介绍

装饰模式，可称为装饰器模式或修饰模式，是面向对象编程领域中，一种动态地往一个类中添加新的行为的设计模式。在原有的基础上进行功能增强。就功能而言，装饰模式相比生成子类更为灵活，这样可以给某个对象而不是整个类添加一些功能。特点是用来增强原有对象功能，依附于原有对象。应用在用于需要对原有对象增加功能而不是完全覆盖的场景。

角色

角色	说明
Component	抽象构件
ConcreteComponent	具体构件
Decorator	抽象装饰类
ConcreteDecorator	具体装饰类

角色示例

类名	担任角色	说明
Soldier	Component	士兵
LandSoldier	ConcreteComponent	陆军
SeaSoldier	ConcreteComponent	海军
SoldierArsenal	Decorator	士兵军火库
M4a1	ConcreteDecorator	M4a1枪支
Ak47	ConcreteDecorator	Ak47枪支

UML类图

代码

abstract class Soldier {
    String weapon = "no weapon";

    public String getWeapon(){
        return weapon;
    }
}

class LandSoldier extends Soldier {
    public LandSoldier() {
        weapon = "+LandSoldier";
    }
}

class SeaSoldier extends Soldier {
    public SeaSoldier() {
        weapon = "+SeaSoldier";
    }
}

abstract class SoldierArsenal extends Soldier {
    public abstract String getWeapon();
}

class M4a1 extends SoldierArsenal {

    private Soldier soldier;

    public M4a1(Soldier s) {
        soldier = s;
    }

    @Override
    public String getWeapon() {
        return soldier.getWeapon() + "+with M4a1";
    }

}

class Ak47 extends SoldierArsenal {
    
    private Soldier soldier;

    public Ak47(Soldier s) {
        soldier = s;
    }

    @Override
    public String getWeapon() {
        return soldier.getWeapon() + "+with Ak47";
    }

}

public class SoldierTest {
    public static void main(String[] args) {
        Soldier s1 = new LandSoldier();
        System.out.println(s1.getWeapon());

        M4a1 s2 = new M4a1(s1);
        System.out.println(s2.getWeapon());

        Ak47 s3 = new Ak47(s2);
        System.out.println(s3.getWeapon());
    }
}

创建 SoldierTest.java，内容如上。

执行

$ javac SoldierTest.java
$ java SoldierTest
+LandSoldier
+LandSoldier+with M4a1
+LandSoldier+with M4a1+with Ak47