Java设计模式之装饰者模式的简单使用

问：装饰者模式有什么用？

答：装饰模式可以在不创造更多子类的情况下，将对象的功能加以扩展。

下面给出一个小例子

1.类图如下：

 Person接口：

package decorator.DIYDecorator;

public interface Person {
    void function();
}

CaiXuKun类：

package decorator.DIYDecorator;

public class CaiXuKun implements Person {
    public void function() {
        System.out.println("CaiXuKun能唱歌");
    }
}

Singer类：

package decorator.DIYDecorator;

public class Singer implements Person {
    public void function() {
        System.out.println("Singer能唱歌");
    }
}

Decorator类：

package decorator.DIYDecorator;

public class Decorator implements Person {
    private Person person;

    public Decorator(Person person) {
        this.person = person;
    }

    @Override
    public void function() {
        person.function();

    }
}

Decorator01类：

package decorator.DIYDecorator;

public class Decorator01 extends Decorator{

    public Decorator01(Person person) {
        super(person);
        // TODO Auto-generated constructor stub
    }
    
    @Override
    public void function() {
        super.function();
        System.out.println("添加额外功能01：跳舞");
    }

}

Decorator02类：

package decorator.DIYDecorator;

public class Decorator02 extends Decorator{

    public Decorator02(Person person) {
        super(person);
        // TODO Auto-generated constructor stub
    }
    
    @Override
    public void function() {
        super.function();
        System.out.println("添加额外功能02：Rap");
        
    }

}

Decorator3类：

package decorator.DIYDecorator;

//虽然没有继承Decorator，但是仍按照装饰器的要求进行书写
public class Decorator3 implements Person{
    private Person person;
    public Decorator3(Person person) {
        this.person=person;
    }
    
    @Override
    public void function() {
        person.function();
        System.out.println("添加额外功能3：打篮球");
        
        if(person instanceof CaiXuKun) {
            System.out.println("===触发终极技能：鸡你太美===");
        }
    }

}

Test测试：

package decorator.DIYDecorator;

public class Test {
    public static void main(String[] args) {
        System.out.println("========装饰器能对实现Person接口的'非装饰器类型的任意类'进行装饰、反复装饰========");
        System.out.println("==========你可以对CaiXuKun类装饰，也可以对Singer类进行装饰============");
//        Person p = new Xxx();
//        Person p = new Singer();
        Person p = new CaiXuKun();
        p.function();
        
        System.out.println("========Decorator01装饰后=========");
        Person p_Dec01 = new Decorator01(p);
        p_Dec01.function();
        
        System.out.println("========Decorator02装饰后=========");
        Person p_Dec02_Dec01 = new Decorator02(p_Dec01);
        p_Dec02_Dec01.function();
        
        System.out.println("========Decorator02单独对p装饰后=========");
        Person p_Dec02=new Decorator02(p);
        p_Dec02.function();
        
        System.out.println("======Decorator3并未继承Decorator，但仍按照其规范书写======");
        System.out.println("========Decorator3单独对p装饰后=========");
        Person p_Dec3 = new Decorator3(p);
        p_Dec3.function();
        
        Person p_Dec01_Dec02_Dec3 = new Decorator3(new Decorator02(new Decorator01(p)));
        System.out.println("========Decorator01,02,3依次对p装饰后=========");
        p_Dec01_Dec02_Dec3.function();
        System.out.println("这里之所以没有触发鸡你太美，是因为触发条件是:当前对象的Person成员变量指向CaiXuKun对象"
                + "而p_Dec01_Dec02_Dec3的当前对象是Decorator3，它的成员变量Person指向Decorator02"
                + "Decorator02的成员变量Person指向Decorator01，Decorator01的成员变量Person才指向CaiXuKun对象");    
    }
}

测试结果：

========装饰器能对实现Person接口的'非装饰器类型的任意类'进行装饰、反复装饰========
==========你可以对CaiXuKun类装饰，也可以对Singer类进行装饰============
CaiXuKun能唱歌
========Decorator01装饰后=========
CaiXuKun能唱歌
添加额外功能01：跳舞
========Decorator02装饰后=========
CaiXuKun能唱歌
添加额外功能01：跳舞
添加额外功能02：Rap
========Decorator02单独对p装饰后=========
CaiXuKun能唱歌
添加额外功能02：Rap
======Decorator3并未继承Decorator，但仍按照其规范书写======
========Decorator3单独对p装饰后=========
CaiXuKun能唱歌
添加额外功能3：打篮球
===触发终极技能：鸡你太美===
========Decorator01,02,3依次对p装饰后=========
CaiXuKun能唱歌
添加额外功能01：跳舞
添加额外功能02：Rap
添加额外功能3：打篮球
这里之所以没有触发鸡你太美，是因为触发条件是:当前对象的Person成员变量指向CaiXuKun对象而p_Dec01_Dec02_Dec3的当前对象是Decorator3，它的成员变量Person指向Decorator02Decorator02的成员变量Person指向Decorator01，Decorator01的成员变量Person才指向CaiXuKun对象