java 装饰模式（Decorator Pattern）详解

public interface Shape {
 void draw();
}
 

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

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

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

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");
 }
}

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();
 }
}

Circle with normal border
Shape: Circle

Circle of red border
Shape: Circle
Border Color: Red

Rectangle of red border
Shape: Rectangle
Border Color: Red