| 并且实现了clone()方法。在StrClone类中声明了CloneC类型变量c1，然后调用c1的clone()方法生成c1的拷贝c2，在对c2中的String和StringBuffer类型变量用相应的方法改动之后打印结果：
package clone;
class CloneC implements Cloneable{
public String str;
public StringBuffer strBuff;
public Object clone(){
CloneC o = null;
try{
o = (CloneC)super.clone();
}catch(CloneNotSupportedException e){
e.printStackTrace();
}
return o;
}
}
public class StrClone {
public static void main(String[] a){
CloneC c1 = new CloneC();
c1.str = new String("initializeStr");
c1.strBuff = new StringBuffer("initializeStrBuff");
System.out.println("before clone,c1.str = "+ c1.str);
System.out.println("before clone,c1.strBuff = "+ c1.strBuff);
CloneC c2 = (CloneC)c1.clone();
c2.str = c2.str.substring(0,5);
c2.strBuff = c2.strBuff.append(" change strBuff clone");
System.out.println("=================================");
System.out.println("after clone,c1.str = "+ c1.str);
System.out.println("after clone,c1.strBuff = "+ c1.strBuff);
System.out.println("=================================");
System.out.println("after clone,c2.str = "+ c2.str);
System.out.println("after clone,c2.strBuff = "+ c2.strBuff);
}
}
/* RUN RESULT
before clone,c1.str = initializeStr
before clone,c1.strBuff = initializeStrBuff
=================================
after clone,c1.str = initializeStr
after clone,c1.strBuff = initializeStrBuff change strBuff clone
=================================
after clone,c2.str = initi
after clone,c2.strBuff = initializeStrBuff change strBuff clone
*
*/
打印的结果可以看出，String类型的变量好象已经实现了深度clone，因为对c2.str的改动并没有影响到c1.str！难道Java把Sring类看成了基本数据类型？其实不然，这里有一个小小的把戏，秘密就在于c2.str = c2.str.substring(0,5)这一语句！实质上，在clone的时候c1.str与c2.str仍然是引用，而且都指向了同一个String对象。但在执行c2.str = c2.str.substring(0,5)的时候，它作用相当于生成了一个新的String类型，然后又赋回给c2.str。这是因为String被Sun公司的工程师写成了一个不可更改的类（immutable class），在所有String类中的函数都不能更改自身的值。下面给出很简单的一个例子：
package clone;
public class StrTest
{
public static void main(String[] args)
{
String str1 = "This is a test for immutable";
String str2 = str1.substring(0,8);
System.out.println("print str1 : " + str1);
System.out.println("print str2 : " + str2);
}
}
/* RUN RESULT print str1 : This is a test for immutable print str2 : This is */
例子中，虽然str1调用了substring()方法，但str1的值并没有改变。类似的，String类中的其它方法也是如此。当然如果我们把最上面的例子中的这两条语句
c2.str = c2.str.substring(0,5);
c2.strBuff = c2.strBuff.append(" change strBuff clone");
改成下面这样：
c2.str.substring(0,5);
c2.strBuff.append(" change strBuff clone");
去 |
