Login Session - Activities
public class SampleApplication extends Application {

private static String username;
private static String password;

@Override
public void onCreate() {
    super.onCreate();
    username="";
    password="";
}

public static String getUsername() {
    return username;
}

public static void setUsername(String username) {
    SampleApplication.username = username;
}

public static String getPassword() {
    return password;
}

public static void setPassword(String password) {
    SampleApplication.password = password;
}


}

<application
    android:name=".SampleApplication"
    android:icon="@drawable/icon" android:label="@string/app_name">
    <activity android:name=".SampleApp"
              android:label="@string/app_name"
              >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>

</application>

SampleApplication.setUsername("");
String currentUserName=SampleApplication.getUsername();
SampleApplication.setPassword("");
String currentPassword=SampleApplication.getPassword();

private String username;
private String password;

@Override
public void onCreate() {
    super.onCreate();
    username="";
    password="";
}

public String getUsername() {
    return username;
}

public void setUsername(String username) {
    SampleApplication.username = username;
}

public String getPassword() {
    return password;
}

public void setPassword(String password) {
    SampleApplication.password = password;
}


}

((SampleApplication )getApplication()).getUsername();