Question

how to know if an object in java support clone ? or it has copy C’tor ? in run time

please provide an example ,
thank you

Answer 1

To check if supports clone check

if(myObject instanceof Cloneable) {

}

The above will tell you if the object implements Cloneable and default clone is supported or not.

But there are cases when classes dont support clone method but they provide you with some API which will create a copy of the instance, for such methods you will have to look at the API documentation or source code.

Update : Why instanceof check doesn’t guarantee a successful clone:

if(myObject instanceof Cloneable) { 
    Object obj = myObject.clone(); 
}

1-> Consider the below code snippet

public class IImplementCloneableButThrowException implements Cloneable{

    //Javadoc has a separate section for Exception, implementation like 
    //this and should clearly specify the condition in which 
    //CloneNotSupportedException will be thrown. 
    public Object clone() throws CloneNotSupportedException {
        //I implement but still wont clone, may be in future will allow myself to be cloned
        throw new CloneNotSupportedException("Sorry I cannot be cloned!");
    }
}

2-> Consider the 2nd case below

public class IImplementCloneableButCloneIsHidden implements Cloneable{
    //Ouch either no clone method or one which is Object class but that
    //has protected access modifier, which means I cannot call unless 
    //I extend it, too bad
}

So though instanceof check will pass correcltly either clone cannot be called or clone will throw exception.