标题：Java装饰模式

装饰器模式允许用户向现有对象添加新功能而不改变其结构。 这种类型的设计模式属于结构模式，因为此模式充当现有类的包装器。

此模式创建一个装饰器类，它包装原始类并提供附加功能，保持类方法签名完整。

我们通过以下示例展示装饰器模式的使用，其中我们将用一些颜色装饰形状而不改变形状类。

实现实例

在这个实例中，将创建一个Shape接口和实现Shape接口的具体类。然后再创建一个抽象装饰器类-ShapeDecorator，实现Shape接口并使用Shape对象作为其实例变量。

这里的RedShapeDecorator是实现ShapeDecorator的具体类。

DecoratorPatternDemo这是一个演示类，将使用RedShapeDecorator来装饰Shape对象。装饰模式示例的结构如下所示 -

第1步

创建一个简单的接口。
Shape.java

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public interface Shape {
   void draw();
}
Java

public interface Shape {
   void draw();
}
Java

第2步

创建两个实现相同接口的具体类。
Rectangle.java

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

public class Rectangle implements Shape {

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

Circle.java

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

public class Circle implements Shape {

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

第3步

创建实现Shape接口的抽象装饰器类。

ShapeDecorator.java

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

public abstract class ShapeDecorator implements Shape {
   protected Shape decoratedShape;

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

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

第4步

创建扩展ShapeDecorator类的具体装饰器类。
RedShapeDecorator.java

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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");
   }
}
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");
   }
}
Java

第5步

使用RedShapeDecorator装饰Shape对象。

DecoratorPatternDemo.java

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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();
   }
}
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();
   }
}
Java

第6步

验证输出，执行上面的代码得到以下结果 -

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

Circle with normal border
Shape: Circle

Circle of red border
Shape: Circle
Border Color: Red

Rectangle of red border
Shape: Rectangle
Border Color: Red
Java