How to use WeakReference in Java and Android development?

java android weak-references
Chris picture Chris · Jul 14, 2010 · Viewed 92.1k times · Source

I have been a java developer for 2 years.

But I have never wrote a WeakReference in my code. How to use WeakReference to make my application more efficient especially the Android application?

Answer

dbyrne picture dbyrne · Jul 14, 2010

Using a WeakReference in Android isn't any different than using one in plain old Java. Here is a great guide which gives a detailed explanation: Understanding Weak References.

You should think about using one whenever you need a reference to an object, but you don't want that reference to protect the object from the garbage collector. A classic example is a cache that you want to be garbage collected when memory usage gets too high (often implemented with WeakHashMap).

Be sure to check out SoftReference and PhantomReference as well.

EDIT: Tom has raised some concerns over implementing a cache with WeakHashMap. Here is an article laying out the problems: WeakHashMap is not a cache!

Tom is right that there have been complaints about poor Netbeans performance due to WeakHashMap caching.

I still think it would be a good learning experience to implement a cache with WeakHashMap and then compare it against your own hand-rolled cache implemented with SoftReference. In the real world, you probably wouldn't use either of these solutions, since it makes more sense to use a 3rd party library like Apache JCS.

Related questions

Android Asyntask: Use weak reference for context to avoid device rotate screen

In Apress Pro Android 4 the author has said that: [...] context of currently running activity will no longer be valid when the device is rotated. [...] One approach is to use a weak reference to the activity instead of a hard reference [...] …

Read More
WeakReference/AsyncTask pattern in android

I have a question regarding this simple frequently occurring situation in android . We have a main activity , we invoke an AsyncTask alongwith the reference of the mainactivity , so that that the AsyncTask can update the views on the MainActivity. I …

Read More
HashMap with weak values

I'm implementing a cache for Objects stored persistently. The idea is: Method getObjectFromPersistence(long id); ///Takes about 3 seconds Method getObjectFromCache(long id) //Instantly And have a method: getObject(long id) with the following pseudocode: synchronized(this){ CustomObject result= getObjectFromCache(id) …

Read More