Arrays Class

1import java.util.Arrays;
2
3// toString() - Print array contents
4int[] arr = {5, 2, 8, 1, 9};
5System.out.println(arr);                    // [I@hashcode (useless!)
6System.out.println(Arrays.toString(arr));   // [5, 2, 8, 1, 9]
7
8// For 2D arrays, use deepToString()
9int[][] matrix = {{1, 2}, {3, 4}};
10System.out.println(Arrays.deepToString(matrix));  // [[1, 2], [3, 4]]
11
12// sort() - Sort array
13int[] nums = {5, 2, 8, 1, 9};
14Arrays.sort(nums);
15System.out.println(Arrays.toString(nums));  // [1, 2, 5, 8, 9]
16
17// Sort range only
18int[] partial = {5, 2, 8, 1, 9};
19Arrays.sort(partial, 1, 4);  // Sort indices 1 to 3
20System.out.println(Arrays.toString(partial));  // [5, 1, 2, 8, 9]

1// binarySearch() - Search in SORTED array
2int[] sorted = {1, 2, 5, 8, 9};
3int index = Arrays.binarySearch(sorted, 5);
4System.out.println("Index of 5: " + index);  // 2
5
6// Not found returns -(insertion point) - 1
7int notFound = Arrays.binarySearch(sorted, 6);
8System.out.println("Index of 6: " + notFound);  // -4
9
10// equals() - Compare arrays
11int[] a = {1, 2, 3};
12int[] b = {1, 2, 3};
13int[] c = {1, 2, 4};
14
15System.out.println(a == b);                    // false (different objects)
16System.out.println(Arrays.equals(a, b));       // true (same content)
17System.out.println(Arrays.equals(a, c));       // false
18
19// For 2D arrays, use deepEquals()
20int[][] m1 = {{1, 2}, {3, 4}};
21int[][] m2 = {{1, 2}, {3, 4}};
22System.out.println(Arrays.deepEquals(m1, m2));  // true

1// fill() - Fill array with value
2int[] zeros = new int[5];
3Arrays.fill(zeros, 0);
4System.out.println(Arrays.toString(zeros));  // [0, 0, 0, 0, 0]
5
6// Fill range
7int[] arr = new int[5];
8Arrays.fill(arr, 1, 4, 9);  // Fill indices 1-3 with 9
9System.out.println(Arrays.toString(arr));  // [0, 9, 9, 9, 0]
10
11// copyOf() - Copy array
12int[] original = {1, 2, 3, 4, 5};
13int[] copy = Arrays.copyOf(original, original.length);
14int[] larger = Arrays.copyOf(original, 10);  // Extends with zeros
15int[] smaller = Arrays.copyOf(original, 3);  // Truncates
16
17System.out.println(Arrays.toString(larger));   // [1, 2, 3, 4, 5, 0, 0, 0, 0, 0]
18System.out.println(Arrays.toString(smaller));  // [1, 2, 3]
19
20// copyOfRange() - Copy range
21int[] range = Arrays.copyOfRange(original, 1, 4);
22System.out.println(Arrays.toString(range));  // [2, 3, 4]

1// asList() - Convert array to List
2String[] names = {"Alice", "Bob", "Charlie"};
3List<String> list = Arrays.asList(names);
4System.out.println(list);  // [Alice, Bob, Charlie]
5
6// Warning: List is backed by array!
7list.set(0, "Anna");
8System.out.println(names[0]);  // Anna (array also changed!)
9
10// Cannot add/remove elements
11// list.add("Dave");  // UnsupportedOperationException!
12
13// For modifiable list:
14List<String> modifiable = new ArrayList<>(Arrays.asList(names));
15
16// stream() - Create stream from array (Java 8+)
17int[] numbers = {1, 2, 3, 4, 5};
18int sum = Arrays.stream(numbers).sum();
19int max = Arrays.stream(numbers).max().orElse(0);
20
21System.out.println("Sum: " + sum);  // 15
22System.out.println("Max: " + max);  // 5
23
24// parallelSort() - Faster for large arrays
25int[] large = new int[1000000];
26Arrays.parallelSort(large);  // Uses multiple threads