装饰器模式（Decorator）

装饰器模式

一.装饰器模式

1.1 定义

• 在不改变原类文件和使用继承的情况下，动态的扩展一个对象的功能.
• 通过创建一个包装对象（装饰），来包裹真实的对象.

二.具体实现

1.1 创建被装饰对象接口

    public interface IDecorated {
        void print();
    }

1.2 创建被装饰对象

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

1.3 创建装饰器抽象类

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

1.4 创建具体装饰器

    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 调用

    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 输出

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

三.优缺点

3.1 优点

• 装饰器模式和继承的共同特点就是扩展对象的功能，而装饰器模式比继承更加灵活.
• 通过使用不同的具体装饰器类，及其不同的排列组合，可以产生出大量不同的组合.

3.2 缺点

• 装饰器模式比继承更加复杂.
• 会出现一些小类，过度使用会使程序变得复杂.

四.源码

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

END