Android says farewell to the menu button
With Android 4.0 (Ice Cream Sandwich), Google wants app developers to remove dependencies on the menu button used on existing devices. Instead, developers are being asked to migrate their programs to use the ActionBar class introduced in Android 3.0. Writing on the Android developers blog, Scott Main explains that this is to help ensure a consistent user experience as Ice Cream Sandwich becomes available on more devices. Android 3.0 or later currently runs on only 3.9% of current Android devices.
Source: Google If an app developed for Android 2.3 or earlier runs on Android 3.0 or later, an icon with three dots is displayed to the right of the action bar. This is the "action overflow", which can be used to access actions which would otherwise be displayed using the physical button. This also appears even if the app doesn't use the options menu – this behaviour is, says Main, unnecessarily confusing for users and is another reason to update legacy apps.
In the blog post, Main provides simple code snippets to demonstrate the work required to migrate from the old menu button to the new action bar, but the process does also involve developers considering how to place actions and options in the interface. A detailed developers' guide to the action bar is also available.