public interface IDoThings {

    public void doSomeThing();

} 

public class DoThings implements IDoThings {

    @Override

    public void doSomeThing() {

        System.out.println("做一些事情");

    }

}

public class Decorator implements IDoThings {

    private IDoThings beverage;

    Decorator(IDoThings beverage){

        this.beverage =beverage;

    }

    @Override

    public void doSomeThing() {

        beverage.doSomeThing();

    }

}

public class Eat extends Decorator{

    Eat(IDoThings beverage){

        super(beverage);

    }

    @Override

    public void doSomeThing() {

        super.doSomeThing();

        System.out.println("吃饭");

    }

}

public class Run extends Decorator{

    Run(IDoThings beverage){

        super(beverage);

    }

    @Override

    public void doSomeThing() {

        super.doSomeThing();

        System.out.println("跑步");

    }

}

public class TestDecorator {

     public static void main(String[] args) {

            IDoThings instance = new DoThings();

            instance = new Eat(instance);

            instance = new Run(instance);

            instance.doSomeThing();

        }

}