MATH, ARRAYS, WRAPPERS
Array Operations and Utilities
Rule: Arrays class provides utility methods for common array operations like sorting, searching, and comparison.
import java.util.Arrays;
// Array creation and initialization
int[] numbers = {5, 2, 8, 1, 9};
String[] names = new String[3];
Arrays.fill(names, "Unknown"); // Fill entire array with value
// Sorting
Arrays.sort(numbers); // [1, 2, 5, 8, 9]
String[] words = {"zebra", "apple", "banana"};
Arrays.sort(words); // [apple, banana, zebra]
// Partial sorting
int[] partialSort = {5, 2, 8, 1, 9, 3, 7};
Arrays.sort(partialSort, 1, 4); // Sort indices 1-3: [5, 1, 2, 8, 9, 3, 7]
// Array copying
int[] original = {1, 2, 3, 4, 5};
int[] copy1 = Arrays.copyOf(original, 3); // [1, 2, 3]
int[] copy2 = Arrays.copyOf(original, 7); // [1, 2, 3, 4, 5, 0, 0]
int[] copy3 = Arrays.copyOfRange(original, 1, 4); // [2, 3, 4]
// Array equality
int[] arr1 = {1, 2, 3};
int[] arr2 = {1, 2, 3};
int[] arr3 = {1, 2, 4};
System.out.println(arr1 == arr2); // false (reference comparison)
System.out.println(Arrays.equals(arr1, arr2)); // true (content comparison)
System.out.println(Arrays.equals(arr1, arr3)); // false (different content)
// Multi-dimensional arrays
int[][] matrix1 = {{1, 2}, {3, 4}};
int[][] matrix2 = {{1, 2}, {3, 4}};
System.out.println(Arrays.equals(matrix1, matrix2)); // false (shallow comparison)
System.out.println(Arrays.deepEquals(matrix1, matrix2)); // true (deep comparison)
Array to String conversion:
int[] array = {1, 2, 3, 4, 5};
System.out.println(array); // [I@hashcode (not useful)
System.out.println(Arrays.toString(array)); // [1, 2, 3, 4, 5]
int[][] twoDArray = {{1, 2}, {3, 4}};
System.out.println(Arrays.toString(twoDArray)); // [references] (not useful)
System.out.println(Arrays.deepToString(twoDArray)); // [[1, 2], [3, 4]]
💡 Learning Tip: Remember “ARRAYS = UTILITY BELT” - Arrays class has tools for every common array operation. Use deepEquals() and deepToString() for multi-dimensional arrays.
Q: What’s the difference between Arrays.equals() and Arrays.deepEquals()?
A: equals() does shallow comparison (one level), while deepEquals() recursively compares multi-dimensional arrays.