Understanding Java Arrays for DSA

In Java, arrays are a fundamental data structure that stores a fixed-size sequential collection of elements of the same type.

Declaration

dataType[] arrayName;

Example:

int[] numbers;

Initialization

Arrays can be initialized in several ways:

1. Using the new Keyword

    int[] numbers = new int[5]; // Creates an array of 5 zeros
   

2. Directly with values

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

3. Combining declaration and initialization

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

Accessing Elements

Elements of an array are accessed using their index. The index starts from 0.

int[] numbers = {1, 2, 3, 4, 5};
System.out.println(numbers[0]); // Outputs: 1

Array Length

The length of an array can be obtained using the length property.

int[] numbers = {1, 2, 3, 4, 5};
System.out.println(numbers.length); // Outputs: 5

Multidimensional Arrays

Java supports multidimensional arrays, which are arrays of arrays.

1. Declaration

    int[][] matrix = new int[3][3];
   

2. Initialization

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

Array Methods

Java provides several utility methods for arrays in the java.util.Arrays class.

1. Sorting

    int[] numbers = {5, 3, 4, 1, 2};
    Arrays.sort(numbers);
   

2. Searching

    int[] numbers = {1, 2, 3, 4, 5};
    int index = Arrays.binarySearch(numbers, 3);
   

3. Filling

    int[] numbers = new int[5];
    Arrays.fill(numbers, 10);
   

4. Copying

    int[] numbers = {1, 2, 3, 4, 5};
    int[] copy = Arrays.copyOf(numbers, numbers.length);
   

Array Limitations

1. Fixed Size: Once an array is created, its size cannot be changed.

2. Homogeneous: All elements in an array must be of the same type.

Array of Objects

Arrays can also hold objects.

String[] names = new String[3];
names[0] = "Alice";
names[1] = "Bob";
names[2] = "Charlie";

Enhanced for Loop

Java provides an enhanced for loop to iterate over arrays.

int[] numbers = {1, 2, 3, 4, 5};
for (int number : numbers) {
    System.out.println(number);
}

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