Array Vs ArrayList in Java [In-Depth Tutorial]


Bashir Alam

JAVA

When working with Java programming, selecting the right data structure is crucial for building efficient and well-organized applications. Two such data structures, arrays and ArrayLists, often become the center of discussion in the context of "Array vs ArrayList" comparisons. In this article, we will dive deep into the nuances of these two data structures, examining their differences, use cases, and performance trade-offs. Whether you are an experienced Java developer or a programming novice, this comprehensive analysis of "Array vs ArrayList" in Java will equip you with the knowledge needed to make informed decisions when choosing the appropriate data structure for your projects. So, let's embark on this journey to explore the key distinctions between these vital components in a Java programmer's toolkit.

 

Arrays in Java

In Java, an array is a collection of elements of the same data type. Once an array is created, its size cannot be changed. Arrays are useful when you know the size of the collection you need to store and when you need fast access to its elements.

 

Declaring Arrays in Java

To declare an array in Java, you need to specify the data type of the elements that the array will store, followed by the name of the array and the number of elements it will store. The syntax for declaring an array is as follows:

datatype[] arrayName = new datatype[size];

Here, datatype is the type of data that the array will store, arrayName is the name you choose for the array, and size is the number of elements the array can hold.

For example, to declare an integer array named myArray that can hold 5 elements, you can use the following code:

int[] myArray = new int[5];

 

Initializing Arrays

After declaring an array, you can initialize its elements by assigning values to them. You can initialize the array elements individually or use a loop. Here's an example of initializing an integer array named myArray:

myArray[0] = 10;
myArray[1] = 20;
myArray[2] = 30;
myArray[3] = 40;
myArray[4] = 50;

Alternatively, you can initialize the array elements using a loop. Here's an example of initializing an integer array named myArray using a for loop:

for (int i = 0; i < myArray.length; i++) {
    myArray[i] = i * 10;
}

This loop initializes the elements of the myArray array with values 0, 10, 20, 30, 40.

 

Accessing Array Elements

To access an element of an array, you can use its index value. The index of an array starts at 0 and ends at length-1, where length is the number of elements in the array. Here's an example of accessing an element of an integer array named myArray:

int element = myArray[2];

This statement assigns the value 30 to the element variable, which corresponds to the third element of the myArray array.

 

Multidimensional Arrays

In Java, you can also create multidimensional arrays, which are arrays of arrays. Multidimensional arrays can be declared and initialized in the same way as one-dimensional arrays. Here's an example of declaring a 2-dimensional integer array named myArray:

int[][] myArray = new int[3][4];

This code creates a 2-dimensional array that can hold 3 rows and 4 columns of integers. To initialize the elements of a multidimensional array, you need to use nested loops. Here's an example of initializing a 2-dimensional integer array named myArray:

for (int i = 0; i < myArray.length; i++) {
    for (int j = 0; j < myArray[i].length; j++) {
        myArray[i][j] = i * j;
    }
}

This loop initializes the elements of the myArray array with the multiplication table values.

 

ArrayList in Java

An ArrayList is a dynamic array in Java, which means its size can be changed at runtime. It is implemented in the java.util package and is part of the Java Collections Framework. An ArrayList is similar to an array, but it provides additional functionality that makes it more flexible and easier to use.

An ArrayList can store elements of any data type, including objects, and it can grow or shrink dynamically as elements are added or removed. To create an ArrayList, you can use the following syntax:

ArrayList<datatype> arrayListName = new ArrayList<>();

Here, datatype is the type of elements that the ArrayList will store, and arrayListName is the name of the ArrayList. For example, to create an ArrayList of integers, you can use the following code:

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

Once an ArrayList is created, you can add elements to it using the add() method. For example, to add an integer to the myList ArrayList, you can use the following code:

myList.add(10);

You can also add elements to a specific index in the ArrayList using the add(index, element) method. For example, to add an integer to the second index of the myList ArrayList, you can use the following code:

myList.add(1, 20);

To access elements in an ArrayList, you can use the get(index) method, which returns the element at the specified index. For example, to get the first element in the myList ArrayList, you can use the following code:

int firstElement = myList.get(0);

You can also modify elements in an ArrayList using the set(index, element) method, which replaces the element at the specified index with a new element. For example, to replace the second element in the myList ArrayList with a new value, you can use the following code:

myList.set(1, 30);

To remove elements from an ArrayList, you can use the remove(index) method, which removes the element at the specified index, or the remove(object) method, which removes the first occurrence of the specified object from the ArrayList. For example, to remove the third element from the myList ArrayList, you can use the following code:

myList.remove(2);

Finally, to get the size of an ArrayList, you can use the size() method, which returns the number of elements in the ArrayList. For example, to get the size of the myList ArrayList, you can use the following code:

int size = myList.size();

In summary, an ArrayList in Java is a dynamic array that can store elements of any data type and can grow or shrink dynamically as elements are added or removed. It provides methods for adding, accessing, modifying, and removing elements, as well as getting the size of the ArrayList.

 

Difference - Array Vs ArrayList in Java

Now we have already discussed the basics of array and ArrayList in java, let us now jump into the difference between an array and ArrayList in Java.

Parameter Array ArrayList
Definition A fixed-size, homogeneous data structure that can store elements of a single data type. A dynamic-size, homogeneous data structure that can store elements of a single object type (does not support primitive types).
Memory Allocation Memory is allocated statically at the time of creation. Memory is allocated dynamically as the list grows and shrinks.
Data Type Support Supports both primitive data types (e.g., int, char) and objects. Supports only objects; use wrapper classes for primitive data types (e.g., Integer for int, Character for char).
Resizing Cannot be resized once created; a new array must be created to change its size. Resizes automatically as elements are added or removed.
Capacity Management No built-in capacity management; must be handled manually. Capacity management is built-in, with methods like ensureCapacity() and trimToSize().
Insertion and Deletion Manual shifting of elements required; may cause performance issues. Built-in methods for insertion and deletion (e.g., add(), remove()); more efficient.
Iteration Can use for loop, for-each loop, and while loop. Can use for loop, for-each loop, while loop, and iterator.
Synchronization Not synchronized; thread-safe in single-threaded environments. Not synchronized; use Collections.synchronizedList() or a concurrent alternative (e.g., CopyOnWriteArrayList) for multi-threaded environments.
Conversion No direct methods for conversion; must use loops or Arrays.asList(). Can use toArray() method to convert an ArrayList to an array.

 

Summary

In conclusion, the "array vs ArrayList" debate in Java revolves around the distinct characteristics and trade-offs associated with these data structures. Arrays are fixed-size, supporting both primitive types and objects, and require manual capacity management. ArrayLists, on the other hand, are dynamic-size and support only objects, but provide built-in capacity management and more efficient manipulation methods. Iterating over elements is similar for both, with ArrayLists additionally supporting iterators. Synchronization and thread-safety concerns need to be addressed for both data structures in multi-threaded environments.

Ultimately, the choice between array and ArrayList largely depends on the specific requirements of your project. By understanding the "array vs ArrayList" differences and their respective strengths and weaknesses, you can make informed decisions when selecting the most suitable data structure for your Java applications.

 

Further readings

Arrays in java
ArrayList in java

 

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Bashir Alam

He is a Computer Science graduate from the University of Central Asia, currently employed as a full-time Machine Learning Engineer at uExel. His expertise lies in OCR, text extraction, data preprocessing, and predictive models. You can reach out to him on his Linkedin or check his projects on GitHub page.

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