裝飾器模式（Decorator）

裝飾器模式

一.裝飾器模式

1.1 定義

• 在不改變原類文件和使用繼承的狀況下，動態的擴展一個對象的功能.
• 經過建立一個包裝對象（裝飾），來包裹真實的對象.

二.具體實現

1.1 建立被裝飾對象接口

public interface IDecorated {
        void print();
    }

1.2 建立被裝飾對象

public class Decorated implements IDecorated{
        @Override
        public void print() {
            System.out.println("decorated print ...");
        }
    }

1.3 建立裝飾器抽象類

public abstract class Decorator implements IDecorated {
        private IDecorated decorated;
        public Decorator(IDecorated decorated){
            this.decorated = decorated;
        }
        public void print(){
            decorated.print();
        }
    }

1.4 建立具體裝飾器

public class DecoratorA extends Decorator{
        public DecoratorA(IDecorated decorated){
            super(decorated);
        }
        @Override
        public void print() {
            super.print();
            System.out.println("decoratorA print ...");
        }
    }
    public class DecoratorB extends Decorator{
        public DecoratorB(IDecorated decorated){
            super(decorated);
        }
        @Override
        public void print() {
            super.print();
            System.out.println("decoratorB print ...");
        }
    }

1.5 調用

public static void main(String[] args) {
        IDecorated decorated = new Decorated();
        Decorator decorator = new DecoratorA(decorated);
        decorator.print();
        decorator = new DecoratorB(new DecoratorA(decorated));
        decorator.print();
    }

1.6 輸出

decorated print ...
    decoratorA print ...
    decorated print ...
    decoratorA print ...
    decoratorB print ...

三.優缺點

3.1 優勢

• 裝飾器模式和繼承的共同特色就是擴展對象的功能，而裝飾器模式比繼承更加靈活.
• 經過使用不一樣的具體裝飾器類，及其不一樣的排列組合，能夠產生出大量不一樣的組合.

3.2 缺點

• 裝飾器模式比繼承更加複雜.
• 會出現一些小類，過分使用會使程序變得複雜.

四.源碼

https://github.com/Seasons20/DisignPattern.git

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