Arrays in Java

Arrays in Java

In Java, the Arrays class is a utility class from the java.util package that provides a collection of static methods for working with arrays. It helps you perform common tasks like sorting, searching, comparing, filling, and converting arrays to strings without writing all the low-level loops yourself.

Importing

import java.util.Arrays;

Common Methods in Arrays

Here’s a breakdown of the most important ones:

1. Sorting

int[] numbers = {5, 3, 8, 1};
Arrays.sort(numbers);  // Sorts in ascending order
System.out.println(Arrays.toString(numbers)); // [1, 3, 5, 8]
  • Can sort primitive arrays (int[], double[], etc.) and object arrays (String[]).
  • For custom sorting, use Arrays.sort(array, comparator).

2. Searching

int[] numbers = {1, 3, 5, 8};
int index = Arrays.binarySearch(numbers, 5); // Works on sorted arrays
System.out.println(index); // 2
  • Returns index if found, otherwise -(insertion_point) - 1.

3. Converting to String

String[] names = {"Alice", "Bob", "Charlie"};
System.out.println(Arrays.toString(names)); // [Alice, Bob, Charlie]
  • For multidimensional arrays, use:
int[][] matrix = {{1, 2}, {3, 4}};
System.out.println(Arrays.deepToString(matrix)); // [[1, 2], [3, 4]]

4. Filling

int[] arr = new int[5];
Arrays.fill(arr, 7);  // Fill entire array with 7
System.out.println(Arrays.toString(arr)); // [7, 7, 7, 7, 7]
  • Overloaded version lets you fill part of an array.

5. Comparing

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

int[][] x = {{1, 2}, {3, 4}};
int[][] y = {{1, 2}, {3, 4}};
System.out.println(Arrays.deepEquals(x, y)); // true

6. Copying

int[] original = {1, 2, 3};
int[] copy = Arrays.copyOf(original, 5); // Extra space filled with zeros
System.out.println(Arrays.toString(copy)); // [1, 2, 3, 0, 0]
  • Arrays.copyOfRange(array, from, to) copies a portion.

7. Parallel Sorting (Java 8+)

int[] numbers = {5, 3, 8, 1};
Arrays.parallelSort(numbers);
System.out.println(Arrays.toString(numbers)); // [1, 3, 5, 8]
  • Uses multiple threads for large arrays.

Key Notes

  • Arrays only works for arrays, not collections like ArrayList (for those, use Collections class).
  • It’s a final class, so you cannot extend it.
  • All methods are static, so you use them with the class name (e.g., Arrays.sort(...)).

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