How To Convert ArrayList To Array In Java?

Java is considered one of the most used programming languages globally, and it disposes a vast and diversified kit of utilities for articulating and processing data for application developers. ArrayList class is one among several types of utility which is found in Java’s java.util package. It offers a dynamic array that makes it convenient to add or perhaps delete components without being concerned by the dimensions of the selection, and for that reason, it is a beneficial tool for assortment manipulation.

In this blog post, we will focus on how to convert an ArrayList to array in Java, how we could approach this, and what one should, or should not do (sometimes referred to as the flaws) in Java. Let’s get started!

What Are ArrayList and Array in Java?

Before we jump into the conversion methods, let’s briefly understand what ArrayList and arrays are:

ArrayList

An ArrayList is a class in Java in the java.util package, and is an extension of the built-in array, which is resizable. It enables you to make additions or subtractions to it and offers method availability to clients in cases where elements are assembled.

Key Features:

• Dynamic resizing.
• They are ordered according to the order of insertion.
• Supplies type parameterization for the generic types for achieving type safety.
• Faster than arrays when it comes to adding and removing elements constantly slower than arrays for direct element access.

Array

Java array is an object that contains in fixed number of items of the same data type and it can be one-dimensional to multidimensional array. Arrays are easy to use and fast, however, they are not as versatile as an ArrayList .

Key Features:

• Fixed size.
• Compelling to become highly performant for element access.
• We do not have overloaded utility methods like existent in the ArrayList.

Why Convert ArrayList to Array?

There are several reasons why developers may need to convert an ArrayList to an array:

1. Legacy Code: There are many older Java APIs that only support arrays almost in their function signatures.
2. Performance: But arrays are better in terms of performance.
3. Fixed Size Requirement: Arrays are not dynamism in their nature since once created you cannot change their size and so are good for those occasions whereby the count of items that you intend to store in the collection is fixed.
4. Integration: Most libraries or systems might need the data in an array form.

Methods to Convert ArrayList to Array in Java

Java offers many ways to execute this kind of conversion, which has its strengths to weaknesses. Now let me expand on these methods.

1. Using the toArray() Method Without Parameters

One of the most straightforward ways of converting an ArrayList to an array is by the use of the toArray() method, (specifically with no argument).

import java.util.ArrayList;

public class ArrayListToArrayExample {
    public static void main(String[] args) {
        ArrayList<String> list = new ArrayList<>();
        list.add("Apple");
        list.add("Banana");
        list.add("Cherry");

        // Convert ArrayList to Array
        Object[] array = list.toArray();

        // Print Array
        for (Object obj : array) {
            System.out.println(obj);
        }
    }
}

Output:
Apple
Banana
Cherry

Key Points:

• Returns an Object[] array.
• If you need a certain data type, such as a String array, you can only do the typecasting.

Drawbacks:

• Lack of type safety.
• There is a need for extra type casting.

2. Using the toArray(T[] a) Method

Another safer and faster way of converting ArrayList to array is by using the overloaded toArray() method which takes an array of a specific type.

import java.util.ArrayList;

public class ArrayListToArrayExample {
    public static void main(String[] args) {
        ArrayList<String> list = new ArrayList<>();
        list.add("Apple");
        list.add("Banana");
        list.add("Cherry");

        // Convert ArrayList to Array
        String[] array = list.toArray(new String[0]);

        // Print Array
        for (String s : array) {
            System.out.println(s);
        }
    }
}

Output:
Apple
Banana
Cherry

Key Points:

• The type of the returned array will depend on the type of the array passed as an argument.
• If the total length of the array is big enough it becomes the destination otherwise a new array is created for it.

Advantages:

• Type-safe.
• Avoids typecasting.

3. Using Java Streams

The Stream API appeared with Java 8, and it embodied the more efficient and functional way to deal with data. Let's use Stream API to know how to convert an ArrayList into an array.

import java.util.ArrayList;
import java.util.stream.Collectors;

public class ArrayListToArrayExample {
    public static void main(String[] args) {
        ArrayList<String> list = new ArrayList<>();
        list.add("Apple");
        list.add("Banana");
        list.add("Cherry");

        // Convert ArrayList to Array
        String[] array = list.stream().toArray(String[]::new);

        // Print Array
        for (String s : array) {
            System.out.println(s);
        }
    }
}

Output:
Apple
Banana
Cherry

Key Points:

• Uses toArray() With the help of a Generator function.
• Uses functional programming as one of its factors.

Advantages:

• Concise and modern syntax.
• The library is very compatible with Java’s functional programming model.

4. Using a Loop

For developers who already know and want to use the conventional way to implement for loop or enhanced for loop to copy elements from the ArrayList to the array.

Example:

import java.util.ArrayList;

public class ArrayListToArrayExample {
    public static void main(String[] args) {
        ArrayList<String> list = new ArrayList<>();
        list.add("Apple");
        list.add("Banana");
        list.add("Cherry");

        // Convert ArrayList to Array
        String[] array = new String[list.size()];
        for (int i = 0; i < list.size(); i++) {
            array[i] = list.get(i);
        }

        // Print Array
        for (String s : array) {
            System.out.println(s);
        }
    }
}

Output:
Apple
Banana
Cherry

Advantages:

• Total freedom in the actual conversion exercise.
• It is helpful in situations where some sort of further processing is achieved while reconstructing the data.

Comparison of Methods

Conclusion

Converting ArrayList to Array in Java is one of the most frequent operations in Java programming, so, it is important to discuss the possible ways with this aim. No matter whether you are interested in basic techniques, want to get the best performance, or prefer the most recent approaches within the programming paradigms, JDK 7 offers the method to satisfy your requirements.

Remembering the problems discussed in this article, and using these tips, you will be able to create both high-speed and reliable code. Happy coding!