10 Examples of Stream API in Java 8 - count + filter + map + distinct + collect() Examples

The Java 8 release of Java Programming language was a game-changer version. It not only provided some useful methods but totally changed the way you write programs in Java. The most significant change it brings in the mindset of Java developers was to think functional and supported that by providing critical features like lambda expression and Stream API, which takes advantage of parallel processing and functional operations like filter, map, flatMap, etc. Since then, a lot of Java developers are trying their hands to learn those significant changes like lambda expression, method reference, new Date and Time classes, and, more importantly, Stream API for bulk data operations.

How to debug Java 8 Stream Pipeline - peek() method Example Tutorial

Hello guys, I have been writing about some important methods from Java SE 8  like map(), flatMap(), collect(), etc for quite some time, and today I'll share my experience with another useful method peek() from java.utill.stream.Stream class. The peek() method of the Stream class can be very useful to debug and understand streams in Java 8. You can use the peek() method to see the elements as they flow from one step to another like when you use the filter() method for filtering, you can actually see how filtering is working like lazy evaluation as well as which elements are filtered.

How to convert ArrayList to HashMap and LinkedHashMap in Java 8 - Example Tutorial

One of the common tasks in Java is to convert a List of objects, like a List<T> into a Map, I mean Map<K, V>, where K is some property of the object and V is the actual object. For example, suppose you have a List<Order>, and you want to convert it into a Map, e.g. Map<OrderId, Order>, how do you that? Well, the simplest way to achieve this is iterating over List and add each element to the Map by extracting keys and using the actual element as an object. This is exactly what many of us do in the pre-Java 8 world, but JDK 8 has made it even simpler.

Java 8 Stream map() function Example with Explanation

The map is a well-known functional programming concept that is incorporated into Java 8. Map is a function defined in java.util.stream.Streams class, which is used to transform each element of the stream by applying a function to each element. Because of this property, you can use a map() in Java 8 to transform a Collection, List, Set, or Map. For example, if you have a list of String and you want to convert all of them into upper case, how will you do this? Prior to Java 8, there is no function to do this. 

How to Convert a Comma Separated String to an ArrayList in Java - Example Tutorial

Suppose you have a comma-separated list of String e.g. "Samsung, Apple, Sony, Google, Microsoft, Amazon" and you want to convert it into an ArrayList containing all String elements e.g. Samsung, Apple, Google, etc. How do you do that? Well, Java doesn't provide any such constructor or factory method to create ArrayList from delimited String, but you can use String.split() method and Arrays.asList() method together to create an ArrayList from any delimited String, not just comma separated one. 

How to create and initialize List or ArrayList in one line in Java? Example

creating and initializing List at the same time

Sometimes we want to create and initialize a List like ArrayList or LinkedList in one line much like creating an array and initializing it on the same line. If you look at The array on Java programming language you can create and initialize both primitive and object arrays e.g. String array very easily in just one line but in order to create a List equivalent of that array, you need to type a lot of code. This is also one of the tricky Java question sometimes appears in Interview as Write Java code to create and initialize ArrayList in the same line.

How to Order and Sort Objects in Java? Comparator and Comparable Example

Java Object Sorting Example

How do you sort a list of Objects in Java is one of the frequently asked coding questions in Java interviews and surprisingly not every Java programmers know How sorting of object happens in Java. Comparator and Comparable interface along with Collections.sort() method are used to sort the list of objects in Java. compare() and compareTo() method of Comparator and Comparable interface provides comparison logic needed for sorting objects. compareTo() method is used to provide Object's natural order sorting and compare() method is used to sort Object with any arbitrary field. 

ArrayList vs Vector in Java? Interview Question Answer

ArrayList vs Vector in Java
ArrayList and Vector are the two most widely used Collection classes in Java and are used to store objects in an ordered fashion. Every Java programmer which is introduced to Java Collection Framework either started with Vector or ArrayList. For beginners Difference between Vector and ArrayList in Java and LinkedList vs ArrayList are the two most popular Java Interview questions. ArrayList vs Vector is not only important from an interview perspective but also on the effective use of Java Collection API. 

How to Search an Element in Java Array with Example? ArrayUtils Tutorial

find an index of the object in Array

While programming in Java, many times we need to check if a String array contains a particular String or an integer array contains a number or not. Though array is an object in Java but it does not provide any convenient method to perform searching elements or finding elements. Sometimes you even need an index of an item stored in Array, unfortunately, Java API does not provide any direct method. Thanks to Open Source Apache Commons provides a utility class called ArrayUtils which allows you to check for an Item in Array, find its index in the array, find its lastIndex in Array and perform several other common operations. 

How to use Deque Data Structure in Java? Example Tutorial

Hello friends, I am really glad to see you all again here. And I know you are here to learn new and valuable Java concepts and continue your journey on Java. Today we are gonna learn something that is really important logically. yes! you heard right, we are going to learn about Deque data structure in Java and how to use Deque in the Java program. Deque is a special data structure, a double-ended queue that allows you to process elements at both ends, I mean you can add and remove objects from both front and rear end. It's a short form of Double-Ended Queue and pronounced as "Deck".  

Java ArrayList Tutorials and Examples for Beginners (with Java ArrayList Cheat Sheet)

Hello guys, if you want to learn ArrayList in-depth and looking for a complete guide on ArrayList then you have come to the right place. Earlier, I have shared the best Java collection courses and in this article, I am going to share tutorials and examples to learn and master ArrayList in Java. In the last 10 years, I have written several ArrayList tutorials, touching different ArrayList concepts and many how-to-do examples with ArrayList. In this tutorial, I am giving a summary of each of them. Why? So that any Java beginner who wants to learn ArrayList in detail, can go through the relevant tutorial and learn.

10 Examples of Comparator, Comparable, and Sorting in Java 8

Hello guys, the Comparator class is used to provide code or logic for comparing objects in Java, while sorting a list of objects or a collection of objects. It's close cousin of Comparable which provides natural order sorting e.g. ascending and descending orders for numbers like int, short, long or float, and lexicographic order for String i.e. the order on which words are arranged in dictionaries. The Comparators are used while sorting arrays, lists and collections. You pass logic to compare objects and sorting methods like Collections.sort() use that logic to compare elements until they are arranged in sorted order. 

How to shuffle a List in Java? Collections.shuffle() Example

Hello guys, if you have a List of numbers and you want to shuff it but don't know how then you have come to the right place. Shuffling is an important technique which is used quite a lot on coding games like number guessing games and card games., The java.util.Collections class provides shuffle() method which can be used to randomize objects stored in a List in Java. Since List is an ordered collection and maintains the order on which objects are inserted into it, you may need to randomize elements if you need them in a different order. Collections.shuffle() method uses default randomness to randomize elements but you also have an overloaded version of shuffle() to provide an instance of the java.util.Random object, which can be used to randomize elements.

Difference between HashSet and HashMap in Java? Answered

HashSet and HashMap in Java
Hello friends, if you have given Java developer interview then there is good chance that you may have come across questions like Difference between HashSet vs HashMap or HashSet vs TreeSet etc. In this article, we are going to discuss differnece between HashMap and HashSet, two of the popular Collection classes from JDK. The HashSet vs HashMap is a classical Java Collection interview question that focuses on What are differences between HashSet and HashMap in terms of features, usage, and performance. If you are in Java programming even for a year or so, you are likely to be familiar with What is HashSet in Java and What is HashMap in Java, these two are the most popular collection classes. 

How to sort ArrayList in Java? Examples

Hello Java programmers, sorting ArrayList in Java is not difficult; there are multiple ways to sort a given ArrayList in Java. For example you can use  the Collections.sort() method to  sort ArrayList in ascending and descending order in Java. The  Collections.sort() the method optionally accepts a Comparator. If provided, it uses Comparators' compare() method to compare Objects stored in Collection to compare with each other; in case of no explicit Comparator, Comparable interfaces' compareTo() method is used to compare objects from each other. If objects stored in ArrayList don't implement Comparable, they can not be sorted using the Collections.sort() the method in Java.

How to replace an element of ArrayList in Java? Example

You can use the set() method of java.util.ArrayList class to replace an existing element of ArrayList in Java. The set(int index, E element) method takes two parameters, the first is the index of an element you want to replace, and the second is the new value you want to insert. You can use this method as long as your ArrayList is not immutable, I mean,  not created using the Collections.unmodifiableList(), in such case the set() method throws java.lang.UnsupportedOperationExcepiton. 

Difference between ArrayList and HashSet in Java? Answer with Example

ArrayList vs HashSet Java

The main difference between ArrayList and HashSet is that one is a List implementation while the other is a Set implementation. It means all the differences between a List data structure and a Set data structure also apply to this pair. For example, List implementations are ordered, it stores the element in the order they were added, while Set implementation doesn't provide such a guarantee. Similarly, since List provides Random access, you can access any element directly if you know the index, but Set doesn't provide such a facility. 

Difference between Queue and Deque in Java? Example Tutorial

Hello guys, today I am going to share another interesting question from Java interview, what is difference between Queue and Deque in Java. This question was asked to one of my reader in a recent interview with JP Morgan Mumbai and this is also a popular Java collection interview question. While he was able to answer the question, he wasn't able to convince interviewer so he asked me how to answer this question. So I am writing this post to share my answer on Queue vs Deque in Java. In the vast world of Java programming, the need to manage data efficiently often leads developers to specialized data structures. 

How to find length/size of ArrayList in Java? Example

You can use the size() method of java.util.ArrayList to find the length or size of ArrayList in Java. The size() method returns an integer equal to a number of elements present in the array list. It's different than the length of the array which is backing the ArrayList, which is called the capacity of ArrayList. When you create an object of ArrayList in Java without specifying a capacity, it is created with a default capacity which is 10. Since ArrayList is a growable array, it automatically resizes when the size (number of elements in the array list) grows beyond a threshold. 

How to remove all elements of ArrayList in Java - RemoveAll Example

There are two ways to remove all elements of an ArrayList in Java, either by using clear() or by using the removeAll() method. Both methods are defined in the java.util.List and java.util.Collection interface, hence they are available not just to ArrayList but also to Vector or LinkedList, etc. Both elements remove all objects from ArrayList but there is a subtle difference in how they do. The clear() method is straightforward, it traverses through the ArrayList and sets all indices to null, which means the ArrayList becomes empty and all elements become eligible to Garbage collection, provided there are no more references to them.