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Arrays.aslist in Java

Hello. In this tutorial, we will make understand and implement java.util.Arrays.asList(…) method.

1. Introduction

Arrays.asList() method in java is used to create a fixed-size list in java. It is a static method that returns a list of homogeneous elements and does not throw any exceptions. The method is represented by the below syntax and below reports compilation errors if heterogeneous elements are passed.

Method syntax

public static <T> List<T> asList(T... a)

2. Practice

Let us dive into some practice stuff from here and I am assuming that you already have Java 1.8 or greater installed on your local machine. I am using JetBrains IntelliJ IDEA as my preferred IDE. You’re free to choose the IDE of your choice.

2.1 Creating an implementation class

Create a java file that will show the implementation of the asList(…) method. example1() and example2() will be responsible to show the usage of the asList(…) method via code snippets and example3() will throw UnsupportedOperationException if something unexpected happens.

Implementation class

package com.practice;

import java.util.Arrays;
import java.util.List;

// pojo class
class User {
	private int id;
	private String name;
	
	public User(int id, String name) {
		this.id = id;
		this.name = name;
	}
	
	public int getId() {
		return id;
	}
	
	public String getName() {
		return name;
	}
	
	@Override
	public String toString() {
		return "[id=" + id + ", name=" + name + "]";
	}
	
	public static List<User> createUsers() {
		return Arrays.asList(new User(101, "abc"), new User(102, "pqr"));
	}
}

// implementation class
public class ArraysAsListExample {

	// syntax - static <T> List<T> asList(T... a)
	
	private static void example1() {
		List<String> elements = Arrays.asList("apple", "banana", "kiwi", "mango");
		System.out.println(elements);
	}
	
	private static void example2() {
		List<User> users = User.createUsers();
		users.forEach(user -> System.out.println(user));
	}
	
	private static void example3() {
		List<User> users = User.createUsers();
		users.forEach(user -> System.out.println(user));
		
		// adding new element to the list
		// will throw java.lang.UnsupportedOperationException
		users.add(new User(103, "rst"));
	}
	
	// driver code
	public static void main(String[] args) {
		example1();
		System.out.println("\n");
		example2();
		System.out.println("\n");
		example3();
	}
}

3. Demo

Run the file as a java file and if everything goes well the following logs will be shown on the IDE console.

Fig. 1: Console output

That is all for this tutorial and I hope the article served you with whatever you were looking for. Happy Learning and do not forget to share!

4. Summary

In this tutorial, we discussed the practical implementation of Arrays.asList() method. You can download the source code from the Downloads section.

5. Download the Project

This was a tutorial to understand the Arrays.asList() method in java.

Download
You can download the full source code of this example here: Arrays.aslist in Java

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