Does setting Java objects to null do anything anymore?

by

It depends a bit on when you were thinking of nulling the reference.

If you have an object chain A->B->C, then once A is not reachable, A, B and C will all be eligible for garbage collection (assuming nothing else is referring to either B or C). There’s no need, and never has been any need, to explicitly set references A->B or B->C to null, for example.

Apart from that, most of the time the issue doesn’t really arise, because in reality you’re dealing with objects in collections. You should generally always be thinking of removing objects from lists, maps etc by calling the appropiate remove() method.

The case where there used to be some advice to set references to null was specifically in a long scope where a memory-intensive object ceased to be used partway through the scope. For example:

{
  BigObject obj = ...
  doSomethingWith(obj);
  obj = null;             <-- explicitly set to null
  doSomethingElse();
}

The rationale here was that because obj is still in scope, then without the explicit nulling of the reference, it does not become garbage collectable until after the doSomethingElse() method completes. And this is the advice that probably no longer holds on modern JVMs: it turns out that the JIT compiler can work out at what point a given local object reference is no longer used.

More Related Contents:

  1. How can I read a large text file line by line using Java?
  2. How can I avoid garbage collection delays in Java games? (Best Practices) [closed]
  3. Which loop has better performance? Why?
  4. Garbage collection behaviour for String.intern()
  5. Know of any Java garbage collection log analysis tools? [closed]
  6. Java Collections and Garbage Collector
  7. What is the Metadata GC Threshold and how do I tune it?
  8. Java very large heap sizes [closed]
  9. What GC parameters is a JVM running with?
  10. Measuring time spent on GC
  11. What are the effects of exceptions on performance in Java?
  12. Java Reflection Performance
  13. Efficient way to do batch INSERTS with JDBC
  14. If profiler is not the answer, what other choices do we have?
  15. What is the fastest way to compare two sets in Java?
  16. What are the pros and cons of performing calculations in sql vs. in your application
  17. StringBuilder/StringBuffer vs. “+” Operator
  18. When will JVM use intrinsics
  19. Why is System.nanoTime() way slower (in performance) than System.currentTimeMillis()?
  20. Java still uses system memory after deallocation of objects and garbage collection
  21. Java: A two dimensional array is stored in column-major or row-major order?
  22. Thread Caching and Java Memory model
  23. What’s wrong with using associativity by compilers?
  24. How do you calculate log base 2 in Java for integers?
  25. Will .hashcode() return a different int due to compaction of tenure space?
  26. PreparedStatements and performance
  27. Java application profiling
  28. How do you Force Garbage Collection from the Shell?
  29. How can I profile my Android app? [closed]
  30. Performance of WebView in JavaFX

Leave a Comment