Question

The Java documentation says:

A class implements the Cloneable
interface to indicate to the
Object.clone() method that it is
legal for that method to make a
field-for-field copy of instances of
that class.

Invoking Object’s clone method on an
instance that does not implement the
Cloneable interface results in the
exception CloneNotSupportedException
being thrown.

By convention, classes that implement
this interface should override
Object.clone (which is protected) with
a public method. See Object.clone()
for details on overriding this method.

Note that this interface does not
contain the clone method. Therefore,
it is not possible to clone an object
merely by virtue of the fact that it
implements this interface. Even if the
clone method is invoked reflectively,
there is no guarantee that it will
succeed.

And I have this UserProfile class:

public class UserProfile implements Cloneable {
    private String name;
    private int ssn;
    private String address;

    public UserProfile(String name, int ssn, String address) {
        this.name = name;
        this.ssn = ssn;
        this.address = address;
    }

    public UserProfile(UserProfile user) {
        this.name = user.getName();
        this.ssn = user.getSSN();
        this.address = user.getAddress();
    }

    // get methods here...

    @Override
    public UserProfile clone() {
        return new UserProfile(this);
    }
}

And for testing porpuses, I do this in main():

UserProfile up1 = new UserProfile("User", 123, "Street");
UserProfile up2 = up1.clone();

So far, no problems compiling/running. Now, per my understanding of the documentation, removing implements Cloneable from the UserProfile class should throw an exception in up1.clone() call, but it doesn’t.

I’ve read around here that the Cloneable interface is broken but I don’t really know what that means. Am I missing something?

Answer 1

Now, per my understanding of the documentation, removing implements Cloneable from the UserProfile class should throw and exception in up1.clone() call, but it doesn’t.

As long as your class still has an implementation of the clone() method, an exception will ofcourse not be thrown when you call it – it works just like any other method, there’s no special magic involved.

The implementation of clone() in class Object is what throws the exception, but you’ve overridden that method.