小菜成長記(三)--裝飾者模式

寫一個簡單的角色裝扮代碼：

public class Program {
    public static void main(String[] args) {
        Person person = new Person("小菜");
        System.out.println("第一種裝扮");
        person.wearTShirts();
        person.wearBigTrouser();
        System.out.println("第二種裝扮");
        person.wearSuits();
        person.wearLeaherShoes();
    }
}

class Person{
    private String name;


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

    public void wearTShirts(){
        System.out.println("大T恤 ");
    }

    public void wearBigTrouser(){
        System.out.println("垮褲");
    }

    public void wearSuits(){
        System.out.println("西裝");
    }

    public void wearLeaherShoes(){
        System.out.println("穿皮鞋");
    }
}

問題來了：如果我們增加一個裝飾，就要修改很多代碼，上面的代碼不符合我們的開發閉合原則：面對需求，對程序的改動是通過增加新代碼進行的，而不是更改現有的代碼。

public class Program {
    public static void main(String[] args) {
        Person person = new Person("小菜");
        TShirtsFinery tShirts = new TShirtsFinery();
        BigTrouserFinery bigTrouser = new BigTrouserFinery();
        System.out.println("第一種裝扮");
        tShirts.show();
        bigTrouser.show();

        SuitsFinery suits = new SuitsFinery();
        LeaherShoesFinery leaherShoes = new LeaherShoesFinery();
        System.out.println("第二種裝扮");
        suits.show();
        leaherShoes.show();
    }
}

class Person {
    private String name;

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

abstract class Finery{
    public abstract void show();
}

class TShirtsFinery extends Finery {
    @Override
    public void show() {
        System.out.println("大T恤 ");
    }
}

class BigTrouserFinery extends Finery {
    @Override
    public void show() {
        System.out.println("垮褲 ");
    }
}

class SuitsFinery extends Finery {
    @Override
    public void show() {
        System.out.println("西裝 ");
    }
}

class LeaherShoesFinery extends Finery {
    @Override
    public void show() {
        System.out.println("穿皮鞋 ");
    }
}

問題來了：上面的代碼不夠封閉，我們想要其中一種裝扮，就要暴露很多方法，每個裝飾相互間的聯繫應該封裝起來，我們要採用裝飾設計模式。

public class Program {
    public static void main(String[] args) {
        Person person = new Person("小菜");
        TShirtsFinery tShirts = new TShirtsFinery();
        BigTrouserFinery bigTrouser = new BigTrouserFinery();
        System.out.println("第一種裝扮");
        tShirts.decorate(person);
        bigTrouser.decorate(tShirts);
        bigTrouser.show();

        SuitsFinery suits = new SuitsFinery();
        LeaherShoesFinery leaherShoes = new LeaherShoesFinery();
        System.out.println("第二種裝扮");
        suits.decorate(person);
        leaherShoes.decorate(suits);
        leaherShoes.show();
    }
}
class Person {
    private String name;
    public Person(){ }

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

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

class Finery extends Person{
    protected Person component;
    public void decorate(Person component) {
        this.component = component;
    }

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

class TShirtsFinery extends Finery {
    @Override
    public void show() {
        System.out.println("大T恤 ");
        super.show();
    }
}

class BigTrouserFinery extends Finery {
    @Override
    public void show() {
        System.out.println("垮褲 ");
        super.show();
    }
}

class SuitsFinery extends Finery {
    @Override
    public void show() {
        System.out.println("西裝 ");
        super.show();
    }
}

class LeaherShoesFinery extends Finery {
    @Override
    public void show() {
        System.out.println("穿皮鞋 ");
        super.show();
    }
}

個人總結；裝飾模式是爲已有功能動態地添加更多功能的一種方式。什麼時候用呢？當系統需要新功能的時候，是向舊的類中添加新的代碼。這些新加的代碼通常裝飾了原有類的核心職責或主要行爲。