Why are two AtomicIntegers never equal?

by

This is partly because an AtomicInteger is not a general purpose replacement for an Integer.

The java.util.concurrent.atomic package summary states:

Atomic classes are not general purpose replacements for
java.lang.Integer and related classes. They do not define methods
such as hashCode and compareTo. (Because atomic variables are
expected to be mutated, they are poor choices for hash table keys.)

hashCode is not implemented, and so is the case with equals. This is in part due to a far larger rationale that is discussed in the mailing list archives, on whether AtomicInteger should extend Number or not.

One of the reasons why an AtomicXXX class is not a drop-in replacement for a primitive, and that it does not implement the Comparable interface, is because it is pointless to compare two instances of an AtomicXXX class in most scenarios. If two threads could access and mutate the value of an AtomicInteger, then the comparison result is invalid before you use the result, if a thread mutates the value of an AtomicInteger. The same rationale holds good for the equals method – the result for an equality test (that depends on the value of the AtomicInteger) is only valid before a thread mutates one of the AtomicIntegers in question.

More Related Contents:

  1. Why 2 return statements are mandatory in equals method
  2. What’s the difference between “.equals” and “==”? [duplicate]
  3. Why must wait() always be in synchronized block
  4. Any reason to prefer getClass() over instanceof when generating .equals()?
  5. How to share data with two(2) SwingWorker class in Java
  6. ConcurrentModificationException despite using synchronized
  7. Volatile vs Static in Java
  8. How to override equals method in Java
  9. When would you call java’s thread.run() instead of thread.start()?
  10. Getting an element from a Set
  11. Convert from List to CompletableFuture
  12. Why there is no ConcurrentHashSet against ConcurrentHashMap
  13. Using == operator in Java to compare wrapper objects
  14. Is there a Java utility to do a deep comparison of two objects? [closed]
  15. What are the main uses of yield(), and how does it differ from join() and interrupt()?
  16. What is the difference between synchronized on lockObject and using this as the lock?
  17. Hashcode and Equals for Hashset [duplicate]
  18. When should I use a CompletionService over an ExecutorService?
  19. When do I need to use AtomicBoolean in Java?
  20. Java ExecutorService: awaitTermination of all recursively created tasks
  21. Writing long and double is not atomic in Java?
  22. How to implement hashCode and equals method
  23. Why can’t we use ‘==’ to compare two float or double numbers [duplicate]
  24. Thread Confinement
  25. LinkedBlockingQueue vs ConcurrentLinkedQueue
  26. How to reduce java concurrent mode failure and excessive gc
  27. Does a breakpoint halt all threads?
  28. What is optimum thread pool size for simple program running cpu based tasks in Java
  29. How to combine 3 or more CompletionStages?
  30. When is it preferable to use volatile boolean in Java rather than AtomicBoolean? [duplicate]

Leave a Comment