java 装饰模式（大话设计模式）

装饰模式：动态地给一个对象添加一些额外的职责，就增加功能来说，装饰模式比生成子类更为灵活。

装饰模式把每个要装饰的功能放在单独的类中，并让这个类包装它所要装饰的对象，因此，当需要执行特殊行为时，客户代码就可以在运行时根据需要有选择地、按顺序地使用装饰功能包装对象了。

【继承+组合：装饰模式的Decorator类很重要，一方面继承自抽象类Component，另一方面在Decorator抽象类中组合Component对象，通过set方法将相应的Component对象赋值给Decorator中组合的Component对象，Decorator中的operation()操作继承自Component，并且它的方法体内容为：如果Decorator中组合的Component对象非空，执行该Component对象的operation()方法。各个具体的Decorator类中的operation()方法都会先调用父类的operation()方法，以使得Decorator中的operation()操作得以执行，达到层层包装的效果。参考代码理解 】

/**
 * Component是定义一个对象接口，可以给这些对象动态地添加职责
 * 
 * @author liu yuning
 *
 */
public abstract class Component {
    public abstract void operation();
}


/**
 * ConcreteComponent是定义一个具体的对象，也可以给这个对象添加一些职责
 * 
 * @author liu yuning
 *
 */
public class ConcreteComponent extends Component {

    @Override
    public void operation() {
	System.out.println("具体对象的操作");
    }

}
/**
 * Decorator，装饰抽象类，继承了Component，从外类来扩展Component类的功能，但对于Component来说，
 * 是无需知道Decorator的存在的
 * 
 * @author liu yuning
 *
 */
public abstract class Decorator extends Component {
    protected Component component;

    public Component getComponent() {
	return component;
    }

    public void setComponent(Component component) {
	this.component = component;
    }

    @Override
    public void operation() {
	if (component != null) {
	    component.operation();
	}
    }

}

class ConcreteDecoratorA extends Decorator {
    private String addedState;

    @Override
    public void operation() {
	// 首先运行原Component的operation()，再执行本类的功能，如addedState，相当于对原Component进行了装饰
	super.operation();
	addedState = "A中的new state ";
	System.out.println(addedState + "具体装饰对象A的操作");
    }
}

class ConcreteDecoratorB extends Decorator {
    @Override
    public void operation() {
	super.operation();
	addedBehavior();
	System.out.println("具体装饰对象B的操作");
    }

    public void addedBehavior() {
	System.out.print("B中的新增行为 ");
    }
}

class ConcreteDecoratorC extends Decorator {
    @Override
    public void operation() {
	super.operation();
	System.out.println("C没有特殊行为 " + "具体装饰对象C的操作");
    }

}
/**
 * 装饰模式客户端调用代码，装饰的过程更像是层层包装，用前面的对象装饰后面的对象
 * 
 * @author liu yuning
 *
 */
public class DecoratorClient {
    public static void main(String[] args) {
	ConcreteComponent concreteComponent = new ConcreteComponent();
	ConcreteDecoratorA concreteDecoratorA = new ConcreteDecoratorA();
	ConcreteDecoratorB concreteDecoratorB = new ConcreteDecoratorB();
	ConcreteDecoratorC concreteDecoratorC = new ConcreteDecoratorC();

	concreteDecoratorA.setComponent(concreteComponent);
	concreteDecoratorB.setComponent(concreteDecoratorA);
	concreteDecoratorC.setComponent(concreteDecoratorB);
	concreteDecoratorC.operation();

    }
}

案例 穿衣服

/**
 * 装饰模式(Decorator)
 * Person类
 */
public class Person {

    private String name;

    public Person() {}

    public Person(String name) {
        this.name = name;
    }

    public void show() {
        System.out.println("装扮的" + name);
    }

}

/**
 * 装饰模式(Decorator)
 * 服饰类
 */
public class Finery extends Person {

    protected Person component;

    // 打扮
    public void decorate(Person component) {
        this.component = component;
    }

    @Override
    public void show() {
        if (component != null) {
            component.show();
        }
    }

}

class TShirts extends Finery {

    public void show() {
        System.out.print("大T恤  ");
        super.show();
    }

}

class BigTrouser extends Finery {

    public void show() {
        System.out.print("大裤头  ");
        super.show();
    }

}

class Sneakers extends Finery {

    public void show() {
        System.out.print("破球鞋  ");
        super.show();
    }

}

class Suit extends Finery {

    public void show() {
        System.out.print("西装  ");
        super.show();
    }

}

class Tie extends Finery {

    public void show() {
        System.out.print("领带  ");
        super.show();
    }

}

class LeatherShoes extends Finery {

    public void show() {
        System.out.print("皮鞋  ");
        super.show();
    }

}

/**
 * 装饰模式(Decorator)
 * 客户端main方法
 */
public class Attire {

    public static void main(String[] args) {
        Person p0 = new Person("Kobe");
        System.out.println("第一种装扮：");
        TShirts tShirts = new TShirts();
        BigTrouser bigTrouser = new BigTrouser();
        Sneakers sneakers = new Sneakers();
        tShirts.decorate(p0);
        bigTrouser.decorate(tShirts);
        sneakers.decorate(bigTrouser);
        sneakers.show();

        Person p1 = new Person("Allen");
        System.out.println("第二种装扮：");
        Suit suit = new Suit();
        Tie tie = new Tie();
        LeatherShoes leatherShoes = new LeatherShoes();
        leatherShoes.decorate(p1);
        tie.decorate(leatherShoes);
        suit.decorate(tie);
        suit.show();

    }

}