前言:为了解决子类膨胀问题,把被装饰的以关联的方式放入装饰类里面,装饰类添加新的功能,如果需要再扩展新功能的时候,那么可以考虑直接继承装饰类。下面是一个画圆的例子(其实ServletRequest、HttpServletRequest、ServletRequestWrapper以及HttpServletRequestWrapper就是用的装饰器模式)
JAVA语言版装饰器模式
创建接口:
public interface Shape {
void draw();
}
接口的实现类:
public class Rectangle implements Shape{
@Override
public void draw() {
System.out.println("形状:矩形");
}
}
public class Circle implements Shape{
@Override
public void draw() {
System.out.println("形状:圆形");
}
}
创建一个装饰器类的抽象类:
public abstract class ShapeDecorator implements Shape {
protected Shape decoratorShape;
public ShapeDecorator(Shape decoratorShape) {
this.decoratorShape = decoratorShape;
}
@Override
public void draw() {
decoratorShape.draw();
}
}
创建继承抽象类的非抽象类:
public class RedShapeDecorator extends ShapeDecorator {
public RedShapeDecorator(Shape decoratorShape) {
super(decoratorShape);
}
public void draw() {
decoratorShape.draw();
serRedBorder();
}
private void serRedBorder() {
System.out.println("线的颜色:红色");
}
}
创建DecoratorpatternDemo类用来演示装饰器模式:
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("没有包装的圆:");
circle.draw();
System.out.println("包装后的红色圆:");
redCircle.draw();
System.out.println("包装后的矩形:");
redRectangle.draw();
}
}
输出结果:
没有包装的圆:
形状:圆形
包装后的红色圆:
形状:圆形
线的颜色:红色
包装后的矩形:
形状:矩形
线的颜色:红色