How to check grant permission at run-time in android?

This example demonstrates how do I check grant permission at un-time in android.
Step 1 − Create a new project in Android Studio, go to File ⇒ New Project and fill all required details to create a new project.
Step 2 − Add the following code to res/layout/activity_main.xml.
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
   xmlns:tools="http://schemas.android.com/tools"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   tools:context=".MainActivity">
   <TextView
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_centerInParent="true"
      android:text="Grant permissions at run-time..."
      android:textSize="16sp"
      android:textStyle="bold"/>
</RelativeLayout>
Step 3 − Add the following code to src/MainActivity.java
import android.Manifest;
import android.content.pm.PackageManager;
import android.os.Build;
import android.support.annotation.NonNull;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v4.app.ActivityCompat;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity{
   private static final int REQUEST_PERMISSION_CODE = 101;
   @Override
   protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
         if (ActivityCompat.checkSelfPermission(this, Manifest.permission.ANSWER_PHONE_CALLS)!=PackageManager.PERMISSION_GRANTED) {
            ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.ANSWER_PHONE_CALLS}, REQUEST_PERMISSION_CODE);
         }
      }
   }
   @Override
   public void onRequestPermissionsResult(int requestCode, @NonNull String permissions[], @NonNull int[] grantResults) {
      switch (requestCode) {
         case REQUEST_PERMISSION_CODE: {
            if (grantResults[0] == PackageManager.PERMISSION_GRANTED) {
               Toast.makeText(this, "Permission Granted..", Toast.LENGTH_SHORT).show();
            } else {
               Toast.makeText(this, "Permission Denied..", Toast.LENGTH_SHORT).show();
            }
         }
      }
   }
}
Step 4 − Add the following code to androidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="app.com.sample">
   <uses-permission android:name="android.permission.ANSWER_PHONE_CALLS"/>
   <application
      android:allowBackup="true"
      android:icon="@mipmap/ic_launcher"
      android:label="@string/app_name"
      android:roundIcon="@mipmap/ic_launcher_round"
      android:supportsRtl="true"
      android:theme="@style/AppTheme">
      <activity android:name=".MainActivity">
         <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
         </intent-filter>
      </activity>
   </application>
</manifest>
Let's try to run your application. I assume you have connected your actual Android Mobile device with your computer. To run the app from android studio, open one of your project's activity files and click Run  icon from the toolbar. Select your mobile device as an option and then check your mobile device which will display your default screen –
Click here to download the project code.