设计模式 -- 装饰器模式（Decorator Pattern）

装饰器模式：属于结构型模式，作为现有的类的一个包装，向一个现有的对象添加新的功能，同时又不改变其结构。

介绍

• 意图：动态地给一个对象添加一些额外的职责。就增加功能来说，装饰器模式相比生成子类更为灵活
• 主要解决问题：在不想增加很多子类的情况下扩展类
• 优点：装饰类和被装饰类可以独立发展，不会相互耦合
• 缺点：多层装饰比较复杂

示例

为矩形、圆形装 饰边框为例

//创建一个接口
public interface Shape {
    void draw();
}

//实现接口的实体类。

public class Rectangle implements Shape {

    @Override
    public void draw() {
        System.out.println("Shape: Rectangle");
    }
}

public class Circle implements Shape {

    @Override
    public void draw() {
        System.out.println("Shape: Circle");
    }
}


//实现Shape接口的抽象装饰类

public abstract class ShapeDecorator implements Shape {

    protected Shape decoratedShape;

    public ShapeDecorator(Shape decoratedShape){
        this.decoratedShape = decoratedShape;
    }

    public void draw(){
        decoratedShape.draw();
    }
}

//扩展ShapeDecorator类的实体装饰类

public class RedShapeDecorator extends ShapeDecorator {
    
    public RedShapeDecorator(Shape decoratedShape) {
        super(decoratedShape);
    }
    
    @Override
    public void draw() {
        decoratedShape.draw();
        setRedBorder(decoratedShape);
    }
    
    private void setRedBorder(Shape decoratedShape){
        System.out.println("Border Color: Red");
    }
}

//使用
public static void main(String[] args) {
    Shape circle = new Circle();
    Shape redCircle = new RedShapeDecorator(new Circle());
    Shape redRectangle = new RedShapeDecorator(new Rectangle());
    System.out.println("Circle with normal border");
    circle.draw();
    System.out.println("\nCircle of red border");
    redCircle.draw();
    System.out.println("\nRectangle of red border");
    redRectangle.draw();
}