Java List in Short

A List in Java is an ordered collection or sequence of elements that allows duplicates. It is part of the Java Collections Framework and is implemented by several classes such as ArrayList, LinkedList, and Vector. JDK 8, on the other hand, refers to Java Development Kit version 8, which introduced several new features and improvements to the Java programming language. This article aims to provide a simple explanation of Lists in Java and the new features introduced in JDK 8, within a limit of 2000 words.

1. Introduction to Lists in Java:
A List in Java is an interface that extends the Collection interface. It represents an ordered collection of elements, where each element is assigned an index based on its position in the list. Unlike arrays, Lists can dynamically grow and shrink in size as elements are added or removed. Some important characteristics of Lists include:

a. Ordered: Elements in a List are ordered and maintain the insertion order. Therefore, the position of an element in the List can be determined by its index.

b. Duplicates Allowed: Lists can contain duplicate elements. It means that the same element can appear multiple times in a List.

c. Dynamic Size: Lists can dynamically grow or shrink in size. Elements can be added or removed from any position within the List.

d. Random Access: Lists provide random access to elements based on their index. It means that we can directly access any element in a List using its index, unlike other collections like LinkedList.

2. Common List Implementations in Java:
The Java Collections Framework provides several classes that implement the List interface. Each implementation has its own advantages and is suitable for different use cases. The most commonly used List implementations in Java are:

a. ArrayList: ArrayList is one of the most widely used List implementations. It uses a dynamic array to store elements and provides fast random access. However, insertion and deletion operations at arbitrary positions take linear time, as the elements need to be shifted accordingly.

b. LinkedList: LinkedList is another popular List implementation. It uses a doubly-linked list to store elements. Insertion and deletion at arbitrary positions are faster compared to ArrayList, as no shifting of elements is required. However, random access to elements is slower as it needs to traverse the list from the beginning.

c. Vector: Vector is similar to ArrayList but provides synchronization, making it thread-safe. It is less commonly used due to its synchronized nature, which impacts performance. However, it can be useful in multi-threaded environments where thread-safety is a concern.

3. Creating and Manipulating Lists in Java:
To create a List in Java, you can use the ArrayList class as follows:

“`java
List list = new ArrayList();
“`

This creates an empty ArrayList of Strings. You can also initialize the List with some elements using the `Arrays.asList()` method:

“`java
List numbers = new ArrayList(Arrays.asList(1, 2, 3, 4, 5));
“`

Once the List is created, you can perform various operations on it, such as:

a. Adding Elements:

“`java
list.add(“Apple”);
list.add(“Banana”);
“`

This adds elements to the end of the List.

b. Accessing Elements:

“`java
String firstElement = list.get(0);
“`

This retrieves the element at the specified index.

c. Updating Elements:

“`java
list.set(1, “Orange”);
“`

This replaces the element at the specified index with a new element.

d. Removing Elements:

“`java
list.remove(“Apple”);
“`

This removes the specified element from the List.

e. Iterating over Elements:

“`java
for (String element : list) {
System.out.println(element);
}
“`

This iterates over each element in the List and performs some operation.

4. Introduction to JDK 8 Features:
JDK 8 introduced several new features and enhancements to the Java programming language. Some of the major features include:

a. Lambda Expressions: Lambda expressions allow the representation of anonymous functions as objects. They enable functional programming by providing a concise syntax for writing functions and passing them as arguments to methods.

b. Stream API: The Stream API provides a new way of processing collections of objects. It allows performing various operations on collections, such as filtering, mapping, reducing, and more, in a declarative and parallelizable manner.

c. Default Methods: Default methods enable adding new methods to existing interfaces without breaking the compatibility with implementing classes. It allows adding additional functionality to interfaces without forcing all implementing classes to implement the new methods.

d. Method References: Method references provide a way to refer to methods or constructors of functional interfaces directly. They make the code more readable and concise by reducing the amount of boilerplate code.

e. Optional Class: The Optional class provides a container object that may or may not contain a non-null value. It helps in avoiding null pointer exceptions and makes the code more robust.

f. Date and Time API: JDK 8 introduced a new Date and Time API that provides better support for date and time manipulation. It addresses the limitations of the old java.util.Date and java.util.Calendar classes and offers a more intuitive and thread-safe API.

5. Using JDK 8 Features with Lists:
JDK 8 features can be combined with Lists to write more concise and expressive code. Let’s see how some of these features can be used with Lists:

a. Lambda Expressions and Stream API:

“`java
List fruits = Arrays.asList(“Apple”, “Banana”, “Orange”, “Mango”);

List filteredFruits = fruits.stream()
.filter(fruit -> fruit.startsWith(“A”))
.collect(Collectors.toList());
“`

This code uses lambda expressions and the Stream API to filter the fruits starting with “A” and collect them into a new List.

b. Method References:

“`java
List numbers = Arrays.asList(1, 2, 3, 4, 5);

numbers.forEach(System.out::println);
“`

This code uses method references to print each number in the List.

c. Optional Class:

“`java
List fruits = Arrays.asList(“Apple”, “Banana”, “Orange”, “Mango”);

Optional firstFruit = fruits.stream()
.findFirst();

if (firstFruit.isPresent()) {
System.out.println(firstFruit.get());
} else {
System.out.println(“No fruits found.”);
}
“`

This code uses the Optional class to handle the case where no fruits are found in the List.

6. Conclusion:
In this article, we discussed Lists in Java and the new features introduced in JDK 8. Lists provide an ordered collection of elements with various operations for manipulation. JDK 8 introduced features like lambda expressions, the Stream API, default methods, and more, which can be combined with Lists to write more expressive and concise code. Understanding Lists and JDK 8 features is essential for Java developers to leverage the full potential of the language and write efficient and maintainable code.