Cannot refer to the non-final local variable button defined in an enclosing scope, Random method error

Question

I am getting an error in my project with eclipse:

Cannot refer to the non-final local variable button defined in an enclosing scope

This my class:

import android.app.Activity;
import android.content.Context;
import android.graphics.Point;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.widget.Button;
import android.view.Menu;
import android.view.MenuItem;
import android.view.WindowManager;

import java.util.Random;
import java.util.Timer;
import java.util.TimerTask;

public class MainActivity extends Activity {
Button buttonblack;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

     buttonblack = (Button)findViewById(R.id.Button01);

     startRandomButton(buttonblack);    

}

public static Point getDisplaySize(@NonNull Context context) {
    Point point = new Point();
    WindowManager manager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
    manager.getDefaultDisplay().getSize(point);
    return point;
}

private void setButtonRandomPosition(Button button){
    int randomX = new Random().nextInt(getDisplaySize(this).x);
    int randomY = new Random().nextInt(getDisplaySize(this).y);

    button.setX(randomX);
    button.setY(randomY);
}

private void startRandomButton(Button button) {
    Timer timer = new Timer();
    timer.schedule(new TimerTask() {
        @Override
        public void run() {
            setButtonRandomPosition(button);
        }
    }, 0, 1000);//Update button every second
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();
    if (id == R.id.action_settings) {
        return true;
    }
    return super.onOptionsItemSelected(item);
}
}

The problem is in this method:

private void startRandomButton(Button button) {
        Timer timer = new Timer();
        timer.schedule(new TimerTask() {
            @Override
            public void run() {
                setButtonRandomPosition(button);// Cannot refer to the non-final local variable button defined in an enclosing scope
            }
        }, 0, 1000);//Update button every second
    }

Can someone help me fix this? Or suggest any other code that could be better than this?

Answer 1

Change your code to private void startRandomButton(final Button button) . The compiler wants to make sure that a reference is not being re-assigned inside a method of an anonymous class .

From java-8, If your reference is effectively-final , then you don't even have to mark those arguments as final

Answer 2

You have declared Button buttonblack; Globally in MainActivity ..

you can pass buttonblack like this setButtonRandomPosition(buttonblack); without referring it as final .