装饰者模式

http://lgbolgger.iteye.com/blog/2154368 

有时候为了传承某个类的一些功能，我们可以采用继承该类来获取功能，并可以通过覆写某些方法来进行功能加强。然而若想对一批类的功能进行加强，如果仍采用继承，不仅在代码上重复，并且不利于扩展。

public interface Component {

    public void  fun();
}

public class ConcreteAComponent implements Component{

    @Override
    public void fun() {
        System.out.println("ConcreteAComponent");
    }

}

public class ConcreteBComponent implements Component{

    @Override
    public void fun() {
        System.out.println("ConcreteBComponent");
    }

}

如果采用继承的话，加强ConcreteAComponent，则需要写一个类继承ConcreteAComponent，加强ConcreteBComponent，则需要写一个类继承ConcreteBComponent，就会造成每当要加强一个类时就必须要新建一个类继承它，在代码上造成严重的重复。

ConcreteTimeDecorator 针对的是接口Component ，不依赖于任何一个具体的Component ，所以每当要增强一个具体的Component时，不用再添加新的类，和继承就不一样了，这样更加容易扩展。

public class ConcreteTimeDecorator implements Component{
    
    private Component component;

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

    @Override
    public void fun() {
        long start=System.currentTimeMillis();
        System.out.println("start at "+start);
        component.fun();
        long end=System.currentTimeMillis();
        System.out.println("end at "+end+",cost "+(end-start));
    }

}

public class ConcretePrintDecorator implements Component{

    private Component component;

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

    @Override
    public void fun() {
        System.out.println("before real component run");
        component.fun();
        System.out.println("after real component run");
    }

}

ConcreteAComponent concreteAComponent=new ConcreteAComponent();
        
        ConcreteTimeDecorator concreteTimeDecorator=new ConcreteTimeDecorator(concreteAComponent);
        concreteTimeDecorator.fun();
        
        System.out.println("--------------------------------------------");
        ConcretePrintDecorator concretePrintDecorator=new ConcretePrintDecorator(concreteAComponent);
        concretePrintDecorator.fun();

 装饰器类与Component类紧耦合