ConcurrentModificationException with LinkedHashMap

Question

Not sure what is triggering a java.util.ConcurrentModificationException when I iterate over the LinkedHashMap structure in the code below. Using the

Answer 1

You're using an access-ordered linked hash map: from the spec at http://docs.oracle.com/javase/7/docs/api/java/util/LinkedHashMap.html,

A structural modification is any operation that adds or deletes one or more mappings or, in the case of access-ordered linked hash maps, affects iteration order. In insertion-ordered linked hash maps, merely changing the value associated with a key that is already contained in the map is not a structural modification. In access-ordered linked hash maps, merely querying the map with get is a structural modification.)

Simply calling get is enough to be considered a structural modification, triggering the exception. If you use the entrySet() sequence you're only querying the entry and NOT the map, so you don't trigger the ConcurrentModificationException.