Ioc（Inversion of Control）中文翻译为“控制反转”，Ioc的抽象概念是依赖关系转移，即“程序与实现必须依赖于抽象”。
控制反转最常见的实现方式就是依赖注入（Depedency Injection），依赖注入的含义是：保留抽象接口，让组件依赖抽象接口，当组件要与其他对象发生依赖关系时，通过抽象接口来注入依赖的实际对象。
在解说Ioc之前，先看一个设计的例子：
设计一个保存数据到软盘、USB设备的程序。
设计一个保存数据到软盘、USB设备的程序。
一、反面例子，没有使用Ioc
/**
* Created by IntelliJ IDEA.
* User: leizhimin
* Date: 2007-9-25
* Time: 11:13:32
*
*
*/
public class FloppyWriter {
public void saveToDevice() {
System.out.println("FloppyWriter.saveToDevice(): Floppy!");
}
}
/**
* Created by IntelliJ IDEA.
* User: leizhimin
* Date: 2007-9-25
* Time: 11:14:25
*
*
*/
public class BusinessObject {
private FloppyWriter floppyWriter;
public FloppyWriter getFloppyWriter() {
return floppyWriter;
}
public void setFloppyWriter(FloppyWriter floppyWriter) {
this.floppyWriter = floppyWriter;
}
public void save() {
System.out.println("----BusinessObjectsave()....");
floppyWriter.saveToDevice();
System.out.println("----BusinessObjectsave()....");
}
}
/**
* Created by IntelliJ IDEA.
* User: leizhimin
* Date: 2007-9-25
* Time: 1:15:17
*
*
*/
public class Client {
public static void main(String args[]){
//
BusinessObject businessObject=new BusinessObject();
FloppyWriter floppyWriter=new FloppyWriter();
businessObject.setFloppyWriter(floppyWriter);
//
businessObject.save();
}
}
二、Ioc的实现推荐实现方式：setter方式
/**
* Created by IntelliJ IDEA.
* User: leizhimin
* Date: 2007-9-25
* Time: 11:38:32
*
*/
public interface IDeviceWriter {
public void saveToDevice();
}
/**
* Created by IntelliJ IDEA.
* User: leizhimin
* Date: 2007-9-25
* Time: 11:44:46
* ,
*/
public class FloppyWriter implements IDeviceWriter{
public void saveToDevice() {
System.out.println("FloppyWriter.saveToDevice(): Floppy!");
}
}
/**
* Created by IntelliJ IDEA.
* User: leizhimin
* Date: 2007-9-25
* Time: 11:44:57
* ,USB
*/
public class USBWriter implements IDeviceWriter{
public void saveToDevice() {
System.out.println("USBWriter.saveToDevice(): USB!");
}
}
/**
* Created by IntelliJ IDEA.
* User: leizhimin
* Date: 2007-9-25
* Time: 11:40:24
*
*/
public class BusinessObject {
private IDeviceWriter writer;
public IDeviceWriter getWriter() {
return writer;
}
public void setWriter(IDeviceWriter writer) {
this.writer = writer;
}
/**
*
*/
public void save(){
System.out.println("----BusinessObjectsave()....");
writer.saveToDevice();
System.out.println("----BusinessObjectsave()....");
}
}
/**
* Created by IntelliJ IDEA.
* User: leizhimin
* Date: 2007-9-25
* Time: 11:51:09
*
*/
public class Client {
public static void main(String args[]){
//
IDeviceWriter floppyWriter=new FloppyWriter();
IDeviceWriter usbWriter=new USBWriter();
//
BusinessObject businessObject1=new BusinessObject();
BusinessObject businessObject2=new BusinessObject();
//
businessObject1.setWriter(floppyWriter);
businessObject1.save();
System.out.println();
//
businessObject2.setWriter(usbWriter);
businessObject2.save();
}
}
三、Ioc的实现推荐实现方式：constructor方式
在setter方式基础上修改，IDeviceWriter、FloppyWriter、USBWriter不变，BusinessObject和
Client类修改为：
/**
* Created by IntelliJ IDEA.
* User: leizhimin
* Date: 2007-9-25
* Time: 11:32:03
*
*/
public class BusinessObject {
private IDeviceWriter writer;
public BusinessObject() {
}
public BusinessObject(IDeviceWriter writer) {
this.writer = writer;
}
public IDeviceWriter getWriter() {
return writer;
}
public void setWriter(IDeviceWriter writer) {
this.writer = writer;
}
/**
*
*/
public void save() {
System.out.println("----BusinessObjectsave()....");
writer.saveToDevice();
System.out.println("----BusinessObjectsave()....");
}
}
/**
* Created by IntelliJ IDEA.
* User: leizhimin
* Date: 2007-9-25
* Time: 11:35:52
*
*/
public class Client {
public static void main(String args[]){
//
IDeviceWriter floppyWriter=new FloppyWriter();
IDeviceWriter usbWriter=new USBWriter();
//
BusinessObject businessObject1=new BusinessObject(floppyWriter);
BusinessObject businessObject2=new BusinessObject(usbWriter);
//
businessObject1.save();
System.out.println();
businessObject2.save();
}
}
两种实现方式执行的结果相同：
----开始调用业务组件BusinessObject的save()方法....
调用FloppyWriter.saveToDevice()方法: 保存到了Floppy设备上!
----结束调用业务组件BusinessObject的save()方法....
调用FloppyWriter.saveToDevice()方法: 保存到了Floppy设备上!
----结束调用业务组件BusinessObject的save()方法....
----开始调用业务组件BusinessObject的save()方法....
调用USBWriter.saveToDevice()方法: 保存到了USB设备上!
----结束调用业务组件BusinessObject的save()方法....
调用USBWriter.saveToDevice()方法: 保存到了USB设备上!
----结束调用业务组件BusinessObject的save()方法....
Process finished with exit code 0
本文转自 leizhimin 51CTO博客，原文链接：http://blog.51cto.com/lavasoft/43900，如需转载请自行联系原作者