[Android] TestAsyncTask

package com.example.doremi.myapplication;

import android.os.AsyncTask;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {
    private Button btnStart, btnStop;
    private boolean IS_RUN = false;
    private int Counter = 0;

    class TestAsyncTask extends AsyncTask<String, Integer, Integer> {
        @Override
        protected Integer doInBackground(String... params) {
            for (int i = 0; i < 1000000; i++) { Counter++; }
            return null;
        }

        @Override
        protected void onProgressUpdate(Integer... values) {
            super.onProgressUpdate(values);
        }

        @Override
        protected void onPostExecute(Integer result) {
            super.onPostExecute(result);
            if (IS_RUN) { new TestAsyncTask().execute((String[]) null); }
            Toast.makeText(getApplicationContext(), String.valueOf(Counter), Toast.LENGTH_SHORT).show();
        }

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
        }
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        btnStart = (Button)findViewById(R.id.button);
        btnStart.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                IS_RUN = true;
                new TestAsyncTask().execute((String[]) null);
            }
        });

        btnStop = (Button)findViewById(R.id.button2);
        btnStop.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                IS_RUN = false;
                new TestAsyncTask().execute((String[]) null);
            }
        });
    }
}