简谈设计模式之桥接模式

桥接模式是一种结构型设计模式, 它将抽象部分和它的实现部分分离, 使它们可以独立变化. 这意味着可以改变它的抽象和它的实现, 而不会相互影响

桥接模式结构

抽象 (Abstraction): 定义抽象类, 并包含一个对实现类对象的引用
拓展抽象 (Refined Abstraction): 拓展抽象类, 通过组合的方式调用实现类的方法
实现 (Implementor): 定义实现类的接口, 但不具体实现, 它仅提供一个接口, 供具体实现类进行实现
具体实现 (ConcreteImplementor): 具体实现Implementor接口

桥接模式实现

假设有一个画图程序, 需要渲染不同图形, 同时还需要在不同操作系统上渲染, 可以使用桥接模式来实现这个程序

// Implementor
interface DrawingAPI {void drawCircle(double x, double y, double radius);
}// ConcreteImplementorA
class DrawingAPI1 implements DrawingAPI {@Overridepublic void drawCircle(double x, double y, double radius) {System.out.println("API1.circle at " + x + ":" + y + " radius " + radius);}
}// ConcreteImplementorB
class DrawingAPI2 implements DrawingAPI {@Overridepublic void drawCircle(double x, double y, double radius) {System.out.println("API2.circle at " + x + ":" + y + " radius " + radius);}
}// Abstraction
abstract class Shape {protected DrawingAPI drawingAPI;protected Shape(DrawingAPI drawingAPI) {this.drawingAPI = drawingAPI;}public abstract void draw();                               // low-levelpublic abstract void resizeByPercentage(double pct);       // high-level
}// RefinedAbstraction
class CircleShape extends Shape {private double x, y, radius;public CircleShape(double x, double y, double radius, DrawingAPI drawingAPI) {super(drawingAPI);this.x = x;this.y = y;this.radius = radius;}@Overridepublic void draw() {drawingAPI.drawCircle(x, y, radius);}@Overridepublic void resizeByPercentage(double pct) {radius *= (1.0 + pct / 100.0);}
}// Client
public class BridgePatternDemo {public static void main(String[] args) {Shape[] shapes = new Shape[] {new CircleShape(1, 2, 3, new DrawingAPI1()),new CircleShape(5, 7, 11, new DrawingAPI2()),};for (Shape shape : shapes) {shape.resizeByPercentage(2.5);shape.draw();}}
}