Bike 類別
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package tw.ccc99.bpandsvc;
/**
* Created by AlanJui on 2014/5/17.
*/
public class Bike {
private String manufacturer;
private String model;
private int frame;
private String serialNo;
private double weight;
private String status;
public Bike(String manufacturer, String model, int frame, String serialNo, double weight, String status) {
this.manufacturer = manufacturer;
this.model = model;
this.frame = frame;
this.serialNo = serialNo;
this.weight = weight;
this.status = status;
}
public String getManufacturer() {
return manufacturer;
}
public void setManufacturer(String manufacturer) {
this.manufacturer = manufacturer;
}
public String getModel() {
return model;
}
public void setModel(String model) {
this.model = model;
}
public int getFrame() {
return frame;
}
public void setFrame(int frame) {
this.frame = frame;
}
public String getSerialNo() {
return serialNo;
}
public void setSerialNo(String serialNo) {
this.serialNo = serialNo;
}
public double getWeight() {
return weight;
}
public void setWeight(double weight) {
this.weight = weight;
}
public String getStatus() {
return status;
}
public void setStatus(String status) {
this.status = status;
}
public String toString() {
return "Bike : " +
"manufacturer -- " + manufacturer +
"\n: model -- " + model +
"\n: frame -- " + frame +
"\n: serialNo -- " + serialNo +
"\n: weight -- " + weight +
"\n: status -- " + status +
".\n";
}
}
再開發一個：RentABike （租台腳踏車）的類別，用來管理腳踏車出租店的租借業務。在此類別先實作了 2 個方法（method），（1）getBikes：取得店裡所有的腳踏車；（2）getBike ：依「序號」取得某一台特定的腳踏車，其程式碼如下。
RentABike 類別
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package tw.ccc99.bpandsvc;
/**
* Created by AlanJui on 2014/5/17.
*/
import java.util.*;
public class RentABike {
private String storeName;
final List<Bike> bikes = new ArrayList<Bike>();
public RentABike(String storeName) {
this.storeName = storeName;
bikes.add(new Bike("Shimano", "Roadmaster", 20, "11111", 15, "Fair"));
bikes.add(new Bike("Cannondale", "F2000 XTR", 18, "22222", 12, "Excellent"));
bikes.add(new Bike("Trek", "6000", 19, "33333", 12.4, "Fair"));
}
@Override
public String toString() {
return "RentABike: " + storeName;
}
public List<Bike> getBikes() {
return bikes;
}
public Bike getBike(String serialNo) {
Iterator<Bike> iter = bikes.iterator();
while (iter.hasNext()) {
Bike bike = iter.next();
if (serialNo.equals(bike.getSerialNo())) return bike;
}
return null;
}
}
為了在螢幕上顯示店裡所有的腳踏車，我們又多開發了一個：「CommandLineView」類別，其程式碼如下。CommandLineView 類別
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package tw.ccc99.bpandsvc;
/**
* Created by AlanJui on 2014/5/17.
*/
import java.util.*;
public class CommandLineView {
private RentABike rentABike;
public CommandLineView() {
rentABike = new RentABike("Bruce's Bikes");
}
public void printAllBikes() {
System.out.println(rentABike.toString());
Iterator<Bike> iter = rentABike.getBikes().iterator();
while (iter.hasNext()) {
Bike bike = iter.next();
System.out.println(bike.toString());
}
}
public static final void main(String[] args) {
CommandLineView clv = new CommandLineView();
clv.printAllBikes();
}
}
一般的寫法，我們會很自然地在 CommandLineView 這個類別裡，先用 RentABike 類別建立一個 rentABike 物件。
以上的作法，既簡單，又直覺。但....... 它沒有達到「耦合鬆綁」所要求的程式架構之美！因 CommandLineView 類別與 RentABike 類別，十指緊扣，關係密切啊！ ^^"
那該怎麼辦咧？！
《
Spring 程式高手秘笈 》這書，在 Page 1 ~ 9 處，教人如何利用 Interface ，進行「相依注入（Dependency Injection）」，讓 CommandLineView 類別，呼叫 getBikes() 方法的這檔事 ，不是寫死在 CommandLineView 類別中，而是由另一個類別，在 Run Time 時期，負責相依關係的相注入，使 CommandLineView 物件，能呼叫 getBikes() 這方法！
這麼神奇的事，是如何做到的？
原先 RentABike 類別，能提供其它類別使用的 method ，將它當成是 service ，全包進一個名為 RentABike 的 Interface 中。
另新增一個「service 類別」 ( ArrayListRentABike ) ，須實作 (implements) 上一個 RentABike Interface 。
要使用「service 類別」，呼叫其中 method 的這種類別，稱作：「client 類別」， 以此例子而言，就是 CommandLineView 類別，它在類別中，須有一個 property ，用來指向「 service 類別」所產生的物件。
建立一個類別，負責在 Run Time 時期，執行「相依注入」的工作，這種作法，一般被稱作為 assembler 或 container 機制。在這個例子中，由 RentABikeAssembler 類別擔綱。
此相依注入的作法，可用以下的「類別圖」，來說明各個類別之間的相互關係。
最後，各類別的程式碼，分述如下。
將 RentABike 類別改成 Interface
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package tw.ccc99.bpandsvc;
/**
* Created by AlanJui on 2014/5/17.
*/
import java.util.*;
public interface RentABike {
List<Bike> getBikes();
Bike getBike(String serialNo);
}
提供 method 的「Service 類別」：ArrayListRentABike.java
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package tw.ccc99.bpandsvc;
/**
* Created by AlanJui on 2014/5/17.
*/
import java.util.*;
public class ArrayListRentABike implements RentABike {
private String storeName;
final List<Bike> bikes = new ArrayList<Bike>();
public ArrayListRentABike() {
initBikes();
}
public ArrayListRentABike(String storeName) {
this.storeName = storeName;
initBikes();
}
public void initBikes() {
bikes.add(new Bike("Shimano", "Roadmaster", 20, "11111", 15, "Fair"));
bikes.add(new Bike("Cannondale", "F2000 XTR", 18, "22222", 12, "Excellent"));
bikes.add(new Bike("Trek", "6000", 19, "33333", 12.4, "Fair"));
}
@Override
public String toString() {
return "RentABike: " + storeName;
}
public List<Bike> getBikes() {
return bikes;
}
public Bike getBike(String serialNo) {
Iterator<Bike> iter = bikes.iterator();
while (iter.hasNext()) {
Bike bike = iter.next();
if (serialNo.equals(bike.getSerialNo())) return bike;
}
return null;
}
}
使用 method 的「Client 類別」：CommandLineView.java
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package tw.ccc99.bpandsvc;
/**
* Created by AlanJui on 2014/5/17.
*/
import java.util.*;
public class CommandLineView {
private RentABike rentABike;
public CommandLineView() {}
public void setRentABike(RentABike rentABike) {
this.rentABike = rentABike;
}
public RentABike getRentABike() {
return rentABike;
}
public void printAllBikes() {
for (Bike bike: rentABike.getBikes()) {
System.out.println(bike.toString());
}
}
}
注入相依的 Assembler 類別：RentABikeAssembler.java
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package tw.ccc99.bpandsvc;
/**
* Created by AlanJui on 2014/5/17.
*/
public class RentABikeAssembler {
public static final void main(String[] args) {
CommandLineView clv = new CommandLineView();
RentABike rentABike = new ArrayListRentABike("Bruce's Bikes");
clv.setRentABike(rentABike);
clv.printAllBikes();
}
}
Run Time 時期，由 RentABikeAssembler 類別，負責「注入相依關係」這檔事。
首先，建立一個「Client 物件」： CommandLineView 物件；然後，建立一個「Service 物件」： ArrayListRentABike。
接著令「Client 物件」－ CommandLineView 的 property 指向「Service 件件」 － ArrayListRentABike。 最後， CommandLineView 這個「Client 物件」，可以使用 「Service 物件」－ ArrayListRentABike ， 提供的 getBikes() 方法，取出店裡所有的腳踏車，丟給類別內的方法處理，顯示在螢幕上 。
