AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.superapp"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="16" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="com.example.superapp.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        
        <activity
            android:name="com.smartmobilesoftware.additionlibrary.CalculatorActivity" >
        </activity>
    </application>

</manifest>

CalculatorActivity.java

package com.smartmobilesoftware.additionlibrary;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;

public class CalculatorActivity extends Activity {

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

	@Override
	public boolean onCreateOptionsMenu(Menu menu) {
		// Inflate the menu; this adds items to the action bar if it is present.
		getMenuInflater().inflate(R.menu.activity_calculator, menu);
		return true;
	}

}

MainActivity.java

package com.example.superapp;

import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.view.Menu;
import android.view.View;

import com.smartmobilesoftware.additionlibrary.CalculatorActivity;


public class MainActivity extends Activity {

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

	@Override
	public boolean onCreateOptionsMenu(Menu menu) {
		// Inflate the menu; this adds items to the action bar if it is present.
		getMenuInflater().inflate(R.menu.activity_main, menu);
		return true;
	}
	
	/** Called when the user clicks the Send button */
	public void btnClick(View view) {
	    // Do something in response to button
		Intent intent = new Intent(this, CalculatorActivity.class);
		startActivity(intent);
		
	}

}