Clone() in java

Question

import java.util.*;
import java.lang.*;

public class Test{
    public static void main(String[] argv){
        String s1="abc";
        String s2=(String) s1.clone();
    }    
}

Why this simple test program doesn't work?

Answer 1

clone is a method of the Object class. For a class to be "cloneable" it should implement the marker Cloneable interface. String class doesn't implement this interface and doesn't override the clone method hence the error.

I hope the above snippet is for educational purposes because you should never feel a need to call clone on strings in Java given that:

1. Strings in Java are immutable. Feel free to share them across methods/classes
2. There already exists a constructor new String(String) which acts like a copy constructor and is pretty much equivalent to your clone() call.

Answer 2

Object.clone() is protected. It is a tricky API to use.

Usually one exposes clone() when one extends Object by broadening the method's visibility.

Clone on any string has little meaning, since it is both final and immutable.

There is a reason to copy a string; that can be done with:

String s1 = ...;
String s2 = new String(s1)