How to use Bluetooth On/Off in Android

MainActivity.java

This activity shows bluetooth Adapter for turn on Bluetooth devices.

package com.example.icowboysradio.myapplication;

import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ListView;
import android.widget.Toast;

import java.util.ArrayList;
import java.util.Set;

public class MainActivity extends AppCompatActivity {

    Button button1,button2,button3,button4;
    private BluetoothAdapter bluetoothAdapter;
    private Set pairedDevices;
    ListView listView;

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

        button1 = (Button) findViewById(R.id.btn_turnon);
        button2=(Button)findViewById(R.id.btn_visible);
        button3=(Button)findViewById(R.id.btn_list);
        button4=(Button)findViewById(R.id.btn_turnoff);

        bluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
        listView = (ListView)findViewById(R.id.listView);
    }

    public void on(View v){
        if (!bluetoothAdapter.isEnabled()) {
            Intent turnOn = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
            startActivityForResult(turnOn, 0);
            Toast.makeText(getApplicationContext(), "Bluetooth Turns on",Toast.LENGTH_LONG).show();
        } else {
            Toast.makeText(getApplicationContext(), "Already Bluetooth gets on", Toast.LENGTH_LONG).show();
        }
    }

    public void off(View v){
        bluetoothAdapter.disable();
        Toast.makeText(getApplicationContext(), "Bluetooth Turns off" ,Toast.LENGTH_LONG).show();
    }


    public  void visible(View v){
        Intent getVisible = new Intent(BluetoothAdapter.ACTION_REQUEST_DISCOVERABLE);
        startActivityForResult(getVisible, 0);
    }


    public void list(View v){
        pairedDevices = bluetoothAdapter.getBondedDevices();

        ArrayList list = new ArrayList();

        for(BluetoothDevice bluetoothDevice : pairedDevices) list.add(bluetoothDevice.getName());
        Toast.makeText(getApplicationContext(), "Bluetooth Connected devices",Toast.LENGTH_SHORT).show();

        final ArrayAdapter adapter = new  ArrayAdapter(this,android.R.layout.simple_list_item_1, list);

        listView.setAdapter(adapter);
    }
}