Java Array To Arraylist: Java Explained

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Java is a highly popular and preferred programming language used by millions of developers around the world. It is one of the most versatile and secure programming languages that is used to create a variety of programs and applications. One of the commonly used features in Java is the array and arraylist. In this article, we will look into the concept of a Java array and arraylist, explain how to convert from an array to an arraylist, and also provide some essential tips and examples on how to perform the conversion.

What is an Array in Java?

An array is a data structure which is used to store information within a certain ‘index’ range, that are commonly referred to as elements. Arrays are declared with a unique data type which define the type of elements which can be stored within the array. Each element in an array has its own unique index which can be used to refer to it when needed. In Java, an array is declared with a fixed-size which cannot be altered once it has been created unless it is recreated. Arrays are often used when dealing with multiple items of data with similar properties as they can store a lot of information within a single array.

Arrays are also useful for sorting data, as they can be sorted in ascending or descending order depending on the type of data stored. Additionally, arrays can be used to store objects, which can be accessed and manipulated using the array index. Arrays are a powerful tool for organizing and manipulating data, and are used extensively in Java programming.

What is an ArrayList in Java?

An ArrayList is a dynamic data structure which differs from an array in that its size can be modified over its lifetime. An arraylist is created with no fixed number of elements which allows the programmer to easily add or remove elements as needed. This makes an arraylist a more flexible version of an array and allows for easy modification as it does not need to be recreated if a certain element needs to be added or removed. The main benefit of an arraylist over an array is that it provides greater flexibility when managing elements.

ArrayLists are also more efficient than arrays when it comes to memory usage. Since an arraylist can be resized as needed, it does not need to allocate a large amount of memory upfront. This makes it a more efficient data structure for managing large amounts of data. Additionally, arraylists are also more efficient when it comes to searching for elements as they can be accessed in constant time.

Converting from an Array to an ArrayList

As an array and arraylist serve similar purposes but possess different characteristics, there may be situations where it is beneficial to convert an array into an arraylist. This process is made easy by Java’s Collection class which provides the “newArrayList()” method which can be used to convert an array into an arraylist with minimal effort; it simply requires specifying the array as an argument and setting the newly created arraylist to its own variable. This method is ideal for converting single dimension arrays as it allows for precise control over which elements to transfer while also avoiding any potential discrepancies between the two structures such as overflow.

When converting an array to an arraylist, it is important to note that the arraylist will be a shallow copy of the original array. This means that any changes made to the arraylist will also be reflected in the original array. Additionally, the arraylist will not be able to store primitive data types such as ints and doubles, so these must be converted to their corresponding wrapper classes before being added to the arraylist.

Benefits of Converting from Array to ArrayList

The main benefit of converting from an array to an arraylist lies within its dynamic nature; as an arraylist does not have a fixed-size, it allows for more flexibility when adding new elements or removing existing ones without having to recreate the arraylist; something which would need to be done with arrays in order to facilitate any kind of alteration. This makes converting from an array to an arraylist beneficial if a development project requires frequent alterations or if the size of the data set needs to remain fluid.

In addition, arraylists are more efficient when it comes to memory usage. As the size of an arraylist can be adjusted dynamically, it does not require the same amount of memory as an array, which needs to be allocated a fixed amount of memory when it is created. This makes arraylists a more efficient choice when dealing with large data sets.

Potential Drawbacks of Converting from Array to ArrayList

In comparison to arrays, arraylists occupy more memory space than arrays; Therefore, if a large quantity of elements needs to be stored within large scale development projects, using an array over a list could prove more efficient in terms of memory usage. Additionally, the conversion process from one element to the other requires certain parameters set by the programmer which need to be adjusted depending on the type of elements being stored; if these appear disproportionate, this could lead to discrepancies in both the data and memory usage.

Furthermore, the conversion process from array to arraylist can be time consuming and complex, as the programmer must ensure that all elements are correctly converted and stored in the new data structure. This can be especially difficult if the array contains a large number of elements, as the programmer must manually check each element to ensure that it has been correctly converted. Additionally, the programmer must also ensure that the arraylist is correctly configured to store the elements, as any errors in this process could lead to data loss or corruption.

Essential Tips on How to Convert an Array To An ArrayList

  • Make sure that you are aware of the type of elements which will be stored in your array by researching what type it is and setting any required specifications.
  • Be mindful of memory usage when converting; if feasible, try to choose the most efficient structure given the requirements of your project.
  • Ensure that you have set up all parameters correctly when constructing your arraylist; any discrepancies here could cause wrong or corrupted data.

Examples of Converting an Array To An ArrayList

Let’s take a look at how you can use Java’s Collection class in order to convert from an array to an arraylist. Suppose we have an integer array called “myIntArray” which contains the values 1, 2, 3 and 4. In order to convert this array into an ArrayList, we first need to set up a variable for our newly created ArrayList:

ArrayList<Integer> myIntList = new ArrayList<>(); 

Once declared, we can then use Java’s “newArrayList()” method in order to convert our array into an ArrayList:

myIntList = Ints.newArrayList(myIntArray); 

This will copy all the contents within our “myIntArray” into our newly created “myIntList” and convert it into an ArrayList.


Arrays and ArrayLists are important concepts in Java which are both utilized when dealing with larger quantities of data with similar properties. While both structures serve similar purposes and are mostly interchangeable, they possess clear differences which may favor one over the other depending on the requirements of a certain project. When dealing with projects that require frequent edits or changes, converting from a fixed-size array into an ArrayList may be beneficial due to the dynamic nature that it provides. Additionally, this process can be made easy by simply making use of Java’s Collection class which provides convenient methods for conversion between the two structures.

Anand Das

Anand Das

Anand is Co-founder and CTO of Bito. He leads technical strategy and engineering, and is our biggest user! Formerly, Anand was CTO of Eyeota, a data company acquired by Dun & Bradstreet. He is co-founder of PubMatic, where he led the building of an ad exchange system that handles over 1 Trillion bids per day.

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