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.

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.

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.

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. 

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.

10 Example of List in Java

Hello guys,  Java, as a versatile and widely used programming language, offers a plethora of data structures to developers. One of them is List which is also fundamental component in Java's collection framework, play a pivotal role in managing and manipulating sequences of elements. In the past, I have shared 10 Examples of HashMap in Java and In this article, we'll delve into Java lists, exploring their features and providing ten illustrative examples to deepen your understanding. List are also a popular topic from Java interviews with questions like difference between ArrayList and LinkedList which have been asked to me almost 10 times in past 20 years. 

How to Convert a List to a Set in Java with Example

How to convert a List to Set in Java

Many times we need to convert one collection to another like converting a List to a Set. It's also an easy way to copy contents from one collection to other in Java, like from List to Set or Set to List. Thanks to the Collection framework in Java, copying collections from one to another is extremely easy. Since every Collection class implements a Collection interface that defines the addAll() method, which can be used to create a collection from contents of another collection.

Difference between ArrayList and HashMap in Java

Difference between ArrayList and HashMap in Java
One of the most critical differences between the HashMap and ArrayList class is that the former is the implementation of the hash table while the latter is a dynamic array that can resize itself. The HashMap and ArrayList are two of the most popular classes from the Java Collection framework. Though both are used to store objects they are completely different in their implementation, working, and usage. The main difference between ArrayList and HashMap is that ArrayList is an index-based data structure backed by an array while HashMap is a map data structure that works on hashing to retrieve stored values. 

How to declare ArrayList with values in Java? Examples

Sometimes you want to create an ArrayList with values, just like you initialize t at the time of declaration, as shown below:

int[] primes = {2, 3, 5, 7, 11, 13, 17};
or
String[] names = {"john", "Johnny", "Tom", "Harry"};

but unfortunately, ArrayList doesn't support such kind of declaration in Java. But don't worry, there is a workaround to declare an ArrayList with values e.g. String, integers, floats, or doubles by using the Arrays.asList() method, which is nothing but a shortcut to convert an Array to ArrayList.

How to convert a List to Array in Java? Example Tutorial

There is no easy way to convert an array to a list in Java, but you can easily convert a list into an array by calling the toArray() method, which List inherits from the Collection interface. If you solely rely on core JDK, then the only way to convert an array to a list is by looping over the array and populating the list one element at a time. But if you can use open source libraries like Google Guava or Apache Commons lang then there are many utility classes to convert list to array and vice-versa, as shown in this tutorial. If you are working on a Java application, you will often need to convert between list and array. 

How to get first and last elements form ArrayList in Java

There are times when you need to get the first or last element of an ArrayList. One of the common scenarios where you need the first and last element of a list is supposed you have a sorted list and want to get the highest and lowest element? How do you get that? The first element is your lowest and the last element is your highest, provided ArrayList is sorted in ascending order. If it's opposite then the first element would be the maximum and the last element would be the minimum. This is quite easy to do in ArrayList because the first element is stored at index 0 and the last element is on index, size - 1. 

Difference between synchronized ArrayList and CopyOnWriteArrayList in Java?

What is the difference between a CopyOnWriteArrayList and a Synchronized ArrayList is one of the popular Java interview questions, particularly for beginners with 1 or 2 years of experienced programmers. Though both synchronized ArrayList and CopyOnWriteArrayList provide you thread-safety and you can use both of them when your list is shared between multiple threads, there is a subtle difference between them, Synchronized ArrayList is a synchronized collection while CopyOnWriteArrayList is a concurrent collection. What does this mean? It means is that CopyOnWriteArrayList is designed keeping concurrency in mind and it is more scalable than synchronized ArrayList if the list is primarily used for reading. 

Top 20 Java ArrayList Interview Questions and Answers

Hello guys, if you are preparing for Java interviews then you have come to the right place. In the past, I have shared 130+ Java interviews questions and online courses to prepare for Java interviews and In this article, I am going to share some of the good Java interview questions based upon the ArrayList class. I have hardly seen a Java interview without any question from ArrayList, and why not its one of the most popular collection class and every Java developer use it on their day to day work. Another reason for asking a question related to ArrayList is that you can ask a wide variety of questions to really check the breadth and depth of a candidate's knowledge.

How to Synchronize an ArrayList in Java with Example

ArrayList is a very useful Collection in Java, I guess most used one as well but it is not synchronized. What this mean? It means you cannot share an instance of ArrayList between multiple threads if they are not just reading from it but also writing or updating elements. So how can we synchronize ArrayList? Well, we'll come to that in a second but did you thought why ArrayList is not synchronized in the first place? Since multi-threading is a core strength of Java and almost all Java programs have more than one thread, why Java designer does not make it easy for ArrayList to be used in such an environment? 

How to reverse ArrayList in Java with Example

You can reverse ArrayList in Java by using the reverse() method of java.util.Collections class. This is one of the many utility methods provided by the Collections class e.g. sort() method for sorting ArrayList. The Collections.reverse() method also accepts a List, so you not only can reverse ArrayList but also any other implementation of List interface e.g. LinkedList or Vector or even a custom implementation. This method has a time complexity of O(n) i.e. it runs on linear time because it uses ListIterator of the given list.  It reverses the order of an element in the specified list. 

How to Remove Duplicates from ArrayList in Java [Example]

ArrayList is the most popular implementation of the List interface from Java's Collection framework, but it allows duplicates. Though there is another collection called Set which is primarily designed to store unique elements, there are situations when you receive a List like ArrayList in your code and you need to ensure that it doesn't contain any duplicate before processing. Since with ArrayList you cannot guarantee uniqueness, there is no other choice but to remove repeated elements from ArrayList. 

How to Sort a List into Ascending and Descending Order in Java? Examples

ArrayList, Set Sorting in Ascending – Descending Order Java

Sorting List, Set, and ArrayList in Java in ascending and descending order is very easy, You just need to know the correct API method to do that. For example Collections.sort()  method will sort the collection passed to it,  doesn't return anything just sort the collection itself. From Java 8 onwards you can also use List.sort() method to sort a List in ascending or descending order directly without using Collections.sort() method. If you like to use Stream API, it also provide a sort() method to sort elements inside Stream. You can also use that to sort any List. For example, you can first convert a List to Stream and then sort the Stream and collect the result into another List. 

How to convert List Of of Object to Map of Object (key, value) In Java? Example Tutorial

Hello guys, if you have a list of object and you want to conver into Map of object or key value pair then you can use different ways like looping over list and then adding values to map, or you can use Collectors.toMap() by using Stream API, You can even use flatMap() function if you want to convert list of one type of object to Map of another type of object. All this is possible and I will show you code example of how to do that in this article, But, before we get into the process of how you can convert a list of one object to another in Java, let me tell you a bit more about what Java really is. 

Java program to get SubList from ArrayList - Example

Sometimes we need subList from ArrayList in Java. For example, we have an ArrayList of 10 objects and we only need 5 objects or we need an object from index 2 to 6, these are called subList in Java. Java collection API provides a method to get SubList from ArrayList. In this Java tutorial, we will see an example of getting SubList from ArrayList in Java. In this program, we have an ArrayList which contains 4 String objects. Later we call ArrayList.subList() method to get part of that List.