设计模式（结构型）之桥梁模式
GOF 在《设计模式》中给桥梁模式的定义为：将抽象部分与它的实现部分分离，使它们都可以独立地变化。这里的抽象部分和实现部分不是我们通常认为的父类与子类、接口与实现类的关系，而是组合关系。也就是说，实现部分是被抽象部分调用，以用来完成（实现）抽象部分的功能。
桥梁模式的用意是"将抽象化（Abstraction）和实现化（Implementation）脱耦，使得二者可以独立地变化。"
抽象化：
存在于多个实体中的共同的概念性联系，就是抽象化。
实现化：
抽象化给出的具体实现，就是实现化。
脱耦：
耦合，就是两个实体的行为的某种强关联。脱耦，就是将这种强关联去掉。
强关联，就是在编译时期就确定了，无法在运行时期动态改变的关联。
弱关联，就是可以动态地确定，并可以在运行时期动态地改变的关联。
Java中，继承关系是强关联，组合（聚合）关系是软关联。
一、组成：
1) 抽 象 （ Abstraction ） 角色： 它定义了抽象类的接口而且维护着一个指向实现角色的引用。
2) 精确\修正抽象（RefinedAbstraction\SpecializedAbstraction）角色：实现并扩充由抽象角色定义的接口。
3) 实现（Implementor）角色：给出了实现类的接口，这里的接口与抽象角色中的接口可以不一致。实现化角色应当只给出底层操作，而抽象化角色应当只给出基于底层操作的更高一层的操作。
4) 具体实现（ConcreteImplementor）角色：给出了实现角色定义接口的具体实现。
二、UML类图：
三、类图的代码描述（JAVA）：
以下代码来自《Thinking in Patterns with Java》：
//抽象部分的抽象角色
class Abstraction {
//维护着一个指向实现（Implementor）角色的引用
private Implementation implementation;
public Abstraction(Implementation imp) {
implementation = imp;
}
// 下面定义了抽象部分应该有的接口
public void service1() {
//使用了实现部分已有的接口
//组合实现功能
implementation.facility1();
implementation.facility2();
}
public void service2() {
implementation.facility2();
implementation.facility3();
}
public void service3() {
implementation.facility1();
implementation.facility2();
implementation.facility4();
}
// For use by subclasses:
protected Implementation getImplementation() {
return implementation;
}
}
//抽象部分的精确抽象角色
class ClientService1 extends Abstraction {
public ClientService1(Implementation imp) {
super(imp);
}
//使用抽象角色提供的方法组合起来完成某项功能
//这就是为什么叫精确抽象角色（修正抽象角色）
public void serviceA() {
service1();
service2();
}
public void serviceB() {
service3();
}
}
//另一个精确抽象角色，和上面一样的被我省略了
class ClientService2 extends Abstraction {
//这里是直接通过实现部分的方法来实现一定的功能
public void serviceE() {
getImplementation().facility3();
}
}
//实现部分的实现角色
interface Implementation {
//这个接口只是定义了一定的接口
void facility1();
void facility2();
void facility3();
void facility4();
}
//具体实现角色就是要将实现角色提供的接口实现
//并完成一定的功能
//这里省略了
class Implementation1 implements Implementation {
......
}
class Implementation2 implements Implementation {
......
}
......
在上面的程序中还体现出一点特色：就是不仅实现部分和抽象部分所提供的接口可以完全不一样；而且实现部分内部、抽象部分内部的接口也完全可以不一样。但是实现部分要提供类似的功能才行。
四、详细代码实现：
在这里，我用了一个具体的例子：
现在我要画画，要画矩形（Rectangle）和三角形（Triangle）两种形状的形状（Shape），但是我又要画实线（SolidLine）和虚线（DotLine）两种线条（Line）。
这样，我们就可以把形状看成抽象化，把线条看成实现化；矩形和三角形就是修正抽象化，实线和虚线就是具体实现化。
JAVA：
Shape.java:
// 抽象化角色
package abstraction;
import implementation.Line;
public class Shape {
protected Line line;
protected int x1;
protected int y1;
protected int x2;
protected int y2;
public Shape(){}
public Shape(Line line,int x1, int y1, int x2, int y2){
this.line = line;
this.x1 = x1;
this.y1 = y1;
this.x2 = x2;
this.y2 = y2;
}
public void show(){
}
public int calculateArea(){
return 0;
}
public int calculatePerimeter(){
return 0;
}
}
Rectangle.java:
// 修正抽象化角色
package abstraction;
import implementation.Line;
public class Rectangle extends Shape {
public Rectangle(Line line,int x1, int y1, int x2, int y2){
super(line, x1, y1, x2, y2);
}
public void show(){
System.out.println("This is an Rectangle!");
line.draw(x1, y1, x2, y2);
}
public int calculateArea(){
return Math.abs((x2 - x1)*(y2 - y1));
}
public int calculatePerimeter(){
return 2*(Math.abs(x2 - x1) + Math.abs(y2 - y1));
}
}
Triangle.java:
// 修正抽象化角色
package abstraction;
import implementation.Line;
public class Triangle extends Shape {
public Triangle(Line line,int x1, int y1, int x2, int y2){
super(line, x1, y1, x2, y2);
}
public void show(){
System.out.println("This is an Triangle!");
line.draw(x1, y1, x2, y2);
}
public int calculateArea(){
return Math.abs((x2 - x1)*(y2 - y1))/2;
}
public int calculatePerimeter(){
int a = Math.abs(x2 - x1);
int b = Math.abs(y2 - y1);
int c = (int)Math.sqrt(a*a + b*b);
return a + b + c;
}
}
Line.java:
// 实现化角色
package implementation;
public class Line {
protected int x1;
protected int y1;
protected int x2;
protected int y2;
public void draw(int x1, int y1, int x2, int y2){
}
}
DotLine.java:
// 具体实现化角色
package implementation;
public class DotLine extends Line {
protected int x1;
protected int y1;
protected int x2;
protected int y2;
public void draw(int x1, int y1, int x2, int y2){
System.out.println("drawSolidLine:"+x1+","+y1+","+x2+","+y2);
}
}
SolidLine.java:
// 具体实现化角色
package implementation;
public class SolidLine extends Line {
protected int x1;
protected int y1;
protected int x2;
protected int y2;
public void draw(int x1, int y1, int x2, int y2){
System.out.println("drawDotLine:"+x1+","+y1+","+x2+","+y2);
}
}
mainDraw.java:
// 实现
import abstraction.*;
import implementation.*;
public class mainDraw {
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
int x1=0, y1=0, x2=1, y2=1;
Line solidLine = new SolidLine();
Line dotLine = new DotLine();
Shape solidLineRectangle = new Rectangle(solidLine,x1, y1, x2, y2);
Shape dotLineRectangle = new Rectangle(dotLine,x1, y1, x2, y2);
Shape solidLineTriangle = new Triangle(solidLine,x1, y1, x2, y2);
Shape dotLineTriangle = new Triangle(dotLine,x1, y1, x2, y2);
System.out.println("########################");
System.out.println("solidLineRectangle:");
solidLineRectangle.show();
System.out.println("area:"+solidLineRectangle.calculateArea());
System.out.println("perimeter:"+solidLineRectangle.calculatePerimeter());
System.out.println("########################");
System.out.println("dotLineRectangle:");
dotLineRectangle.show();
System.out.println("area:"+dotLineRectangle.calculateArea());
System.out.println("perimeter:"+dotLineRectangle.calculatePerimeter());
System.out.println("########################");
System.out.println("solidLineTriangle:");
solidLineTriangle.show();
System.out.println("area:"+solidLineTriangle.calculateArea());
System.out.println("perimeter:"+solidLineTriangle.calculatePerimeter());
System.out.println("########################");
System.out.println("dotLineTriangle:");
dotLineTriangle.show();
System.out.println("area:"+dotLineTriangle.calculateArea());
System.out.println("perimeter:"+dotLineTriangle.calculatePerimeter());
}
}
输出结果：
########################
solidLineRectangle:
This is an Rectangle!
drawDotLine:0,0,1,1
area:1
perimeter:4
########################
dotLineRectangle:
This is an Rectangle!
drawSolidLine:0,0,1,1
area:1
perimeter:4
########################
solidLineTriangle:
This is an Triangle!
drawDotLine:0,0,1,1
area:0
perimeter:3
########################
dotLineTriangle:
This is an Triangle!
drawSolidLine:0,0,1,1
area:0
perimeter:3
C++：
shape.h（定义在include包中）:
// 抽象化角色
#ifndef SHAPE_H_
#define SHAPE_H_
#include "lines.h"
#include
using namespace std;
class Shape{
public:
Shape(){}
Shape(Line &line,int x1, int y1, int x2, int y2){
this->line = &line;
this->x1 = x1;
this->y1 = y1;
this->x2 = x2;
this->y2 = y2;
}
virtual void show() = 0;
virtual int calculateArea() = 0;
virtual int calculatePerimeter() = 0;
virtual ~Shape(){}
protected:
Line* line;
int x1, y1, x2, y2;
};
class Rectangle : public Shape{
public:
Rectangle(Line &line,int x1, int y1, int x2, int y2);
int calculateArea();
int calculatePerimeter();
void show();
virtual ~Rectangle(){}
protected:
int x1, y1, x2, y2;
};
class Triangle : public Shape {
public:
Triangle(Line &line,int x1, int y1, int x2, int y2);
void show();
int calculateArea();
int calculatePerimeter();
private:
int x1, y1, x2, y2;
};
#endif
line.h（定义在include包中）:
// 实现化角色
#ifndef LINES_H_
#define LINES_H_
class Line{
public:
virtual void draw(int x1, int y1, int x2, int y2) = 0;
virtual ~Line(){};
};
class SolidLine:public Line{
public:
void draw(int x1, int y1, int x2, int y2);
virtual ~SolidLine(){};
};
class DotLine:public Line{
public:
void draw(int x1, int y1, int x2, int y2);
virtual ~DotLine(){};
};
#endif /* LINES_H_ */
Rectangle.cpp:
// 修正实现角色
#include "../include/shape.h"
#include
Rectangle::Rectangle(Line &line,int x1, int y1, int x2, int y2){
this->line = &line;
this->x1 = x1;
this->y1 = y1;
this->x2 = x2;
this->y2 = y2;
}
int Rectangle::calculateArea(){
return abs((x2 - x1)*(y2 - y1));
}
int Rectangle::calculatePerimeter(){
return 2*(abs(x2 - x1) + abs(y2 - y1));
}
void Rectangle::show(){
cout << "Rectangle" << endl;
line->draw(x1, y1, x1, y2);
}
Triangle.cpp:
// 修正实现角色
#include "../include/shape.h"
#include
#include
Triangle::Triangle(Line &line, int x1, int y1, int x2, int y2){
this->line = &line;
this->x1 = x1;
this->y1 = y1;
this->x2 = x2;
this->y2 = y2;
}
int Triangle::calculateArea(){
return abs((x2 - x1)*(y2 - y1))/2;
}
int Triangle::calculatePerimeter(){
int a = abs(x2 - x1);
int b = abs(y2 - y1);
int c = (int)sqrt(a*a + b*b);
return a + b + c;
}
void Triangle::show(){
cout << "Triangle" << endl;
line->draw(x1, y1, x1, y2);
}
DotLine.cpp:
// 具体实现化角色
#include "../include/lines.h"
#include
#include
using namespace std;
void DotLine::draw(int x1, int y1, int x2, int y2){
cout << "drawDotLine" << x1 << "," << y1 << "," << x2 << "," << y2 << endl;
}
SolidLine.cpp:
// 具体实现化角色
#include "../include/lines.h"
#include
#include
using namespace std;
void SolidLine::draw(int x1, int y1, int x2, int y2){
cout << "drawSolidLine" << x1 << "," << y1 << "," << x2 << "," << y2 << endl;
}
Bridge.cpp
// 实现
//============================================================================
// Name : Bridge.cpp
// Author : Yan Chao
// Version :
// Copyright : Your copyright notice
// Description : Hello World in C++, Ansi-style
//============================================================================
#include "../include/shape.h"
#include "../include/lines.h"
int main() {
int x1=0, y1=0, x2=1, y2=1;
Line *solidLine = new SolidLine();
Line *dotLine = new DotLine();
Shape *solidLineRectangle = new Rectangle(*solidLine,x1, y1, x2, y2);
Shape *dotLineRectangle = new Rectangle(*dotLine,x1, y1, x2, y2);
Shape *solidLineTriangle = new Triangle(*solidLine,x1, y1, x2, y2);
Shape *dotLineTriangle = new Triangle(*dotLine,x1, y1, x2, y2);
cout << "solidLineRectangle:" << endl;
solidLineRectangle->show();
cout << "dotLineRectangle:" << endl;
dotLineRectangle->show();
cout << "solidLineTriangle:" << endl;
solidLineTriangle->show();
cout << "dotLineTriangle:" << endl;
dotLineTriangle->show();
return 0;
}
输出结果：
solidLineRectangle:
Rectangle
drawSolidLine0,0,0,1
dotLineRectangle:
Rectangle
drawDotLine0,0,0,1
solidLineTriangle:
Triangle
drawSolidLine0,0,0,1
dotLineTriangle:
Triangle
drawDotLine0,0,0,1
