A NavigableMap in Java extends a SortedMap with navigation methods returning the closest matches for given search targets. Methods lowerEntry, floorEntry, ceilingEntry, and higherEntry return Map.Entry objects associated with keys respectively less than, less than or equal, greater than or equal, and greater than a given key, returning null if there is no such key. Similarly, […]
Introduction Here we will see an example on creating a custom HashMap in Java. We have seen the built-in implementation of HashMap in Java API and we know how HashMap works and its usages. The intention of this example is not to create a rigid HashMap that provides the same functionalities as Java API provides […]
Suppose we have keys as strings and values as list of objects in a HashMap. Now we want to iterate list of objects and want make one attribute of the object as keys and other attribute(s) as values and want to put as key/value pairs in another map. So this example is going to show […]
Introduction In this tutorial, I will show you how you are going to collect and convert objects using lambda expression in Java 8 stream API. We will collect objects and map to another custom objects using Java 8 stream API with the help of Lambda Expression. Suppose you have entity classes generated from your database […]
This tutorial will show you how to use Java 8 stream API’s filter and map methods. filter() method is used to produce a stream containing only a certain type of objects into the result output and map() method is used to transform a stream from one type to another type into the result output.
In this tutorial I will show you how to use Comparator to sort values in HashMap.
Introduction In custom object as a key in hashmap example, I will show you how to work with user defined objects as keys in Map. To use user defined objects as keys in Map you need to tell Java how to compare user defined objects by overriding the hashCode() and equals() methods. Most of the […]
What is WeakHashMap WeakHashMap is based on Hash table implementation of the Map interface but with weak keys. An entry in a WeakHashMap will automatically be removed when its key is no longer in ordinary use. When a key has been discarded due to weakness characteristics of keys its entry is effectively removed from the […]
What is TreeMap It is a Red-Black tree based NavigableMap implementation. Like HashMap it contains only unique elements. Unlike HashMap it cannot have null key but like HashMap it can have multiple null values. The map is sorted according to the natural ordering (ascending order) of its keys, or by a Comparator provided at map […]
What is LinkedHashMap A LinkedHashMap like HashMap is a simple yet powerful way to store and get data. Unlike HashMap, LinkedHashMap is based on HashTable and Linked list implementation of the Map interface and stores items as key/value pairs. Like HashMap, LinkedHashMap permits only unique keys. It also permits only one null key (whereas HashTable […]