inner class non-final variable java

Question

I needed to change variables inside an inner class and I got the infamous "Cannot refer to a non-final variable inside an inner class defined in a different method" error.

void onStart(){
  bt.setOnClickListener(new View.OnClickListener() {
     public void onClick(View v) {
       int q = i;
     }
  });
}

I quickly made a class that held all of the things I wanted to change and made a final version of the class outside the inner class

class temp{
  int q;
}

void onStart(){
  final temp x = new temp();
  bt.setOnClickListener(new View.OnClickListener() {
     public void onClick(View v) {
       x.q = i;
     }
  });
}

This seems to be what I need and it works but I am wondering if this is how to correctly work around the problem. Also, I really hate using the word temp to name my class. Is there an actual programming term for what I did so that I make a more descriptive name for my class?

Answer 1

You can simply create an inner class instead of an anonymous one (like you are currently doing). Then you have a constructor and any other methods you want to set your members. No hackiness required (like the array of 1 case).

I find this cleaner if the class requires any exchange of data with its outer class, but admit it is a personal preference. The array of 1 idiom will work as well and is more terse, but frankly, it just looks fugly. I typically limit anonymous inner classes to those that just perform actions without trying to update data in the outer class.

For example:

private MyListener listener = new MyListener();

void onStart(){
  bt.setOnClickListener(listener);
}

class MyListener implements OnClickListener
{ 
    String name;
    int value;

    void setName(String newName)
    {
        name = newName;
    }

    void setValue(int newValue)
    {
        value = newValue;
    }

    public void onClick(View v) 
    {
        // Use the data for some unknown purpose
    }
}

If there are multiple threads involved, then appropriate synchronization will have to be used as well.