What is wrong with this clone()?

Question

I have written this clone method for when the parent of the Employee class is abstract and the clone() method in the parent class is abstract.I wanted to copy the primitive

Answer 1

Did you implement the Cloneable interface on your object?

However, there are very few cases I would use clone for copying an object. One such safe example is array.clone(). I would rather use the copy-constructor idiom or manually copying / assigning values around.

There is Item#11 in Effective Java (2nd edition) about the background issue. Cloneable interface is a special kind of interface as it modifies the Object class' behavior regarding the cloning. Basically it is a feature enabling classinterface in Java.

Edit: Based on your example you might need to wrap the clone() call in a try-catch of CloneNotSupportedException in a general case.

Edit2: Rephrased my answer

Edit3: Did you override the clone() in the public context? In the sample you gave you try to clone an Object, which is in the java.lang package - hardly the package your code is in.

Edit4: I think the answer is already in the other posts, just wanted to reflect on the underlying issue.

Edit5: Try this:

public Object clone1() throws CloneNotSupportedException {        
    return super.clone();        
}

Edit6 Then name your method public abstract Object copy() for example and in the implementation, use the super.clone() - to avoid confusion.

Edit7 I did some eclipsing and came out with the following solution:

public class Cloner {
    public static abstract class Person {
       protected abstract Object clone1() throws CloneNotSupportedException;
       public Object copy() throws CloneNotSupportedException {
           return clone1();
       }
    }
    public static class Employee extends Person implements Cloneable {
        @Override
        protected Object clone1() throws CloneNotSupportedException {
            return super.clone();
        }
    
    }
    public static void main(String[] args) throws Exception {
        new Employee().copy();
    }
}

But basically it is the same concept as renaming your abstract method to something else than clone().

Edit8: Fixed my sample, now it works without exception.

(But the actual credit goes to Gábor Hargitai for super.clone())