总则

• 设计原则：遵循迪米特、单一职责、开闭原则，破坏里氏替换，体现功能复用
• 常用场景：一个类需要动态的添加功能，且这些功能可以相互叠加
• 使用概率：99.99999%
• 复杂度：中
• 变化点：动态添加的功能或者说装饰器
• 选择关键点：添加的功能是否需要动态组装

装饰器模式

• uml类图

  
  
  装饰器模式.PNG

• 代码

  public interface Component {
        void method();
    }

    public class ConcreteComponent implements Component{
        public void method() {
            System.out.println("原来的方法");
        }
    }

    public abstract class Decorator implements Component{
        protected Component component;

        public Decorator(Component component) {
            super();
            this.component = component;
        }

        public void method() {
            component.method();
        }
    }

    public class ConcreteDecoratorA extends Decorator{

        public ConcreteDecoratorA(Component component) {
            super(component);
        }

        public void methodA(){
            System.out.println("被装饰器A扩展的功能");
        }

        public void method(){
            System.out.println("针对该方法加一层A包装");
            super.method();
            System.out.println("A包装结束");
        }
    }

    public class ConcreteDecoratorB extends Decorator{

        public ConcreteDecoratorB(Component component) {
            super(component);
        }

        public void methodB(){
            System.out.println("被装饰器B扩展的功能");
        }

        public void method(){
            System.out.println("针对该方法加一层B包装");
            super.method();
            System.out.println("B包装结束");
        }
    }

    public class Main {

        public static void main(String[] args) {
            Component component =new ConcreteComponent();//原来的对象
            System.out.println("------------------------------");
            component.method();//原来的方法
            ConcreteDecoratorA concreteDecoratorA = new ConcreteDecoratorA(component);//装饰成A
            System.out.println("------------------------------");
            concreteDecoratorA.method();//原来的方法
            concreteDecoratorA.methodA();//装饰成A以后新增的方法
            ConcreteDecoratorB concreteDecoratorB = new ConcreteDecoratorB(component);//装饰成B
            System.out.println("------------------------------");
            concreteDecoratorB.method();//原来的方法
            concreteDecoratorB.methodB();//装饰成B以后新增的方法
            concreteDecoratorB = new ConcreteDecoratorB(concreteDecoratorA);//装饰成A以后再装饰成B
            System.out.println("------------------------------");
            concreteDecoratorB.method();//原来的方法
            concreteDecoratorB.methodB();//装饰成B以后新增的方法
        }
    }