裝飾器模式允許用戶在不改變其結(jié)構(gòu)的情況下向現(xiàn)有對(duì)象添加新功能。這種類型的設(shè)計(jì)模式屬于結(jié)構(gòu)模式，因?yàn)檫@種模式充當(dāng)現(xiàn)有類的包裝器。

此模式創(chuàng)建了一個(gè)裝飾器類，它包裝了原始類并提供了保持類方法簽名完整的附加功能。

我們通過以下示例演示裝飾器模式的使用，在該示例中我們將使用某種顏色裝飾形狀而不更改形狀類。

執(zhí)行

我們將創(chuàng)建一個(gè)Shape接口和實(shí)現(xiàn)Shape接口的具體類。然后我們將創(chuàng)建一個(gè)抽象裝飾器類ShapeDecorator實(shí)現(xiàn)Shape接口并將Shape對(duì)象作為其實(shí)例變量。

RedShapeDecorator是實(shí)現(xiàn)ShapeDecorator的具體類。

DecoratorPatternDemo，我們的演示類將使用RedShapeDecorator來裝飾Shape對(duì)象。

步驟1

創(chuàng)建一個(gè)接口。

形狀.java

public interface Shape {
   void draw();
}

第2步

創(chuàng)建實(shí)現(xiàn)相同接口的具體類。

矩形.java

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

圈子.java

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

步驟 3

創(chuàng)建實(shí)現(xiàn)Shape接口的抽象裝飾器類。

ShapeDecorator.java

public abstract class ShapeDecorator implements Shape {
   protected Shape decoratedShape;
   public ShapeDecorator(Shape decoratedShape){
      this.decoratedShape = decoratedShape;
   }
   public void draw(){
      decoratedShape.draw();
   }	
}

第4步

創(chuàng)建擴(kuò)展ShapeDecorator類的具體裝飾器類。

RedShapeDecorator.java

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");
   }
}

步驟 5

使用RedShapeDecorator裝飾Shape對(duì)象。

DecoratorPatternDemo.java

public class DecoratorPatternDemo {
   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();
   }
}

步驟 6

驗(yàn)證輸出。

Circle with normal border
Shape: Circle
Circle of red border
Shape: Circle
Border Color: Red
Rectangle of red border
Shape: Rectangle
Border Color: Red