Option Menu

Option Menu
The options menu is the primary collection of menu items for an activity.
It's use where you should place actions on the app, such as "Search," "Compose email," and "Settings."
 
activity_main.xml

<?xml version="1.0" encoding="utf-8"?> 

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

 xmlns:app="http://schemas.android.com/apk/res-auto"

 xmlns:tools="http://schemas.android.com/tools"

 android:layout_width="match_parent"

 android:layout_height="match_parent"

 android:orientation="vertical"

 tools:context="com.example.dell.optionmenu.MainActivity">
 

<TextView

 android:text="Click the three dots appearing above in ActionBar"

 android:layout_width="match_parent"

 android:layout_height="wrap_content"       

 android:id="@+id/textView"

 style="@android:style/TextAppearance.DeviceDefault.Large"/>
 

</LinearLayout>

add menu items in menu files 

app>>res>>values>>menu

<?xml version="1.0" encoding="utf-8"?><menu xmlns:android="http://schemas.android.com/apk/res/android">
<item android:id="@+id/item1" android:title="Item1"/>
<item android:id="@+id/item2" android:title="Item2"/>
<item android:id="@+id/item3" android:title="Item3"/>
</menu> 

MainActivity.java 

import android.Manifest;
import android.content.Context;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.net.Uri;
import android.support.v4.app.ActivityCompat;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.Toast;


        public class MainActivity extends AppCompatActivity {
            Button btn;
            EditText numTxt;
            String sNum;

            @Override 

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

            @Override 

            public boolean onCreateOptionsMenu(Menu menu) {
                getMenuInflater().inflate(R.menu.menu_main,menu);
                return true;
            }

            @Override 

            public boolean onOptionsItemSelected(MenuItem item) {
                switch (item.getItemId()) {
                    case R.id.item1:
                        Toast.makeText(this, "Item 1 is Selected", Toast.LENGTH_SHORT).show();
                        return true;

                    case R.id.item2:
                        Toast.makeText(this,"Item 2 is Selected",Toast.LENGTH_SHORT).show();
                        return true;

                    case R.id.item3:
                        Toast.makeText(this,"Item 3 is Selected",Toast.LENGTH_SHORT).show();
                        return true;

                    default:
                        return super.onOptionsItemSelected(item);
                }
            }
        }