clone与重新new一个的区别在哪里
下面这个程序我有两个问题,它只得出第一次输出,第二次输出没有出现,有错误提示,不知错在哪里?另外我想问clone与重新new一个的区别。
import java.util.*;
public class Test2
{
public static void main(String[] args)
{
A a = new A("abc");
A b = a;
b.name = "opq";
System.out.println(a.name);//输出的结果是"opq",
//改变了a.name的值。
//clone应该不会改变a.name的值,所以下面的结果应该是"opq",
//但是由于程序有误,没有得到结果,请指正。
try
{
A c = a.clone();
c.name = "rst";
System.out.println(a.name);
}
catch(CloneNotSupportedException e)
{
e.printStackTrace();
}
}
}
class A
{
public String name;
{
name = n;
}
public A clone() throws CloneNotSupportedException
{
A cloned = (A)super.clone();
public A(String n)
return cloned;
}
}
给出的错误提示是
------解决方案--------------------学会自己看API,说的很详细:
protected Object clone()
throws CloneNotSupportedException
Creates and returns a copy of this object. The precise meaning of "copy" may depend on the class of the object. The general intent is that, for any object x, the expression:
x.clone() != x
will be true, and that the expression:
x.clone().getClass() == x.getClass()
will be true, but these are not absolute requirements. While it is typically the case that:
x.clone().equals(x)
will be true, this is not an absolute requirement.
By convention, the returned object should be obtained by calling super.clone. If a class and all of its superclasses (except Object) obey this convention, it will be the case that x.clone().getClass() == x.getClass().
By convention, the object returned by this method should be independent of this object (which is being cloned). To achieve this independence, it may be necessary to modify one or more fields of the object returned by super.clone before returning it. Typically, this means copying any mutable objects that comprise the internal "deep structure" of the object being cloned and replacing the references to these objects with references to the copies. If a class contains only primitive fields or references to immutable objects, then it is usually the case that no fields in the object returned by super.clone need to be modified.
The method clone for class Object performs a specific cloning operation. First, if the class of this object does not implement the interface Cloneable, then a CloneNotSupportedException is thrown. Note that all arrays are considered to implement the interface Cloneable and that the return type of the clone method of an array type T[] is T[] where T is any reference or primitive type. Otherwise, this method creates a new instance of the class of this object and initializes all its fields with exactly the contents of the corresponding fields of this object, as if by assignment; the contents of the fields are not themselves cloned. Thus, this method performs a "shallow copy" of this object, not a "deep copy" operation.