core8ArraysDemo

1package pkg1core;2 3/*4 * core8ArraysDemo.java5 * ---------------6 * 1D and 2D arrays, initialization, iteration, and java.util.Arrays utilities.7 *8 * EXPLANATION:9 *  - Arrays are fixed-size, zero-indexed, and store one type.10 *  - `arr.length` is a field (not a method).11 *  - java.util.Arrays provides sort, binarySearch, fill, copyOf, toString, etc.12 */13import java.util.Arrays;14 15public class core8ArraysDemo {16    public static void main(String[] args) {17        // Declaration + initialization18        int[] a = {5, 3, 8, 1, 9, 2};19        int[] b = new int[3];          // defaults to all zeros20        b[0] = 10; b[1] = 20; b[2] = 30;21 22        System.out.println("a = " + Arrays.toString(a));23        System.out.println("b = " + Arrays.toString(b) + " (length " + b.length + ")");24 25        // Sorting + binary search (array must be sorted for search)26        int[] sorted = a.clone();27        Arrays.sort(sorted);28        System.out.println("sorted = " + Arrays.toString(sorted));29        System.out.println("index of 8 = " + Arrays.binarySearch(sorted, 8));30 31        // Fill and copy32        int[] filled = new int[4];33        Arrays.fill(filled, 7);34        System.out.println("filled = " + Arrays.toString(filled));35        System.out.println("copyOf(a,3) = " + Arrays.toString(Arrays.copyOf(a, 3)));36 37        // 2D array (array of arrays)38        int[][] grid = {39            {1, 2, 3},40            {4, 5, 6}41        };42        System.out.println("2D grid:");43        for (int[] row : grid) {44            System.out.println("  " + Arrays.toString(row));45        }46        System.out.println("grid[1][2] = " + grid[1][2]);47 48        // Manual reverse in place49        for (int i = 0, j = a.length - 1; i < j; i++, j--) {50            int t = a[i]; a[i] = a[j]; a[j] = t;51        }52        System.out.println("reversed a = " + Arrays.toString(a));53    }54}