ConcurrentHashMap in Java?

by

The point is to provide an implementation of HashMap that is threadsafe. Multiple threads can read from and write to it without the chance of receiving out-of-date or corrupted data. ConcurrentHashMap provides its own synchronization, so you do not have to synchronize accesses to it explicitly.

Another feature of ConcurrentHashMap is that it provides the putIfAbsent method, which will atomically add a mapping if the specified key does not exist. Consider the following code:

ConcurrentHashMap<String, Integer> myMap = new ConcurrentHashMap<String, Integer>();

// some stuff

if (!myMap.contains("key")) {
  myMap.put("key", 3);
}

This code is not threadsafe, because another thread could add a mapping for "key" between the call to contains and the call to put. The correct implementation would be:

myMap.putIfAbsent("key", 3);

More Related Contents:

  1. Is iterating ConcurrentHashMap values thread safe?
  2. Why does ConcurrentHashMap prevent null keys and values?
  3. Recursive ConcurrentHashMap.computeIfAbsent() call never terminates. Bug or “feature”?
  4. String variable in java to get and store the json array in table column
  5. Unable to read a file
  6. Reverse a string in Java
  7. Where does the @Transactional annotation belong?
  8. How to import an existing X.509 certificate and private key in Java keystore to use in SSL?
  9. Selenium WebDriver throws Exception in thread “main” org.openqa.selenium.ElementNotInteractableException
  10. Java: Prefix/postfix of increment/decrement operators?
  11. Listening for input without focus in Java
  12. Android changing Floating Action Button color
  13. How to detect the timezone of a client?
  14. What is the difference between a local variable, an instance field, an input parameter, and a class field?
  15. Add an Background image to a Panel
  16. Converting a Java ArrayList of strings to a JavaScript array
  17. What is the purpose of ‘Class.forName(“MY_JDBC_DRIVER”)’?
  18. How to get the real path of Java application at runtime?
  19. JavaMail with Gmail: 535-5.7.1 Username and Password not accepted
  20. Create a mutable java.lang.String
  21. How to generate a graph of the dependency between all modules of a Maven project?
  22. PolyLine is not on the roads: it goes straight from one point to other
  23. How to use flood fill algorithm in Android?
  24. Lightweight Java Object cache API [closed]
  25. javax.crypto.BadPaddingException
  26. Hibernate sequence on oracle, @GeneratedValue(strategy = GenerationType.AUTO)
  27. Why does “split” on an empty string return a non-empty array?
  28. Rotate Image around character (JAVA)
  29. implicit super constructor Person() is undefined. Must explicitly invoke another constructor?
  30. Required @QueryParam in JAX-RS (and what to do in their absence)

Leave a Comment