How do I build a copy constructor that receive another point (x,y) and copy its values ?
I decide a signature: public Point1 (Point1 other)
, but I don't know what to write in it...
The Point class looks like:
public class Point1
{
private int _x , _y;
public Point1 (Point1 other)
{
...
...
}
//other more constructors here...
}
I tried:
public Point1 (Point1 other)
{
_x = other._x ;
_y = other._y;
}
But I almost sure I can do it better..
thnx
Nope, your attempt of
public Point1(Point1 other)
{
_x = other._x ;
_y = other._y;
}
is absolutely fine... (I've corrected the parameter type.)
I'd be tempted to make _x
and _y
final, and make the class final, but that's because I like immutable types. Others definitely have different opinions :)
Cloning on an inheritance hierarchy is slightly trickier - each class in the hierarchy has to have a relevant constructor, pass whatever argument it's given to the superclass constructor, and then copy just its own fields. For example:
public class Point2 extends Point1
{
private int _z;
public Point2(Point2 other)
{
super(other);
this._z = other._z;
}
}
That's not too bad on the implementation side, but if you want to faithfully clone a Point2
you need to know it's a Point2
in order to call the right constructor.
Implementing Cloneable
allows this to be done a bit more simply, but there are other things to consider around that... basically cloning objects isn't as simple as it might appear :) (I'm sure there's an entry in Effective Java for it. If you don't have a copy, buy one now.)
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