How to Disable Back button in android

/**
* To disable back button(when click back button nothing happen)
*/
@Override
public void onBackPressed() {
  return;
}

How to Launch Activities from different application in android

For Example We have two application with same package and Different Namespace.

First Application: Com.Example.Application1

Second Application: Com.Example.Application2

In this case you can define common Manifest file for both Application1 and Application2 as given below

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

    package="Com.Example">

And add given line to your manifest file

<activity android:name=".Application2/Activity2">
  <intent-filter>
    <action android:name="Application2.intent.action.Launch" />
    <category android:name="android.intent.category.DEFAULT" />
  </intent-filter>
</activity>

Now you can create an Intent to launch Activity2 from the Activity1 with this line of code:

Intent intent = new Intent("Application2.intent.action.Launch");

startActivity(intent);