Array vs ArrayList in Java: Differences and When to Use Each
Array vs ArrayList in Java compared on size, capacity growth, boxing, type safety and Big-O cost, with a decision table and one-line conversions.
In Java, an array is a data structure used to store a collection of elements of the same data type. Arrays are fixed in size, which means that once you declare an array with a certain size, you cannot change that size during runtime.
Related Tags
Tutorials
Convert Primitive Array to List in Java (int[] to List)
Convert primitive array to List in Java with boxed().toList(), loops, Guava Ints.asList() and ArrayUtils, and learn why Arrays.asList(int[]) fails.
Convert String Array to int Array in Java (Safe Parsing)
Convert String array to int array in Java with streams and Integer.parseInt(), get an Integer[] and skip or report invalid values safely.
Java Arrays: Memory, Rules, Arrays Class and All Tutorials
Java arrays explained with memory layout, default values, rules and the Arrays class, plus every array tutorial grouped by task, from copy to conversion.
ArrayStoreException in Java: Causes and How to Fix It
Learn why ArrayStoreException happens with covariant arrays, System.arraycopy() and toArray(), how to read its message, and how to fix and prevent it.
Sum and Average of an Array in Java (Loop, Stream, Overflow)
Calculate the sum and average of an array in Java with a loop or IntStream, and avoid integer division, int overflow and empty-array traps.
Convert List to Array in Java and an Array Back to a List
Convert list to array in Java with the three toArray() methods, get an int[] from a list of Integer, and turn arrays back into lists with asList().
Java Stream to Array and Array to Stream Conversion
Convert a Java stream to array form with toArray() and a generator, and arrays to streams with Arrays.stream(), including int[], ranges and 2D arrays.
Remove an Element from an Array in Java: Index, Value, Filter
Learn to remove an element from an array in Java by index, value or condition with System.arraycopy(), streams, ArrayList and ArrayUtils.
Convert int[] to Integer[] in Java and Back to int[]
Convert int[] to Integer[] in Java with boxed() and back with mapToInt(), handle null elements, long, double and char arrays, and use ArrayUtils.
Split an Array in Java: At an Index, in Halves or in Chunks
Learn to split an array in Java at an index, into halves, into fixed-size chunks or N parts with Arrays.copyOfRange(), loops and Java 24 gatherers.
Concatenate Two Arrays in Java: arraycopy, Streams, Libraries
Learn to concatenate two arrays in Java with System.arraycopy(), Arrays.copyOf(), streams, ArrayUtils and Guava, for primitive and object arrays.
Check If Two Arrays Are Equal in Java (equals, deepEquals)
Check if two arrays are equal in Java with Arrays.equals(), deepEquals(), mismatch() and compare(), and fix array equality in records, sets and tests.
Check if an Array Is Sorted in Java (Ascending, Descending)
Check if an array is sorted in Java by comparing neighbors, with noneMatch(), a Comparator, case-insensitive strings, ArrayUtils and Guava.
Find Top N Elements in an Array in Java (Sort, Stream, Heap)
Find the top N elements in an array in Java by sorting a copy, with sorted().limit(), a PriorityQueue min-heap or Guava, for numbers and objects.
Find Max and Min in an Array in Java (Loop, Stream, Objects)
Find the max and min in an array in Java with one loop, IntStream max() and min(), summaryStatistics() or a Comparator, plus empty arrays and NaN.
Resize an Array in Java with Arrays.copyOf() and ArrayList
Java arrays have a fixed length, so we resize an array by copying it into a new one with Arrays.copyOf(). Learn the default values, the alias trap, inserting with System.arraycopy(), resizing 2D arrays and when an ArrayList fits better.
Reverse an Array in Java: In Place, Copy and List.reversed()
Learn to reverse an array in Java in place with a swap loop, into a new array, with Collections.reverse() and List.reversed(), and avoid the int[] trap.
Declare and Initialize an Array in Java (With Examples)
Learn to declare and initialize an array in Java with new, array initializers, Arrays.fill(), setAll(), streams and 2D arrays, plus all default values.
Union of Two Arrays in Java: Set, Stream and Sorted Merge
Find the union of two arrays in Java with LinkedHashSet, IntStream distinct() and a two-pointer merge for sorted input, with order and duplicates covered.
Intersection of Two Arrays in Java, With and Without Duplicates
Find the intersection of two arrays in Java with retainAll(), a HashSet filter, a count map for repeats and two pointers for sorted arrays.
Remove Duplicates from an Array in Java: Find, Count, Remove
Learn to find, count and remove duplicates from an array in Java with HashSet, frequency maps, distinct() and an in-place loop for sorted arrays.
Check if an Array Contains a Value in Java (int and String)
Learn to check if an array contains a value in Java with Arrays.asList(), anyMatch(), binarySearch() and HashSet, and why asList() fails on int[].
Copy an Array in Java: Shallow Copy vs Deep Copy
Learn to copy an array in Java with clone(), Arrays.copyOf() and System.arraycopy(), and how to make deep copies of object arrays and 2D arrays.
Convert String to String Array in Java with split()
Convert String to String array in Java with split(), handle regex delimiters, empty strings and emoji, and build a single-element array.
Create a Subarray in Java: copyOfRange(), arraycopy, Streams
Learn to create a subarray in Java with Arrays.copyOfRange(), copyOf(), System.arraycopy(), range streams and ArrayUtils, plus index rules and pitfalls.
Convert Byte Array to String in Java and String to byte[]
Convert byte array to String in Java with the right charset, go back with getBytes(), and use Base64 or HexFormat for binary data.
Join String Array in Java with Comma or Any Separator
Join String array in Java with String.join(), Collectors.joining() and StringJoiner, handle null and empty values, and join int arrays.
Print an Array in Java: toString(), deepToString() and Loops
Learn how to print an array in Java with Arrays.toString() and deepToString(), why println shows [I@ codes, custom formats, records and char[] output.