什么是装饰者模式
装饰模式是在不使用继承和不改变原类文件的情况下，动态的扩展一个对象的功能。
组成结构
1.Component（抽象组件又叫被装饰对象的基类）
2.ConcreteComponent（具体组件又叫具体被装饰对象）
3. Decorator（装饰者抽象类）
4.ConcreteDecorator（具体装饰者）
假设一个场景
在学校门口有一个卖煎饼的早餐车，主要是卖煎饼，可以加鸡蛋，加香肠。现在来了一位顾客，需要煎饼+鸡蛋+香肠
一般实现
package com.design.mode.decorate;
public class Origin {
public interface Cake {
public String getDescription();
public int cost();
}
public static class PanCake implements Cake{
@Override
public String getDescription() {
return "煎饼";
}
@Override
public int cost() {
return 1;
}
}
public static class Egg implements Cake{
@Override
public String getDescription() {
return "鸡蛋";
}
@Override
public int cost() {
return 5;
}
}
public static class Sausage implements Cake{
@Override
public String getDescription() {
return "煎饼";
}
@Override
public int cost() {
return 3;
}
}
public static void main(String[] args) {
PanCake panCake = new PanCake();
Egg egg = new Egg();
Sausage sausage = new Sausage();
String description = panCake.getDescription() + "+" + egg.getDescription() + "+" + sausage.getDescription();
int cost = panCake.cost() + egg.cost() + sausage.cost();
System.out.println(description);
System.out.println(cost);
}
}
根据以上代码，
最终早餐的描述=panCake.getDescription() + egg.getDescription() + sausage.getDescription()
最终早餐的花费=panCake.cost() + egg.cost() + sausage.cost()
如果新增要再加一个鸡蛋，那么早餐的描述和花费都得修改
使用装饰者模式
类结构
代码
package com.design.mode.decorate;
public class DecorateMode {
public interface Cake{
public String getDescription();
public int cost();
}
/**
* 煎饼类，也是被装饰者
*/
public static class PanCake implements Cake{
@Override
public String getDescription() {
return "煎饼";
}
@Override
public int cost() {
return 1;
}
}
public static abstract class Decorator implements Cake{
private Cake cake;
public Decorator(Cake cake) {
this.cake = cake;
}
@Override
public String getDescription() {
return cake.getDescription();
}
@Override
public int cost() {
return cake.cost();
}
}
public static class EggDecorator extends Decorator{
public EggDecorator(Cake cake) {
super(cake);
}
@Override
public String getDescription() {
return super.getDescription() + "+" + "鸡蛋";
}
@Override
public int cost() {
return super.cost() + 5;
}
}
public static class SausageDecorator extends Decorator{
public SausageDecorator(Cake cake) {
super(cake);
}
@Override
public String getDescription() {
return super.getDescription() + "+" + "香肠";
}
@Override
public int cost() {
return super.cost() + 3;
}
}
public static void main(String[] args) {
PanCake panCake = new PanCake();
SausageDecorator sausageDecorator = new SausageDecorator(panCake);
EggDecorator eggDecorator = new EggDecorator(sausageDecorator);
System.out.println(eggDecorator.getDescription());
System.out.println(eggDecorator.cost());
}
}
优点：在不变动原类方法的情况下，对功能进行了拓展，如果再加一个鸡蛋，只需要在原早餐上在进行鸡蛋修饰就行，方法不用变动。
