Java Arrays

public class Arrays1D {
    public static void main(String[] args) {
        // Declaration and allocation
        int[] scores = new int[5];   // default values: 0

        // Initialization
        scores[0] = 90;
        scores[1] = 85;
        scores[2] = 78;
        scores[3] = 92;
        scores[4] = 88;

        // Array literal (declare + initialize at once)
        String[] fruits = {"Apple", "Banana", "Cherry", "Date"};

        // Access elements
        System.out.println("First score: " + scores[0]);   // 90
        System.out.println("Last fruit:  " + fruits[fruits.length - 1]);  // Date

        // Iterate with for-each
        int sum = 0;
        for (int s : scores) {
            sum += s;
        }
        System.out.println("Average: " + (sum / scores.length));  // 86
    }
}

public class Arrays2D {
    public static void main(String[] args) {
        // 2D array (3 rows, 3 columns)
        int[][] matrix = {
            {1, 2, 3},
            {4, 5, 6},
            {7, 8, 9}
        };

        // Access element at row 1, column 2
        System.out.println(matrix[1][2]);  // 6

        // Print entire matrix
        for (int[] row : matrix) {
            for (int val : row) {
                System.out.printf("%3d", val);
            }
            System.out.println();
        }

        // Jagged array — rows have different lengths
        int[][] jagged = new int[3][];
        jagged[0] = new int[]{1};
        jagged[1] = new int[]{2, 3};
        jagged[2] = new int[]{4, 5, 6};

        for (int[] row : jagged) {
            for (int v : row) System.out.print(v + " ");
            System.out.println();
        }
    }
}

import java.util.Arrays;

public class ArraysUtil {
    public static void main(String[] args) {
        int[] nums = {5, 2, 8, 1, 9, 3};

        // sort — ascending order
        Arrays.sort(nums);
        System.out.println(Arrays.toString(nums));  // [1, 2, 3, 5, 8, 9]

        // binarySearch — array must be sorted first
        int idx = Arrays.binarySearch(nums, 8);
        System.out.println("Index of 8: " + idx);  // 4

        // fill — set all elements to a value
        int[] filled = new int[5];
        Arrays.fill(filled, 7);
        System.out.println(Arrays.toString(filled));  // [7, 7, 7, 7, 7]

        // copyOf — copy with new length
        int[] copy = Arrays.copyOf(nums, 4);
        System.out.println(Arrays.toString(copy));  // [1, 2, 3, 5]

        // copyOfRange — copy a slice
        int[] slice = Arrays.copyOfRange(nums, 2, 5);
        System.out.println(Arrays.toString(slice));  // [3, 5, 8]

        // equals — compare two arrays
        int[] a = {1, 2, 3};
        int[] b = {1, 2, 3};
        System.out.println(Arrays.equals(a, b));  // true
    }
}