定义

原型是一种创建型设计模式， 使你能够复制对象， 甚至是复杂对象， 而又无需使代码依赖它们所属的类。

所有的原型类都必须有一个通用的接口， 使得即使在对象所属的具体类未知的情况下也能复制对象。 原型对象可以生成自身的完整副本， 因为相同类的对象可以相互访问对方的私有成员变量。

简单来说就是在类上面实现一个clone方法，使其能够管理自身对象的复制功能。

结构

伪代码

示例

复制图形

1. 定义通用形状接口: prototype.Shape.java

package prototype;

public abstract class Shape {

    public int x;

    public int y;

    public String color;

    public Shape() {
    }

    public Shape(Shape target) {
        if (target != null) {
            this.x = target.x;
            this.y = target.y;
            this.color = target.color;
        }
    }

    public abstract Shape clone();


    public boolean equals(Object object) {
        if (!(object instanceof Shape)) return false;
        Shape shape = (Shape) object;
        return shape.x == this.x && shape.y == this.y && shape.color.equals(this.color);
    }

}

2. 简单形状: prototype.Circle.java

package prototype;

public class Circle extends Shape {

    public int radius;

    public Circle() {

    }

    public Circle(Circle target) {
        super(target);
        if (target != null) {
            this.radius = target.radius;
        }
    }

    @Override
    public Shape clone() {
        return new Circle(this);
    }

    @Override
    public boolean equals(Object object) {
        if (!(object instanceof Circle) || !super.equals(object)) return false;
        Circle circle = (Circle) object;
        return circle.radius == this.radius;
    }

}

3. 另一个形状: prototype.Rectangle.java

package prototype;

public class Rectangle extends Shape {

    public int width;

    public int height;

    public Rectangle() {

    }

    public Rectangle(Rectangle target) {
        super(target);
        if (target != null) {
            this.width = target.width;
            this.height = target.height;
        }
    }

    @Override
    public Shape clone() {
        return new Rectangle(this);
    }

    @Override
    public boolean equals(Object object) {
        if (!(object instanceof Rectangle) || !super.equals(object)) return false;
        Rectangle rectangle = (Rectangle) object;
        return rectangle.width == this.width && rectangle.height == this.height;
    }
}

4. 克隆示例: prototype.Demo.java

package prototype;

import java.util.ArrayList;
import java.util.List;

public class Demo {

    public static void main(String[] args) {
        List<Shape> shapes = new ArrayList<Shape>();
        List<Shape> shapesCopy = new ArrayList<Shape>();

        Circle circle = new Circle();
        circle.x = 10;
        circle.y = 20;
        circle.radius = 5;
        circle.color = "red";
        shapes.add(circle);


        Circle anotherCircle = (Circle) circle.clone();
        shapes.add(anotherCircle);

        Rectangle rectangle = new Rectangle();
        rectangle.width = 10;
        rectangle.height = 20;
        rectangle.color = "blue";
        shapes.add(rectangle);

        cloneAndCompare(shapes, shapesCopy);

    }

    private static void cloneAndCompare(List<Shape> shapes, List<Shape> shapesCopy) {
        for (Shape shape :
                shapes) {
            shapesCopy.add(shape.clone());
        }
        for (int i = 0; i < shapes.size(); i++) {
            if (shapes.get(i) != shapesCopy.get(i)) {
                System.out.println(i + ": Shapes are different objects (yay!)");
                if (shapes.get(i).equals(shapesCopy.get(i))) {
                    System.out.println(i + ": And they are identical (yay!)");
                } else {
                    System.out.println(i + ": But they are not identical (booo!)");
                }
            } else {
                System.out.println(i + ": Shape objects are the same (booo!)");
            }
        }
    }

}

5. 输出结构

0: Shapes are different objects (yay!)
0: And they are identical (yay!)
1: Shapes are different objects (yay!)
1: And they are identical (yay!)
2: Shapes are different objects (yay!)
2: And they are identical (yay!)