An android app has some limitations when it comes to memory availability. Unlike a normal Java app, you do not have luxury of expanding memory your application uses, as it will be completely dependent on the device on which the app is running, memory available in the phone, number of applications running simultaneously. We will not have control over these external factors so we will need to optimize memory usage on our end.

Some of the techniques I used in one of my last projects which used a lot of images/ bitmaps and hence ran into many memory issues.

• Use of flags: Set android:hardwareAccelerated=”true” and android:largeHeap=”true” flags in manifest file. Downside is that these flags are only available after android 3.0. More than 50% of android devices still run on gingerbread (2.3+), so this is not a very reliable solution if you are targeting a larger audience. Though worth a try for high end (3.0+) devices.
• Memory leakage: DVM grabage collection works n principle of JVM garbage collection, that is it will reclaim the memory for an object if there is no reference to it. So make sure when you are done with an object and do not need it anymore, mark the object reference as null.
• Use minimum space for an object: Design your classes intelligently, for example if you are handling student data and you address details will not be used frequently, create a separate class and initialize the object only when it is required. Remember, if a char can work, don;t use int or long.
• Objects are always placed on heap: One of my colleagues was wondering that how can an object occupy space, after the method exits, if the object is declared inside a method. Remember, only references are stored in the stack for method, the actual object is always stored in the heap. So the memory will be freed only when next cycle of garbage collection occurs
• Use Garbage collection: You can call system.gc(); to initiate garbage collection, but this only suggests JVM/DVM to run a garbage collection, you cannot force it.
• Playing with Bitmaps/ Images: Bitmaps and images take highest amount of memory, so make sure you recycle() bitmaps as soon as you are done using it. Make sure you have removed all references (imageviews/ objects) to bitmap before calling recycle().
• Handle Activity Stack: If the app can be used back and forth multiple times, it is better to handle the back-front flow in the code, as default back button handling in android needs to keep a tack of activity stack and uses memory for that. Simplest will be to call previous activity on back button through code and always finish current activity before moving to next.