Question

Ok this one is just bizarre – I needed two Rects for a Healthbar (border and color filling)

When I calculated the first rectangle (filling) I assigned that value to my bar rectangle – but at runtime when the filling rectangle is modified the bar is also – only by manually setting the parameters of the BarRectangle was I able to keep its shape– how is this even possible?

Can variables become linked forever through simple assignment-

Here is the entirety of the code:

  public class HealthBar {

public int MaxValue;
int CurrentValue;
public int TargetValue;

int margin = 10;
Rect Rectangle;
private  Rect BarRectangle;
int screenWidth;

boolean IsPlayer1;

 Paint paint = new Paint(); 

 int Green;
 int Yellow;
 int Red;

 int opacity = 196;

public HealthBar(boolean isPlayer1, DeviceProperties device, int maxvalue) {

    paint.setARGB(196, 0, 255, 0);
    paint.setStyle(Paint.Style.FILL);

Green = Color.argb(opacity, 0, 255, 128);
Yellow = Color.argb(opacity, 255, 255, 128);
Red = Color.argb(opacity, 255, 0, 128);


MaxValue = maxvalue;
CurrentValue = MaxValue;
TargetValue = MaxValue;


    IsPlayer1 = isPlayer1;

    screenWidth = device.Screen.width();

    if(IsPlayer1) {



        Rectangle = new Rect(
                             margin,                    //x
                             device.Screen.height() - 14, //y
                             margin + MaxValue,           //width
                             device.Screen.height() - 2  //height
                             );



    } else {



        Rectangle = new Rect(
                             device.Screen.width() - margin - MaxValue,                     //x
                             device.Screen.height() - 14, //y
                             device.Screen.width() - margin,          //width
                             device.Screen.height() - 2  //height
                             );




    }


//Assign Bar Rectangle to Rectangle
    BarRectangle = Rectangle;
}


public void Damage(int amount)
{
    TargetValue = CurrentValue - amount;
}

public void Update() 
{

    if (CurrentValue > TargetValue)
    {
        CurrentValue -= 1;

        if (IsPlayer1) 
            Rectangle.right = margin + CurrentValue;
        else
            Rectangle.left = screenWidth - margin - CurrentValue;
    }

    if (TargetValue <= MaxValue * 0.33) {
        paint.setColor(Red);
    } else if (TargetValue <= MaxValue * 0.66) {
        paint.setColor(Yellow);
    } else {
        paint.setColor(Green);
    }


}


public void Draw(ResourceManager rm, Canvas c, Paint p) 
{



    c.drawRect(Rectangle, paint);
   c.drawBitmap(rm.getBitmap("healthbar"), null, BarRectangle, p);

}


    }//End HealthBar

The way I “fixed” it was by clunkily assigning the BarRectangle seperate:

    Rectangle = new Rect(
                             margin,                    //x
                             device.Screen.height() - 14, //y
                             margin + MaxValue,           //width
                             device.Screen.height() - 2  //height
                             );


        BarRectangle = new Rect(
                 margin,                    //x
                 device.Screen.height() - 14, //y
                 margin + MaxValue,           //width
                 device.Screen.height() - 2  //height
                 );

Can anyone explain to me how assigning a variable in the COnstructor somehow makes it update it’s value whenever the other variable is updated?

Now that I’ve got a reproducable issue – I think this has happened before when it came to assigning character positions, I was using a custom class to hold the values (Vector2) and whenever one got updated the other would too.

Answer 1

The variables Rectangle and BarRectangle are reference to an object only. This means that by “simple assignment” like in your code

//Assign Bar Rectangle to Rectangle
BarRectangle = Rectangle;

you do not copy the contents (i.e. fields of your Rect) but only its reference. Changing one of the fields reflects itself in both since they now refer to the same instance.

In order to create a new instance with the same content (and therefore not share a reference) you can use the following constructor:

BarRectangle = new Rect(Rectangle);