目的
將實作體系與抽象體系分開，讓兩者能各自更動。
Decouple an abstraction from its implementation so that the two can vary independently.
適用
- 想避免將抽象和實體綁死在一起。
- 需要一個統一的介面來交換層次結構。
- 抽象體和實作體都能用子類別去個別擴充。
- 實作體有變但抽象體沒變時，不應影響client。
- 隱藏實作方式。
- 能在多個物件之間共享實作碼，但不影響client。
結構及成員
Collaborations: Abstraction將Client的訊息請求轉傳給對應的Implementor去處理。
影響結果
好處
壞處
實作
只有一種Implementor
如果實作體只會有一種，那抽象類別Implementor就不必存在（如：DBMgr），但如果希望類別內容不會影響Client，那對Bridge仍有幫助。
建立正確的Implementor物件
- 若Abstraction能認得所有的ConcreteImplementor，便可在建構子依參數決定要實體化哪一個。
- 若有大小容器，可以先預設用小的容器實作，超過臨界值再用大的容器實作。
- 也可以將決定權妥託給其他物件，如Abstract Factory。
Example
DrawAPI
public abstract class Shape {
protected DrawAPI drawAPI;
protected Shape(DrawAPI drawAPI){
this.drawAPI = drawAPI;
}
public abstract void draw();
}public class Circle extends Shape {
private int x, y, radius;
public Circle(int x, int y, int radius, DrawAPI drawAPI) {
super(drawAPI);
this.x = x;
this.y = y;
this.radius = radius;
}
public void draw() {
drawAPI.drawCircle(radius,x,y);
}
}public interface DrawAPI {
public void drawCircle(int radius, int x, int y);
}public class RedCircle implements DrawAPI {
@Override
public void drawCircle(int radius, int x, int y) {
System.out.println("Drawing Circle[ color: red, radius: " + radius + ", x: " + x + ", " + y + "]");
}
}public class GreenCircle implements DrawAPI {
@Override
public void drawCircle(int radius, int x, int y) {
System.out.println("Drawing Circle[ color: green, radius: " + radius + ", x: " + x + ", " + y + "]");
}
}public class BridgePatternDemo {
public static void main(String[] args) {
Shape redCircle = new Circle(100,100, 10, new RedCircle());
Shape greenCircle = new Circle(100,100, 10, new GreenCircle());
redCircle.draw();
greenCircle.draw();
}
}Result:
Drawing Circle[ color: red, radius: 10, x: 100, 100]
Drawing Circle[ color: green, radius: 10, x: 100, 100]Car Remote Controller
//Class: Car
package car.remotecontrol;
public abstract class Car {
private final Product product;
private final String carType;
public Car(Product product, String carType){
this.product = product;
this.carType = carType;
}
public abstract void assemble();
public abstract void produceProduct();
public void printDetails(){
System.out.println("Car: "+carType+", Product:"+product.productName());
}
}//Class: Motoren
package car.remotecontrol;
public class Motoren extends Car{
private final Product product;
private final String carType;
public Motoren(Product product, String carType) {
super(product, carType);
this.product = product;
this.carType = carType;
}
@Override
public void assemble() {
System.out.println("Assembling "+product.productName()+" for "+carType);
}
@Override
public void produceProduct() {
product.produce();
System.out.println("Modifing product "+product.productName()+" according to "+carType);
}
}//Class: BigWheel
package car.remotecontrol;
public class BigWheel extends Car{
private final Product product;
private final String carType;
public BigWheel(Product product, String carType) {
super(product, carType);
this.product = product;
this.carType = carType;
}
@Override
public void assemble() {
System.out.println("Assembling "+product.productName()+" for "+carType);
}
@Override
public void produceProduct() {
product.produce();
System.out.println("Modifing product "+product.productName()+" according to "+carType);
}
}//Interface: Product
package car.remotecontrol;
public interface Product {
public String productName();
public void produce();
}//Class: GearLocking
package car.remotecontrol;
public class GearLocking implements Product{
private final String productName;
public GearLocking(String productName){
this.productName = productName;
}
@Override
public String productName() {
return productName;
}
@Override
public void produce() {
System.out.println("Producing Gear Locking System");
}
}//Class: CentralLocking
package car.remotecontrol;
public class CentralLocking implements Product{
private final String productName;
public CentralLocking(String productName){
this.productName = productName;
}
@Override
public String productName() {
return productName;
}
@Override
public void produce() {
System.out.println("Producing Central Locking System");
}
}//Class: TestBridgePattern
package car.remotecontrol;
public class TestBridgePattern {
public static void main(String[] args) {
Product product = new CentralLocking("Central Locking System");
Product product2 = new GearLocking("Gear Locking System");
Car car = new BigWheel(product , "BigWheel xz model");
car.produceProduct();
car.assemble();
car.printDetails();
System.out.println();
car = new BigWheel(product2 , "BigWheel xz model");
car.produceProduct();
car.assemble();
car.printDetails();
System.out.println("-----------------------------------------------------");
car = new Motoren(product, "Motoren lm model");
car.produceProduct();
car.assemble();
car.printDetails();
System.out.println();
car = new Motoren(product2, "Motoren lm model");
car.produceProduct();
car.assemble();
car.printDetails();
}
}Result:
Producing Central Locking System
Modifing product Central Locking System according to BigWheel xz model
Assembling Central Locking System for BigWheel xz model
Car: BigWheel xz model, Product:Central Locking System
Producing Gear Locking System
Modifing product Gear Locking System according to BigWheel xz model
Assembling Gear Locking System for BigWheel xz model
Car: BigWheel xz model, Product:Gear Locking System
-----------------------------------------------------
Producing Central Locking System
Modifing product Central Locking System according to Motoren lm model
Assembling Central Locking System for Motoren lm model
Car: Motoren lm model, Product:Central Locking System
Producing Gear Locking System
Modifing product Gear Locking System according to Motoren lm model
Assembling Gear Locking System for Motoren lm model
Car: Motoren lm model, Product:Gear Locking System
