How to avoid copy-paste when create similar classes in Java

Question

I have created a custom MyAspectButton that keeps the aspect:

public class MyAspectButton extends Button
{
    private float m_aspect = -1.f;

    // ...
    // ... Constructors, setters/getters ...
    // ...

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec)
    {
        if (aspect >= 0.f)
        {
            super.onMeasure(widthMeasureSpec, heightMeasureSpec);
            final int measuredWidth = getMeasuredWidth();
            widthMeasureSpec = MeasureSpec.makeMeasureSpec(measuredWidth, MeasureSpec.EXACTLY);
            heightMeasureSpec = MeasureSpec.makeMeasureSpec(Math.round(measuredWidth * aspect), MeasureSpec.EXACTLY);
        }
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    }
}

Now I want to have MyAspectLinearLayout, MyAspectRelativeLayout, and so on. Their onMeasure method will be the same.

How can I implement a bunch of these classes with as little copy-paste as possible?

I am aware of a concept of generic classes in Java, but here I would have to inherit from template parameter that compiler does not let me to do:

public class MyAspectWidget<T> extends T
{
    // ...
}

does not compile.

just write this measurement logic in standalone static class and use its methods at the onMeasure — nikis
– nikis, Commented Apr 25, 2015 at 13:11
@user2418306 this won't work, because OP already has base classes: Button, RelativeLayout, LinearLayout and so on. — nikis
– nikis, Commented Apr 25, 2015 at 13:13
@nikis AbstractLayoutButton extends Button, SpecificLayoutButton extends AbstractLayoutButton. Explain to me why this won't work? — user2418306
– user2418306, Commented Apr 25, 2015 at 13:18
@user2418306 and how does it solve the issue? every time in AbstractLayoutButton, AbstractLinearLayout, AbstractRelativeLayout he will have to copy-paste the same measurement code. — nikis
– nikis, Commented Apr 25, 2015 at 13:21
@nikis My bad. I thought OP wants a bunch of buttons for different layouts. Though Button and Layout are not similar classes, are they? — user2418306
– user2418306, Commented Apr 25, 2015 at 13:39

Ian Kemp - SO dead by AI greed · Accepted Answer · 2015-04-25 13:18:02Z

1

If I'm understanding correctly, you want to inherit from a bunch of different base classes, but apply the same behaviour to all of them:

MyAspectButton extends Button
MyAspectLinearLayout extends LinearLayout
MyAspectRelativeLayout extends RelativeLayout

What you are looking for is multiple inheritance, which Java does not support. Your only option is to have a single class that performs the measuring logic, which each of your child classes' onMeasure method call into:

public class MyAspectButton extends Button
{
    private float m_aspect = -1.f;

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec)
    {
        super.onMeasure(MyMeasuringClass.MeasureWidth(this, widthMeasureSpec), MyMeasuringClass.MeasureHeight(this, heightMeasureSpec));
    }
}

answered Apr 25, 2015 at 13:18

Ian Kemp - SO dead by AI greed

1

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1 Comment

Nick Over a year ago

I also want to read m_aspect from attributes in public MyAspectButton(Context context, AttributeSet set). If I undestand you correcly, I will have to copy-paste all this stuff in all the custom classes as well?

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