Java inheritance: "Casting" variable in abstract class as static

Question

I'm seeking to reduce redundant code in my Android project. Let me tell you what I already have.

I have two main groups of views. One is called MapView, which is a View containing a bitmap that can be zoomed, panned, etc. The other is called StepInfoView, which is a View that contains static data, such as an array of coordinates and information about those coordinates. This View is also zoomed and panned in an identical way as the MapView is, however, the scale factors and amount panned needs to be independent from the MapView.

StepInfoView is extended by several different classes (6 in total), all of which need to be in sync (coordinates are plotted on one, lines between coordinates are plotted on another, etc.).

So, here is the gist of my code, currently:

public class MapView extends View
{
    protected float scale = 1;

    protected class ScaleListener extends ScaleGestureDetector.SimpleOnScaleGestureListener
    {
        @Override
        public boolean onScale(ScaleGestureDetector detector)
        {
            scale *= detector.getScaleFactor());
            return true;
        }

    }

    }
... 

public class StepInfoView extends View
{
    static protected float scale = 1;
    protected class ScaleListener extends ScaleGestureDetector.SimpleOnScaleGestureListener
    {
        @Override
        public boolean onScale(ScaleGestureDetector detector)
        {
            scale *= detector.getScaleFactor());
            return true;
        }

    }
}
...
public class StepView extends StepInfoView
{  
    // Custom onDraw, same scale as PathView
}
public class PathView extends StepInfoView
{
    // Custom onDraw, same scale as StepView
}

As you see, the onScales are identical. I want to create an abstract class to hold the scaling function, let us call it RootView. Both the MapView and StepInfoView have scales, but I cannot make scale static in RootView because the MapView scale must be independent of the StepInfoView. Here is a solution that I know would work, but I don't like the clutter of getters and setters:

abstract class RootView extends View
{
    abstract protected float getScale();

    abstract protected void setScale(float s);
    protected class ScaleListener extends ScaleGestureDetector.SimpleOnScaleGestureListener
    {
        @Override
        public boolean onScale(ScaleGestureDetector detector)
        {
         setScale(getScale() * detector.getScaleFactor());
         return true;
        }
    }
}
...
public class MapView extends RootView
{
    public float scale = 1;
    protected float getScale(){
        return scale;
    }

    protected void setScale(float s){
        scale = s;
    }
}

public class StepInfoView extends RootView
{
    public static float scale = 1;
    protected float getScale(){
        return scale;
    }

    protected void setScale(float s){
        scale = s;
    }
}
public class StepView extends StepInfoView
{  
    // Custom onDraw, same scale as PathView
}
public class PathView extends StepInfoView
{
    // Custom onDraw, same scale as StepView
}

That works exactly how I want it to work, but once again, there is duplicated identical code (getters and setters and a "scale" variable in MapView and StepInfoView).

What I wish I could do is declare a non-static scale in RootView and "cast" it as static in StepInfoView. That's not exactly possible...

Can ya help me out?

Peter Lawrey · Accepted Answer · 2012-08-03 11:45:41Z

1

A float costs about 4 bytes. Having another classes will use quite a bit more memory than this. As objects are typically 8 byte aligned, it may not even make the object smaller.

If you want to avoid complexity I would leave the field as non-static.

You could have

class RootView {
    protected final float[] scale;

    RootView() {
        scale = new float[] { 1.0f };
    }

    protected RootView(float[] scale) {
        this.scale = scale;
    }

    public boolean onScale(ScaleGestureDetector detector) {
        scale[0] *= detector.getScaleFactor();
        return true;
    }
}

class StepInfoView extends RootView {
    static final float[] scale = { 1.0f };

    StepInfoView() {
        super(scale);
    }

edited Aug 3, 2012 at 11:45

answered Aug 3, 2012 at 11:35

Peter Lawrey

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6 Comments

androidnotgenius Over a year ago

I'm not concerned with memory for this application. Leaving the field as non-static would require me to update all of the classes that extend StepBaseInfo individually if scale changes.

androidnotgenius Over a year ago

So, this works great with just scale, but I also have a variable "position", the amount panned for MapView and the StepInfoViews, that is handled in the same manner as scale (non-static for Map, static for StepInfo). Can I do super.pan(x,y) in both MapView and StepInfoView?

Peter Lawrey Over a year ago

You can use a new Point(x, y) this way.

androidnotgenius Over a year ago

I really don't want to do all of my work solely in constructors. I want to be able to update scale without having to create new StepInfoViews.

androidnotgenius Over a year ago

I'm slowly starting to see the ugly reality.

|

Pete Kirkham · Accepted Answer · 2012-08-03 11:37:05Z

0

Move the scale field to the listener, and provide get and set.

In the view, hold a reference to the listener so you can access the scale.

For the MapView, register a different listener for each view instance so they have different scales.

For the StepInfoView, register the same listener for each view instance so they have the same scale. You could store the reference the listener in a static field.

answered Aug 3, 2012 at 11:37

Pete Kirkham

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1 Comment

Pete Kirkham Over a year ago

If you have two objects communicating, you need methods to allow them to communicate. Since you only have one value to communicate from the listener to the view, either you share a field between the two ( which as you have seen is brittle and causes duplication ) or you having a function where the value is either pushed to the view ( a setter) or a function where the value is pulled from the listener ( a getter, or a public field ). Having multiple views pull from the same listener is simpler than having a listener push to multiple views.

pepyakin · Accepted Answer · 2012-08-03 11:40:22Z

0

Why not to move scale field into the RootView class?

update: just got it. I think there is a place for aggregation: make some object container for stepinfo scale value, and pass thru StepInfoView's.

whatever, i think the simplest way it is to use getters.

edited Aug 3, 2012 at 11:40

answered Aug 3, 2012 at 11:34

pepyakin

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2 Comments

androidnotgenius Over a year ago

I need scale to be static in StepInfoView. If I make it static in the RootView, then the StepInfoViews and MapViews will not scale independently of each other.

androidnotgenius Over a year ago

"make some object container for stepinfo scale value, and pass thru StepInfoView's" I'm sorry, but I don't understand exactly what you're suggesting.

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