Android Explicit and Implicit Intent

AppA MainActivity.java

package iterator.ir.appa;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {

    Button buttonShow;

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

        buttonShow= (Button) findViewById(R.id.buttonShow);

        buttonShow.setOnClickListener(buttonShow_OnClickListener);
    }

    View.OnClickListener buttonShow_OnClickListener=new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Intent intent=new Intent(getBaseContext(),MessageActivity.class);
            startActivity(intent);
        }
    };
}

AppA AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="iterator.ir.appa">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        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>
        <activity android:name=".MessageActivity">
            <intent-filter>
                <action android:name="ir.iterator.AppA.MessageActivity" />
                <category android:name="android.intent.category.DEFAULT" />
            </intent-filter>
        </activity>
    </application>

AppB MainActivity.java

package iterator.ir.appb;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {

    Button buttonShow;

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

        buttonShow= (Button) findViewById(R.id.buttonShow);
        buttonShow.setOnClickListener(buttonShow_OnClickListener);

    }

    View.OnClickListener buttonShow_OnClickListener=new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Intent intent=new Intent("ir.iterator.AppA.MessageActivity");
            startActivity(intent);
        }
    };
}

References
https://github.com/mhdr/AndroidSamples/tree/master/036