再说装饰器模式

To extend or modify the behaviour of an instance at runtime decorator design pattern is used. Inheritance is used to extend the abilities of a class. Unlike inheritance, you can choose any single object of a class and modify its behaviour leaving the other instances unmodified.

这是我们生活中一种常见的美味，其制作过程就是一种典型的装饰器模式，除了原味，我们可以额外添加坚果、草莓等额外的美味，同时还保持了原有冰淇淋的美味。

装饰器模式的UML类图

• 定义冰淇淋制作接口Icecream

public interface Icecream {    String makeIcecream();}

• 原味冰淇淋：SimpleIcecream

public class SimpleIcecream implements Icecream {  @Override  public String makeIcecream() {    return "Base Icecream";  }}

• 冰淇淋装饰器抽象类

abstract public class IcecreamDecorator implements Icecream {    protected Icecream specialIcecream;    public IcecreamDecorator(Icecream specialIcecream) {        this.specialIcecream = specialIcecream;    }    public String makeIcecream() {        return specialIcecream.makeIcecream();    }}

• 坚果冰淇淋装饰

public class NuttyDecorator extends IcecreamDecorator {    public NuttyDecorator(Icecream specialIcecream) {        super(specialIcecream);    }    public String makeIcecream() {        System.out.println("NuttyDecorator makeIcecream");        return specialIcecream.makeIcecream() + addNuts();    }    private String addNuts() {        return " + cruncy nuts";    }}

• 草莓冰淇淋装饰

public class StrawberryDecorator extends IcecreamDecorator {    public StrawberryDecorator(Icecream specialIcecream) {        super(specialIcecream);    }    public String makeIcecream() {        System.out.println("StrawberryDecorator makeIcecream");        return super.makeIcecream() + " + strawberry";    }}

• 可爱甜心冰淇淋装饰

public class HoneyDecorator extends IcecreamDecorator {    public HoneyDecorator(Icecream specialIcecream) {        super(specialIcecream);    }    public String makeIcecream() {        System.out.println("HoneyDecorator makeIcecream");        return specialIcecream.makeIcecream() + addHoney();    }    private String addHoney() {        return " + sweet honey";    }}

• 最后我们来制作一个多味的冰淇淋，同时添加了坚果、草莓与可爱甜心

public class TestDecorator {    public static void main(String args[]) {        Icecream icecream = new StrawberryDecorator(new HoneyDecorator(new NuttyDecorator(new SimpleIcecream())));        System.out.println(icecream.makeIcecream());    }}

https://javapapers.com/design-patterns/decorator-pattern/