* to throw a ConcurrentModificationException.

Case 2: After the creation of an iterator, the Collection is internally modified by any method other than the iterator’s own methods for removal and addition.Įxample_v2.java: import The exception is thrown because we change the internal structure of the HashMap by removing an existing key, while we iterating over it. Case 1: The Collection is internally modified, while a thread is iterating over it.Įxception in thread 'main' Īt $HashIterator.nextEntry(HashMap.java:926)Īt $KeyIterator.next(HashMap.java:960)Īt (Example.java:18) In this section, we will describe and explain those cases that produce a. The exception is thrown even one thread is violating an object’s contract. Notice that this exception does not indicate that the object has been concurrently modified by a different thread. These iterators are called fail-fast iterators, as they stop the normal execution to report an error, rather than continuing in a non-deterministic way. Some iterators throw a when they detect such behavior. In general, the results of the iteration are undefined. An example of not permissible behavior is when a thread tries to modify the internal structure of a Collection, while another thread is iterating over it. The is a RuntimeException that may be thrown by methods that have detected concurrent modification of an object when such modification is not permissible.

Java utility for itr