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Java Assertion: The ‘assert’ Keyword Example

Java assert statements contain a boolean expression that must be true when the assertion executes. If it is not true, it will throw an AssertionError.

Java Abstract Classes and Methods

Java abstract keyword can be used with classes and methods; but not with variables. abstract is non-access modifier which helps in achieving abstraction.

Java Flow Control Statements

In Java, control flow statements help in conditionally executing statements based on whether the evaluation result is true or false.

Java CopyOnWriteArraySet class

CopyOnWriteArraySet is a thread-safe Set in Java. It ensures safe concurrent access by creating a new copy of the internal array for each modification.

Java CopyOnWriteArrayList class

Java CopyOnWriteArrayList is a thread-safe variant of ArrayList in which all mutative operations (add, set, and so on) are implemented by making a fresh copy of the underlying array. It’s immutable snapshot style iterator method uses a reference to the state of the array at the point that the iterator …

Java TransferQueue Vs. LinkedTransferQueue

In Java, the TransferQueue interface is a concurrent BlockingQueue implementation with support to support “synchronous message passing” between producers and consumers. The key feature of TransferQueue is the transfer() method that blocks until the message is handed off to a consumer. 1. TransferQueue Interface The TransferQueue is an interface in …

Java ArrayBlockingQueue class

ArrayBlockingQueue class is Java concurrent and bounded blocking queue implementation backed by an array. It orders elements FIFO (first-in-first-out). The head of the ArrayBlockingQueue is that element that has been on the queue the longest time. The tail of the ArrayBlockingQueue is that element that has been on the queue …

Java PriorityBlockingQueue class

Java PriorityBlockingQueue class is concurrent blocking queue data structure implementation in which objects are processed based on their priority. The “blocking” part of the name is added to imply the thread will block waiting until there’s an item available on the queue.

Java Priority Queue (+ Comparator Example)

Java PriorityQueue is an unbounded Queue implementation that processes the items based on priorities. Custom ordering can be enforced with a Comparator.

Java Spliterator (with Examples)

Unlike traditional iterators, Spliterator is designed with parallelism in mind and mainly helps in parallel processing when the collection or stream has a large number of elements.

Java ListIterator (with Examples)

The Java ListIterator interface is a bidirectional iterator that iterates over the elements in both forward and backward directions.

Guide to Java Iterator

Java Iterator interface is used to iterate over the elements of a Collection (List, Set or Map). The Iterator helps in retrieving the elements from the specified collection one by one and optionally performs operations over each element. Java Iterator was first introduced in Java 1.2 as a replacement of Enumerations. …

Java Comparator Interface

Java Comparator interface used to sort a array or list of objects based on custom order. Custom ordering of elements is imposed by implementing Comparator.compare() method in the objects.

Java Comparable Interface

Java Comparable interface is part of Collection Framework. Learn the purpose of Comparable interface and use it in different scenarios. 1. Comparable Interface 1.1. Why Implement Comparable? In Java, if we want to sort a List of elements then we can Collections.sort() method. It sorts the list items according to …

Java LinkedList class

Java LinkedList class is doubly-linked list implementation of the List and Deque interfaces. It implements all optional list operations, and permits all elements (including null). Table of Contents 1. LinkedList Hierarchy 2. LinkedList Features 3. LinkedList Constructors 4. LinkedList Methods 5. LinkedList Example 6. LinkedList Usecases 7. LinkedList Performance 8. …

Java TreeSet class

Java TreeSet class extends AbstractSet and implements NavigableSet interface. It is very similar to HashSet class, except it stores the element in sorted order.

Java LinkedHashSet class

Java LinkedHashSet class extends HashSet and implements Set interface. It is very very similar to HashSet class, except if offers the predictable iteration order.

Java HashSet class

Java HashSet class implements the Set interface, backed by a hash table(actually a HashMap instance). If does not offer any guarantees as to the iteration order, and allows null element.

Java Hashtable class

Java Hashtable class is an implementation of hash table data structure. It is very much similar to HashMap but it is synchronized while HashMap is not.

Java TreeMap class

Java TreeMap class stores key-value pairs very similar to the HashMap class. The difference is that TreeMap provides an efficient way to store key/value pairs in sorted order. The TreeMap class is a red-black tree-based NavigableMap implementation. This Java TreeMap tutorial will teach us about TreeMap class, methods, usecases, and …

Java LinkedHashMap class

LinkedHashMap in Java is used to store key-value pairs very similar to HashMap class. Difference is that LinkedHashMap maintains the order of elements inserted into it while HashMap is unordered. In this Java collection tutorial, we will learn about LinkedHashMap class, it’s methods, usecases and other important details. Table of …

Gson – Serialize and Deserialize a Map

Learn to serialize HashMap using Google Gson library. Also, learn to deserialize JSON string to HashMap containing custom Objects using Gson such that field values are copied into appropriate generic types. These conversions can be used to create deep cloning of the HashMap. 1. Maven Include the latest version of …

Clone a HashMap – Shallow and Deep Copy

Learn to create clone of a HashMap in Java. We will see the java programs to create shallow copy and deep copy of a HashMap. 1. Creating a Shallow Copy of Map We can create a shallow copy of a given HashMap in two ways. The first uses the clone() …

Remove Duplicates from a List or ArrayList in Java

Learn to remove duplicate elements from an ArrayList using different techniques such as HashSet, LinkedHashSet, and using Java 8 stream.

Java – Find, Count and Remove Duplicate Elements from Array

Learn to find, count and remove duplicate elements from an array in Java using Streams, Map and Set from the Collections framework.

Java ConcurrentHashMap vs Collections.synchronizedMap()

Java HashMap is not synchronized by default. Learn to use synchronized maps using Collections.synchronizedMap() and ConcurrentHashMap.

How to Join or Merge Two Maps in Java

Learn merging two hashmaps in both cases – ignoring duplicate keys (overwrites the value) or handling duplicate keys. 1. Merge Two HashMaps Ignoring Duplicate Keys This one is a simple solution. Use firstMap.putAll(secondMap) method that copies all of the mappings from the secondMap to firstMap. As we know hashmap does …

How to Compare Two Maps in Java

Learn to compare two Java Maps for the equality of their entries, key and values, and find the Map differences using Guava’s MapDifference API.

Basic Auth with Spring RestTemplate

Learn to add basic authentication to http requests invoked by Spring RestTemplate while accessing rest apis over the network. 1. Maven dependencies To work with Spring RestTemplate and HttpClient API, we must include spring-boot-starter-web and httpclient dependencies in pom.xml file. In this RestTemplate basic authentication tutorial, we are using dependencies. …

Securing Spring Boot REST API with Basic Auth

Learn to use basic authentication to secure the REST APIs created in a Spring boot application. The secured API will ask for user authentication credentials before giving access to the API response. 1. Maven Dependency The simplest way to add all required jars is to add the latest version of …

Java ArrayList spliterator() Example

Since Java 8, Spliterators are a special type of iterator that supports parallel iteration of portions of the source such as list, set, or array.

ArrayList removeIf(): Remove Elements Matching a Condition

Java ArrayList.removeIf() removes all elements that satisfy a condition by iterating through the elements and matching against the specified Predicate.

Java ArrayList replaceAll()

ArrayList replaceAll() transform each element in the list by applying a lambda expression or UnaryOperator implementation.

Java List retainAll()

In Java, the ArrayList.retainAll() retains only those elements in this list that are contained in the specified collection. Rest all elements are removed from the list. This method is exactly the opposite to removeAll() method. 1. Syntax The syntax to use the retainAll() method is: Method Argument – a collection …

Java ArrayList removeAll(): Remove All Occurrences of Element

ArrayList removeAll() removes all of matching elements that are contained in the specified method argument collection. It removes all occurrences of matching elements, not only first occurrence.

Java ArrayList remove(): Remove a Single Element from List

ArrayList remove() removes the first occurrence of the specified element from this list, if it is present, else the list remains unchanged.

Java ArrayList.listIterator()

Java ArrayList.listIterator() returns a bi-directional list iterator that iterates over the elements of the current list.

Java ArrayList forEach()

ArrayList forEach() method iterate the list and performs the argument action for each element of the list until all elements have been processed.

Java ArrayList clone() and Deep Copy Example

ArrayList.clone() creates a shallow copy of the given ArrayList. Learn to create deep copy and shallow copy of an arraylist with examples.

Java ArrayList.addAll() – Add Multiple Items to a List

Java ArrayList.addAll() appends all of the elements of argument collection to the list at the end or the specified index position.

Configure Timeouts with Spring RestTemplate

In this Spring boot2 RestTemplate timeout example, learn to configure connection timeout and read timeout in Spring RestTemplate with example. 1. Default Timeout By default, RestTemplate uses SimpleClientHttpRequestFactory which depends on the default configuration of HttpURLConnection. Look inside the class source, and you will find this. By default, RestTemplate uses …

Spring Boot RestTemplate POST Example

Learn to use Spring Boot RestTemplate for sending POST requests with JSON body, and HTTP headers including basic auth details.

Spring Boot RestTemplate GET Example

In this, Spring Boot RestTemplate GET request example, learn to use RestTemplate to invoke HTTP GET API and verify the response status code and the response entity body. To create the rest APIs, use the sourcecode provided in spring boot rest api example. 1. Setup Start with including the latest …

Testing POST APIs using Spring Boot TestRestTemplate

Learn to consume HTTP POST REST API with Spring TestRestTemplate. In this post request test example, we will be sending request body along with request headers. 1. Maven dependencies Make sure, you have spring-boot-starter-test dependency in your project to get access to TestRestTemplate class in runtime. If you are using …

Writing a POST REST API in Spring Boot

In Spring Boot 3 REST POST API tutorial, create an HTTP POST REST API, return the API response and add validations for the request body.

Java ArrayList add() – Add a Single Element to List

The ArrayList.add() in Java adds a single element to the list, either at the end of the list or at the specified index position. Always use generics for compile-time type safety while adding the element to the arraylist. 1. ArrayList.add() Method The add() method first ensures that there is sufficient …

Difference between LinkedList vs. ArrayList in Java

Java LinkedList and ArrayList are different in many aspects, and we need to understand both to decide when to use which class.

Java Vector vs ArrayList

In Java, ArrayList and Vector, both implement java.util.List interface and provide the capability to store and get objects within using simple API methods. Still, they are different in many aspects, and we need to understand both classes in detail to make a wise decision about when to use which class. …

Convert Set to List in Java and Vice-versa

Learn to convert a Set to List in Java using constructor, addAll() and Java 8 streams. Learn to convert list to set to remove duplicates.

Convert an Array to Mutable, Immutable and Unmodifiable Lists

Learn different and useful ways to convert array to list in Java. Learn to use Java 9 List, Java 8 Stream, Collections and Guava library.

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