- The standard definition of a memory leak is a scenario that occurs when objects are no longer being used by the application, but the Garbage Collector is unable to remove them from working memory – because they’re still being referenced.
- As a result, the application consumes more and more resources – which eventually leads to a fatal OutOfMemoryError.
- We will see a few scenarios.
- Instead of taking the primitive long for the sum, we took the Long (wrapper class), which is the cause of the memory leak.
- Due to auto-boxing, sum=sum+l; creates a new object in every iteration, so 1000 unnecessary objects will be created.
- Here, a memory leak occurs due to the internal map data structure. This class is to display the employee value from the cache.
- Once those are displayed, there is no need to store those elements in the cache.
- We forgot to clear the cache, so although objects in cache are not required anymore by the application, it can’t be GCed, as map holds a strong reference to them.
- Alternatively, you can initialize the cache by WeakHashMap.
- The beauty of WeakHashMap is, if keys are not referenced by any other objects, then that entry will be eligible for GC.
- In the above example, we close the connection (Costly) resource in the try block, so in the case of an exception, the connection will not be closed.
- So it creates a memory leak as this connection never returns back to the pool.
- Please always put any closing stuff in the finally block.
- As in CustomKey, we forgot to provide equals() and hashcode() implementation, so a key and value stored in the map can’t be retrieved later, as the map get() method checks hashcode() and equals().
- But this entry is not able to be GCed, as the map has a reference to it, but application can’t access it. Definitely a memory leak.
- So when you make your Custom key, always provide an equals and hashcode() implementation.