int[] numbers1 = new int[3]; // Array for 3 int values, default value is 0
int[] numbers2 = { 1, 2, 3 }; // Array literal of 3 int values
int[] numbers3 = new int[] { 1, 2, 3 }; // Array of 3 int values initialized
int[][] numbers4 = { { 1, 2 }, { 3, 4, 5 } }; // Jagged array literal
int[][] numbers5 = new int[5][]; // Jagged array, one dimension 5 long
int[][] numbers6 = new int[5][4]; // Multidimensional array: 5x4
Arrays may be created using any primitive or reference type.
float[] boats = new float[5]; // Array of five 32-bit floating point numbers.
double[] header = new double[] { 4.56, 332.267, 7.0, 0.3367, 10.0 };
// Array of five 64-bit floating point numbers.
String[] theory = new String[] { "a", "b", "c" };
// Array of three strings (reference type).
Object[] dArt = new Object[] { new Object(), "We love Stack Overflow.", new Integer(3) };
// Array of three Objects (reference type).
For the last example, note that subtypes of the declared array type are allowed in the array.
Arrays for user defined types can also be built similar to primitive types
UserDefinedClass[] udType = new UserDefinedClass[5];
// Parameters require objects, not primitives
// Auto-boxing happening for int 127 here
Integer[] initial = { 127, Integer.valueOf( 42 ) };
List<Integer> toList = Arrays.asList( initial ); // Fixed size!
// Note: Works with all collections
Integer[] fromCollection = toList.toArray( new Integer[toList.size()] );
//Java doesn't allow you to create an array of a parameterized type
List<String>[] list = new ArrayList<String>[2]; // Compilation error!
// Streams - JDK 8+
Stream<Integer> toStream = Arrays.stream( initial );
Integer[] fromStream = toStream.toArray( Integer[]::new );
An array is a data structure that holds a fixed number of primitive values or references to object instances.
Each item in an array is called an element, and each element is accessed by its numerical index. The length of an array is established when the array is created:
int size = 42;
int[] array = new int[size];
The size of an array is fixed at runtime when initialized. It cannot be changed after initialization. If the size must be mutable at runtime, a [Collection](<http://stackoverflow.com/documentation/java/90/collections>) class such as [ArrayList](<https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html>) should be used instead. ArrayList stores elements in an array and supports resizing by allocating a new array and copying elements from the old array.
If the array is of a primitive type, i.e.
int[] array1 = { 1,2,3 };
int[] array2 = new int[10];
the values are stored in the array itself. In the absence of an initializer (as in array2 above), the default value assigned to each element is 0 (zero).
If the array type is an object reference, as in