activity_main.xmlMainActivity.java
<?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"
    android:padding="16dp"
    tools:context="com.codinginflow.multiautocompletetextviewexample.MainActivity">

    <MultiAutoCompleteTextView
        android:id="@+id/mactv"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:completionThreshold="1"
        android:hint="Select countries" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:onClick="showInput"
        android:text="Show input" />

</LinearLayout>
package com.codinginflow.multiautocompletetextviewexample;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.MultiAutoCompleteTextView;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {
    private static final String[] COUNTRIES = new String[]{
            "Afghanistan", "Albania", "Algeria", "Andorra", "Angola"
    };

    private MultiAutoCompleteTextView editText;

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

        editText = findViewById(R.id.mactv);
        ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
                android.R.layout.simple_list_item_1, COUNTRIES);
        editText.setAdapter(adapter);
        editText.setTokenizer(new MultiAutoCompleteTextView.CommaTokenizer());
    }

    public void showInput(View v) {
        String input = editText.getText().toString().trim();
        String[] singleInputs = input.split("\\s*,\\s*");

        String toastText = "";

        for (int i = 0; i < singleInputs.length; i++) {
            toastText += "Item " + i + ": " + singleInputs[i] + "\n";
        }

        Toast.makeText(this, toastText, Toast.LENGTH_SHORT).show();
    }
}