性能的同时创建重复对象。
当直接创建对象成本高时，使用原形模式。它定义一个原型接口，这个接口会帮助返回克隆对象。
例如，一个对象将在一个代价高昂的数据库操作之后创建。我们可以缓存对象，在下一次请求时返回其克隆，并在需要时更新数据库，从而减少数据库调用。

举例说明：

1. 创建一个抽象类Shape以及它的子类（Circle、Rectangle、Square）;
2. 创建ShapeCache类，它将shape对象存放在哈希表中，并在得到请求时返回一个克隆对象。

1、创建抽象类Shape，需要实现Clonable接口

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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;    } }

2、创建子类

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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.");    } }

3、创建ShapeCache类，用于将对象存放到哈希表中

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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();    }      // for each shape run database query and create shape    // shapeMap.put(shapeKey, shape);    // for example, we are adding three shapes         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);    } }

4、通过ShapeCache，返回克隆对象

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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());         } }

5、结果

Shape : Circle
Shape : Square
Shape : Rectangle