设计模式详解（二）原型模式

文章目录

• • 1. 概念
  • 2. 代码示例

1. 概念

2. 代码示例

场景：根据一辆BMW汽车模型再创建出多辆BMW

package designpattern;

class Wheel{//轮子类
	double price;//轮子价格

	public Wheel(double price) {
		super();
		this.price = price;
	}

	@Override
	public String toString() {
		return "Wheel [price=" + price + "]";
	}
	
	
}
class Car implements Cloneable{
	String name;//汽车名称
	Wheel wheel;//汽车轮子
	@Override
	protected Car clone() throws CloneNotSupportedException {
		
		return (Car) super.clone();
	}

	public Car(String name, Wheel wheel) {
		super();
		this.name = name;
		this.wheel = wheel;
	}

	@Override
	public String toString() {
		return "Car [name=" + name + ", wheel=" + wheel + "]";
	}
	

}
public class PrototypeDemo {
	static Car carProtoType=new Car("BMW",new Wheel(100));
	public static void main(String[] args) throws CloneNotSupportedException {
		Car[] cars=new Car[3];
		for(int i=0;i<3;i++)
		{
			cars[i]=carProtoType.clone();
			System.out.println(cars[i]);
		}
		System.out.println("-------------");
		cars[0].wheel.price=200;
		for(int i=0;i<3;i++)
		{
			System.out.println(cars[i]);
		}
		System.out.println(cars[0]==cars[1]);
		System.out.println(cars[0].wheel==cars[1].wheel);
	}
}

上面代码中在Car类中重写了Object类中的clone方法，通过该方法可以调用该方法的对象的一个副本，省去了由类而生的再造过程

从运行结果来看，的却得到了3个副本，但是存在一个问题，只要修改了其中一辆车的轮胎价格，其他车的轮胎价格也会改变

		System.out.println(cars[0]==cars[1]);//false
		System.out.println(cars[0].wheel==cars[1].wheel);//true

从这两条输出语句可以看出，3辆车的轮胎引用指向的是一个对象，这就是浅拷贝

浅拷贝：基本类型的值会被赋值，引用类型的值也只是拷贝了引用的副本，所以这些引用的副本指向的对象都是同一个

代码修改如下：

package designpattern;



class Wheel implements Cloneable{//轮子类
	double price;//轮子价格

	public Wheel(double price) {
		super();
		this.price = price;
	}

	@Override
	public String toString() {
		return "Wheel [price=" + price + "]";
	}

	@Override
	protected Wheel clone() throws CloneNotSupportedException {
		
		return (Wheel) super.clone();
	}
	
	
	
}
class Car implements Cloneable{
	String name;//汽车名称
	Wheel wheel;//汽车轮子
	@Override
	protected Car clone() throws CloneNotSupportedException {
		
		Car car=(Car) super.clone();
		car.wheel=this.wheel.clone();;
		return car;
	}

	public Car(String name, Wheel wheel) {
		super();
		this.name = name;
		this.wheel = wheel;
	}

	@Override
	public String toString() {
		return "Car [name=" + name + ", wheel=" + wheel + "]";
	}
	

}
public class PrototypeDemo {
	static Car carProtoType=new Car("BMW",new Wheel(100));
	public static void main(String[] args) throws CloneNotSupportedException {
		Car[] cars=new Car[3];
	
		
		for(int i=0;i<3;i++)
		{
			cars[i]=carProtoType.clone();
			System.out.println(cars[i]);
		}
		System.out.println("-------------");
		cars[0].wheel.price=200;
		for(int i=0;i<3;i++)
		{
			System.out.println(cars[i]);
		}
		System.out.println(cars[0]==cars[1]);
		System.out.println(cars[0].wheel==cars[1].wheel);
	}
}

修改之后对wheel引用的拷贝是深拷贝