Java Android program //easy

Dobrý deň nevie mi niekto kto sa trochu vyzná do javy povedať prečo mi nejde na androide tento program?

package com.example.projekt;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Point;
import android.os.Bundle;
import android.view.Display;
import android.view.View;

public class MainActivity extends AppCompatActivity {

    private CanvasView canvas;
    private int circleRadius = 30;
    private float circleX;
    private float circleY;
   
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Display display = getWindowManager().getDefaultDisplay();
        Point size = new Point();
        display.getSize(size);

        int screenWidth = size.x;
        int screenHeight = size.y;

        circleX = screenWidth / 2 - circleRadius;
        circleY = screenHeight / 2 - circleRadius;

        canvas = new CanvasView(MainActivity.this);
        setContentView(canvas);
    }

    private class CanvasView extends View{
        private Paint pen;

        public CanvasView(Context context){

            super(context);
            setFocusable(true);

            pen = new Paint();
        }


        public void OnDraw(Canvas screen){
            pen.setStyle(Paint.Style.FILL);
            pen.setAntiAlias(true);
            pen.setTextSize(30f);

            screen.drawCircle(circleX, circleY , circleRadius, pen);


        }
    }
}

Doplněn tag CODE (host)