How do I fix ConcurrentModificationException in Java?

What causes Java Util ConcurrentModificationException?

The java. util. ConcurrentModificationException is typically thrown when code attempts to modify a data collection while that collection is actively in use, such as being iterated.

Which method of iterator throws ConcurrentModificationException?

If we invoke a sequence of methods on an object that violates its contract, then the object throws ConcurrentModificationException. For example: if while iterating over the collection, we directly try to modify that collection, then the given fail-fast iterator will throw this ConcurrentModificationException.

How do I remove Java Util ConcurrentModificationException?

To Avoid ConcurrentModificationException in single-threaded environment. You can use the iterator remove() function to remove the object from underlying collection object. But in this case, you can remove the same object and not any other object from the list.

How do you prevent ConcurrentModificationException on a map?

make your POJOs thread-safe and do data updates on POJOs directly. use ConcurrentHashMap. keep on using simple HashMap, but build a new map on each modification and switch maps behind the scenes (synchronizing the switch operation or using AtomicReference)

What is fail safe in Java?

Fail-safe iterators allow modifications of a collection while iterating over it. These iterators don’t throw any Exception if a collection is modified while iterating over it. They use copy of original collection to traverse over the elements of the collection.

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How do I get ConcurrentModificationException?

The ConcurrentModificationException will occur if you try to modify the structure of the original list with the subList. Let’s see this with a simple example. List < String > names = new ArrayList. names.

Can we iterate HashMap?

There is a numerous number of ways to iterate over HashMap of which 5 are listed as below: Iterate through a HashMap EntrySet using Iterators. Iterate through HashMap KeySet using Iterator. Iterate HashMap using for-each loop.

What is iterator in Java?

Iterator in Java. In Java, an Iterator is one of the Java cursors. Java Iterator is an interface that is practiced in order to iterate over a collection of Java object components entirety one by one. … The Java Iterator also helps in the operations like READ and REMOVE.

What is fail safe and fail fast in Java?

Fail-safe iterators means they will not throw any exception even if the collection is modified while iterating over it. … Whereas Fail-fast iterators throw an exception(ConcurrentModificationException) if the collection is modified while iterating over it.

What is difference between HashMap and ConcurrentHashMap in Java?

HashMap is non-Synchronized in nature i.e. HashMap is not Thread-safe whereas ConcurrentHashMap is Thread-safe in nature. HashMap performance is relatively high because it is non-synchronized in nature and any number of threads can perform simultaneously.

Can we remove an element by using for each loop?

The program needs access to the iterator in order to remove the current element. The for-each loop hides the iterator, so you cannot call remove .

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