In what situations and why does memory leak occur in an application?

Memory leaks in an application occur when memory allocated for objects is no longer needed but is not released by the system because there are still references to these objects. In Android, this often happens due to:

• Long-lived references to the Activity or View context, which prevent the garbage collector from freeing memory after the Activity is destroyed.
• Use of static variables that hold references to objects with a short lifecycle.
• Incorrect use of listeners and callbacks that are not unsubscribed.
• Improper management of threads and asynchronous tasks that continue to reference objects.

For example, if an anonymous Runnable class referencing an Activity is created in an Activity and not canceled upon destruction, the Activity will not be garbage collected, leading to a memory leak.