Question

I have a class (Literal). I need to be able to keep an intact Literal instance in memory throughout my application, and have a copy of it which I can alter. I have used two ways to do this:

1. class Literal implements Cloneable and override Object.clone() method.

2. Factory constructor:

   public Literal(Literal lit){
        this = lit;
   }
   

In both cases copying doesn’t work. Every change I make to the copy, changes the original. Does anybody have any idea what I’m doing wrong?

Answer 1

If you are going to use copy-constructor, then you will need to make a deep copy of every mutable member variable.

Say your Literal has member variables like this:

private String[] args;
private String s;

Then your copy-constructor would need to do something like this

public Literal(Literal l) {
  // have to deep copy the array, otherwise both instances are sharing the reference
  this.args = Arrays.copyOf(l.args, l.args.length);

  // safe to just copy the reference, String is immutable
  this.s = l.s;
}