Request one permission on Android

RequestPermission.java

package isabelle.com.requestpermissiondemo;

import android.Manifest;
import android.annotation.TargetApi;
import android.content.DialogInterface;
import android.content.pm.PackageManager;
import android.os.Build;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {
    private final String TAG = MainActivity.class.getSimpleName();

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

        insertDummyContactWrapper();
    }

    final private int REQUEST_CODE_ASK_PERMISSIONS = 123;

    @TargetApi(Build.VERSION_CODES.M)
    private void insertDummyContactWrapper() {
        int hasWriteContactsPermission = checkSelfPermission(Manifest.permission.WRITE_CONTACTS);
        if (hasWriteContactsPermission != PackageManager.PERMISSION_GRANTED) {
            if (!shouldShowRequestPermissionRationale(Manifest.permission.WRITE_CONTACTS)) {
                showMessageOKCancel("You need to allow access to Contacts",
                        new DialogInterface.OnClickListener() {
                            @Override
                            public void onClick(DialogInterface dialog, int which) {
                                requestPermissions(new String[] {Manifest.permission.WRITE_CONTACTS},
                                        REQUEST_CODE_ASK_PERMISSIONS);
                            }
                        });
                return;
            }
            requestPermissions(new String[] {Manifest.permission.WRITE_CONTACTS},
                    REQUEST_CODE_ASK_PERMISSIONS);
            return;
        }
        Toast.makeText(this, "Insert contact", Toast.LENGTH_SHORT).show();
    }

    private void showMessageOKCancel(String message, DialogInterface.OnClickListener okListener) {
        new AlertDialog.Builder(MainActivity.this)
                .setMessage(message)
                .setPositiveButton("OK", okListener)
                .setNegativeButton("Cancel", null)
                .create()
                .show();
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
        switch (requestCode) {
            case REQUEST_CODE_ASK_PERMISSIONS:
                if (grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                    // Permission Granted
                    Toast.makeText(this, "Insert contact", Toast.LENGTH_SHORT).show();
                } else {
                    // Permission Denied
                    Toast.makeText(MainActivity.this, "WRITE_CONTACTS Denied", Toast.LENGTH_SHORT)
                            .show();
                }
                break;
            default:
                super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        }
    }
}