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How do you declare, initialize, and access elements of a one-dimensional array in Java? How do you declare and initialize an array of objects (reference types) versus an array of primitives, and what is the key difference in their default values? How do multidimensional arrays work in Java, and how do they differ from truly rectangular arrays in languages like C? How do you convert between an array and a List (ArrayList) in both directions, and what pitfalls exist with Arrays.asList()? How does Java handle array bounds checking, and what exception is thrown when accessing an invalid index? How do you correctly iterate a 2D array using both traditional indexed for-loops and the enhanced for-each loop, and when is each approach preferable? What is array covariance's relationship to generic arrays, and why can't you directly create a generic array like new T[10] or new List<String>[10]? How would you flatten a 2D array into a 1D array, and conversely, reshape a 1D array into a 2D array? How does Java implement covariant array typing, and why is this considered a design flaw that can lead to runtime ArrayStoreException? How would you efficiently copy, resize, or merge large arrays in Java, and what are the performance trade-offs between System.arraycopy(), Arrays.copyOf(), and manual loops?
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What utility methods does java.util.Arrays provide for common array operations like sorting, searching, filling, and comparing?

Intermediate

Answer

Arrays provides static utility methods including sort() (in-place sorting, dual-pivot quicksort for primitives, TimSort for objects), binarySearch() (requires a pre-sorted array), fill() (populate all elements with one value), copyOf()/copyOfRange() (create a resized copy), equals()/deepEquals() (element-wise comparison, deepEquals needed for nested arrays), and asList() (a fixed-size List view backed by the array) -- these cover the vast majority of common array manipulation needs without hand-writing loops.
int[] nums = {5, 2, 8, 1, 9};
Arrays.sort(nums);  // {1, 2, 5, 8, 9}
int index = Arrays.binarySearch(nums, 8);  // 3

int[] copy = Arrays.copyOf(nums, 3);  // {1, 2, 5}
int[][] matrix1 = {{1,2},{3,4}};
int[][] matrix2 = {{1,2},{3,4}};
System.out.println(Arrays.equals(matrix1, matrix2));      // false -- compares references of inner arrays
System.out.println(Arrays.deepEquals(matrix1, matrix2));  // true -- recursively compares contents
Real-world example A data-processing utility sorts a large primitive int array using Arrays.sort() (leveraging its highly optimized dual-pivot quicksort implementation) rather than converting to a boxed Integer collection just to use Collections.sort(), avoiding unnecessary boxing overhead for a purely numeric workload.

Common follow-ups: Why does Arrays.equals() give a misleading false result for nested arrays, requiring deepEquals() instead?;What are the performance characteristics of Arrays.sort() for primitives versus objects?

Collections Framework;Generics
All 15 Arrays & Multidimensional Arrays questions