Java Language - 9 - Arrays and Multidimensional Arrays

Java Fundamentals – Arrays and Multidimensional Arrays

Introduction

Arrays are a fundamental data structure in Java that allow you to store multiple values of the same data type in a single variable. Multidimensional arrays take this concept further, allowing you to create arrays of arrays. In this guide, we’ll explore the use of arrays and multidimensional arrays in Java.

Single-Dimensional Arrays

Single-dimensional arrays, often referred to simply as arrays, are used to store collections of data of the same type. You can think of them as containers that hold multiple elements.


int[] numbers = {1, 2, 3, 4, 5};
String[] names = {"Alice", "Bob", "Charlie"};

In the examples above, we’ve created arrays to store integers and strings. You can access individual elements using index notation, such as ‘numbers[0]’ to access the first element.

Array Length and Iteration

The length of an array is the number of elements it can hold. You can access this information using the ‘length’ property. Iterating through an array is a common operation, and you can use ‘for’ loops to do so.


int[] numbers = {1, 2, 3, 4, 5};
int sum = 0;

for (int i = 0; i < numbers.length; i++) {
    sum += numbers[i];
}

In this example, we calculate the sum of all elements in the ‘numbers’ array using a ‘for’ loop.

Array Initialization and Dynamic Sizing

Arrays can be initialized with a fixed size, but Java also allows you to create arrays of dynamic size using ‘ArrayLists.’ An ‘ArrayList’ is a resizable array implementation that can grow or shrink as needed.


ArrayList<String> names = new ArrayList<>();
names.add("Alice");
names.add("Bob");
names.add("Charlie");

‘ArrayLists’ are flexible and useful when you don’t know the exact size of your collection in advance.

Multidimensional Arrays

Multidimensional arrays are arrays of arrays. They are often used to represent grids, matrices, or tables. You can have two-dimensional, three-dimensional, or even higher-dimensional arrays.


int[][] matrix = {
    {1, 2, 3},
    {4, 5, 6},
    {7, 8, 9}
};

In this example, we’ve created a two-dimensional array that represents a 3×3 matrix. You can access elements using row and column indices, like ‘matrix[1][2]’ to access the value 6.

Iteration Over Multidimensional Arrays

When iterating through multidimensional arrays, you typically use nested loops. The outer loop traverses the rows, while the inner loop goes through the columns.


int[][] matrix = {
    {1, 2, 3},
    {4, 5, 6},
    {7, 8, 9}
};

for (int i = 0; i < matrix.length; i++) {
    for (int j = 0; j < matrix[i].length; j++) {
        System.out.print(matrix[i][j] + " ");
    }
    System.out.println();
}

This nested ‘for’ loop structure allows you to access and process each element in a multidimensional array systematically.

Conclusion

Arrays and multidimensional arrays are essential data structures in Java that provide a way to manage and work with collections of data. Understanding their use, initialization, and iteration is key to developing versatile and robust Java applications.

Java Language – 9 – Arrays and Multidimensional Arrays