Java克隆Clone
☆什麼是Clone Clone就是得到一個物件x的副本，而且x.clone() != x。Clone分為兩種：淺度克隆Shallow Clone和淺度克隆Deep Clone


Object類有clone()方法： protected native Object clone() throws CloneNotSupportedException; 但是Object本身沒有implements Cloneable，在執行clone方法時，先檢查this.getClass()是否實現了cloneable介面，如果沒有實現Cloneable介面，clone()就會拋CloneNotSupportedException返回。否則就會建立一個新的this.getClass()的物件other，並將this每一個field的值賦值給other的對應field，然後返回other。

介面Cloneable起一個標誌作用(和Serializable類似)，用來標誌該類具有克隆功能。


☆實現Shallow clone Shallow Clone只是將基本型別賦值過去，對於物件傳的是引用。(String對於比較特別，[一般內容一樣則引用一樣，輕量級模式])Shallow Clone
public class Test {
public static void main(String[] args) throws Exception{
Area area=new Area("fujian");
System.out.println("area:"+area);
Area areaClone=area.clone();
System.out.println("areaClone:"+areaClone);
System.out.println("area==areaClone:"+(area==areaClone));
System.out.println("area.getClass()==areaClone.getClass():"+(area.getClass()==areaClone.getClass()));
area.province="jiangxi";
System.out.println("area:"+area);
System.out.println("areaClone:"+areaClone);
}
}

class Area implements Cloneable{
String province;
Area(String province){
this.province=province;
}

@Override
public Area clone(){
Area area=null;
try{
area=(Area)super.clone();
}catch(CloneNotSupportedException cnse){
cnse.printStackTrace();
}
return area;
}

@Override
public String toString(){
return "\tprovince="+province;
}
}輸出結果
area: province=fujian
areaClone: province=fujian
area==areaClone:false
area.getClass()==areaClone.getClass():true
area: province=jiangxi
areaClone: province=fujian

☆Shallow Clone的問題 因為對於物件只是拷貝引用，所有就會造成this對其中物件的修改引起other中相應物件的修改，例子如下：Shallow Clone問題
public class Test {
public static void main(String[] args) throws Exception{
Area area=new Area("fujian","fujian info");
Area areaClone=area.clone();
System.out.println("area:"+area);
System.out.println("areaClone:"+areaClone);
area.province="jiangxi";
area.info.name="new info";
System.out.println("--------After Change-------");
System.out.println("area:"+area);
System.out.println("areaClone:"+areaClone);
}
}

class Area implements Cloneable{
String province;
Info info;
Area(String province,String infoName){
this.province=province;
info=new Info(infoName);
}

@Override
public Area clone(){
Area area=null;
try{
area=(Area)super.clone();
}catch(CloneNotSupportedException cnse){
cnse.printStackTrace();
}
return area;
}

@Override
public String toString(){
return "\tprovince="+province+"\t info="+info.name;
}
}

class Info{
String name;
Info(String name){
this.name=name;
}
}輸出結果
area: province=fujian info=fujian info
areaClone: province=fujian info=fujian info
--------After Change-------
area: province=jiangxi info=new info
areaClone: province=fujian info=new info


☆Deep Clone 有些時候我們不希望this與other之間的修改相互影響，這時就應該用深度克隆。對所有涉及到的物件也實現Clone。Deep Clone
public class Test {
public static void main(String[] args) throws Exception{
Area area=new Area("fujian","fujian info");
Area areaClone=area.clone();
System.out.println("area:"+area);
System.out.println("areaClone:"+areaClone);
area.province="jiangxi";
area.info.name="new info";
System.out.println("--------After Change-------");
System.out.println("area:"+area);
System.out.println("areaClone:"+areaClone);
}
}

class Area implements Cloneable{
String province;
Info info;
Area(String province,String infoName){
this.province=province;
info=new Info(infoName);
}

@Override
public Area clone(){
Area area=null;
try{
area=(Area)super.clone();
area.info=this.info.clone();
}catch(CloneNotSupportedException cnse){
cnse.printStackTrace();
}
return area;
}

@Override
public String toString(){
return "\tprovince="+province+"\t info="+info.name;
}
}

class Info implements Cloneable{
String name;
Info(String name){
this.name=name;
}
@Override
public Info clone(){
Info info=null;
try{
info=(Info)super.clone();
}catch(CloneNotSupportedException cnse){
cnse.printStackTrace();
}
return info;
}
}輸出結果
area: province=fujian info=fujian info
areaClone: province=fujian info=fujian info
--------After Change-------
area: province=jiangxi info=new info
areaClone: province=fujian info=fujian info

☆參考：
http://www.blogjava.net/orangelizq/archive/2007/10/17/153573.html
http://www.blogjava.net/junky/archive/2007/05/08/115928.html