设计模式(6)

创建型模式-原型模式

介绍

用原型实例指定创建对象的种类，并且通过拷贝这些原型创建新的对象。

实例

• 创建一个实现了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;
     }
  }

• 创建扩展了上面抽象类的实体类。

  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.");
     }
  }

• 创建一个类，从数据库获取实体类，并把它们存储在一个Hashtable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();
     }
   
     // 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);
     }
  }

• PrototypePatternDemo使用ShapeCache类来获取存储在 Hashtable中的形状的克隆。

  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());        
     }
  }

• 输出结果

  Shape : Circle
  Shape : Square
  Shape : Rectangle

总结

这种模式是实现了一个原型接口，该接口用于创建当前对象的克隆。当直接创建对象的代价比较大时，则采用这种模式。

参考

菜鸟教程