HashMap in Java calculates hash based on the key of the inserted (key, value) pair and store its elements according to that. So essentially HashMap is an unordered collection but you may come across a scenario when you want to sort HashMap in Java. Sorting on HashMap can be done…
In this post we’ll see different ways to iterate a Map or HashMap in Java. One thing you should know is you can’t directly loop a Map in Java (except when you use forEach statement). There are methods that return a “collection view” of the Map using that view you…
HashMap in Java is the HashTable implementation of the Map interface and it is part of the Java Collections framework. HashMap class in Java extends AbstractMap class and implements Map, Cloneable and Serializable inerfaces. HashMap stores its elements as (key, value) pairs and to get a value you will need…
This post shows different ways to remove duplicate elements from ArrayList in Java. ArrayList in Java is designed to store repeated elements where as HashSet only store unique elements, using that feature of HashSet in Java you can remove duplicates from ArrayList. Only problem is HashSet is an unordered collection…
ConcurrentHashMap in Java is a thread safe Map implementation which provides another alternative to be used in a multithreaded environment apart from HashTable or explicitly synchronizing HashMap. ConcurrentHashMap is part of the java.util.concurrent package. Table of contents How is ConcurrentHashMap a better option Internal implementation of ConcurrentHashMap in Java Java…
If you have to store (key, value) pair in your Java application you will use one of the hash table based implementation present in java.util package and the options are HashMap, LinkedHashMap, TreeMap and HashTable. The Map implementation chosen by you will be based on the criteria whether synchronization is…
This post shows how to synchronize HashMap in Java and the HashMap’s thread safe alternative which can be used. HashMap is not thread safe If HashMap is accessed by multiple threads concurrently and at least one of the threads modifies the map structurally, you must synchronize HashMap externally. Note that…
This post talks about the ConcurrentSkipListMap class from the java.util.concurrent package and the interface ConcurrentNavigableMap this class implements. ConcurrentSkipListMap in Java ConcurrentSkipListMap is a thread-safe, scalable Map that stores its elements in sorted manner. By default map is sorted according to the natural ordering of its keys, or by a…
In Java 9 new static factory method has been added to create an immutable Map in Java. In this article we’ll see an example of creating immutable Map using factory method and how it makes it more convenient than the previous option of using Collections.unmodifiableMap(). You can not remove or…
TreeMap in Java is one of the implementation of the Map interface. How it differs from the other implementation HashMap is that unlike HashMap which is unordered, TreeMap is Sorted. TreeMap is sorted according to the natural ordering of its keys by default. If you want different sort ordering then…
