Java Data Structures: Arrays

Java provides a fundamental data structure for storing sequences of elements of the same type: the array. While seemingly simple, understanding its characteristics is crucial for efficient programming.

Array Declaration and Initialization

Arrays are declared using square brackets [], specifying the element type and optionally the size. Initialization can be done explicitly by listing elements within curly braces {} or implicitly, leaving elements uninitialized (with default values).

Example: int[] numbers = new int[5]; or String[] names = {"Alice", "Bob", "Charlie"};

One-Dimensional Arrays

The most basic form, a one-dimensional array represents a linear sequence of elements. Elements are accessed using zero-based indexing.

Example: Accessing the second element of numbers: numbers[1]

Multi-Dimensional Arrays

Java supports arrays of arrays, creating multi-dimensional structures. These are typically used to represent matrices or tables. The number of dimensions is not fixed at compile time; arrays of arrays can be created dynamically.

Example: A two-dimensional array: int[][] matrix = new int[3][4];

Array Length and Manipulation

The length property provides the number of elements in an array. Arrays are fixed in size after creation; resizing requires creating a new array and copying elements.

Java's Arrays class provides utility methods for array manipulation, such as copying, sorting, and searching.

Primitive vs. Object Arrays

Arrays can hold either primitive data types (int, double, boolean, etc.) or object references. Object arrays allow storing instances of classes.

Considerations for Array Usage

Arrays are efficient for storing and accessing elements sequentially. However, inserting or deleting elements in the middle of an array requires shifting other elements, making these operations less efficient compared to data structures like ArrayList.