Assigning values to java object

Question

I have the following code:

Color3D pixel = new Color3D(200, 0, 0);  
Color3D temporal  = pixel;  
System.out.println(util.printColor("Pixel: ", pixel));  
System.out.println(util.printColor("Temporal: ", temporal));  
pixel.setR(0);  
pixel.setG(200);  
pixel.setB(0);  
System.out.println(util.printColor("Pixel: ", pixel));  
System.out.println(util.printColor("Temporal: ", temporal));

Result:

Pixel: r: 200, g: 0, b: 0  
Temporal: r: 200, g: 0, b: 0  
Pixel: r: 0, g: 200, b: 0  
Temporal: r: 0, g: 200, b: 0

My class Color3D saves RGB (int)values.
I use the object util to print the int values of a Color3D object.

If you look at the result, for some reason after changing the red and green values of the pixel object I'm also modifying the green's values and I don't want that behaviour.

I want to have:

Pixel: r: 200, g: 0, b: 0  
Temporal: r: 200, g: 0, b: 0  
Pixel: r: 0, g: 200, b: 0  
Temporal: r: 200, g: 0, b: 0

The object temporal was created with the intention of saving the pixel object values for a future process. The object temporal will also change in future...

has your problem been solved??? plz provide me with the answer am facing a similar problem now.. — srikanth
– srikanth, Commented Jun 15, 2014 at 8:54

Matthew Flaschen · Accepted Answer · 2010-09-04 02:31:40Z

4

You're assigning references not objects.

// Create new Color3D object, and put reference in pixel reference variable
Color3D pixel = new Color3D(200, 0, 0); 
// Copy reference from pixel reference variable to temporal reference variable
Color3D temporal  = pixel;

You now have two reference variables holding equal references to the same object. Thus, any modifications are visible through both variables. You presumably want something like:

Color3D temporal  = new Color3D(pixel.getR(), pixel.getB(), pixel.getB());

I don't know if those are real methods, but you should see the idea. Note that this creates a new, independent object.

edited Sep 4, 2010 at 2:31

answered Sep 4, 2010 at 2:25

Matthew Flaschen

286k53 gold badges523 silver badges554 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Matthew Flaschen Over a year ago

@Eric, I was explaining what you did. I added another line with an idea for a solution.

kalyan Over a year ago

..which is an immutable object.

matt b · Accepted Answer · 2010-09-04 02:29:58Z

1

With this code:

Color3D pixel = new Color3D(200, 0, 0);  
Color3D temporal  = pixel;

you've only created one Color3D object. Objects are only created whenever new is called.

temporal is a reference to the same object that pixel refers to. Invoking methods on temporal is the same thing as invoking methods on pixel.

If you want each variable to refer to a different object with the same value, then you need to actually create two different objects:

Color3D pixel = new Color3D(200, 0, 0);  
Color3D temporal = new Color3D(200, 0, 0);

answered Sep 4, 2010 at 2:29

matt b

140k66 gold badges287 silver badges352 bronze badges

Comments

fastcodejava · Accepted Answer · 2010-09-04 02:35:43Z

0

Your temporal and pixel points to the same memory. So if you change one other one will pick up the change as well.

edited Sep 4, 2010 at 2:35

answered Sep 4, 2010 at 2:28

fastcodejava

41.3k31 gold badges142 silver badges191 bronze badges

Collectives™ on Stack Overflow

Assigning values to java object

3 Answers 3

2 Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

2 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related