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Array in Java is a group of like-typed variables referred to by a common name. Arrays in Java work differently than they do in C/C++. Following are some important points about Java arrays.
In Java, all arrays are dynamically allocated. (discussed below)
Arrays are stored in contiguous memory [consecutive memory locations].
Since arrays are objects in Java, we can find their length using the object property length. This is different from C/C++, where we find length using sizeof.
A Java array variable can also be declared like other variables with [] after the data type.
The variables in the array are ordered, and each has an index beginning with 0.
Java array can also be used as a static field, a local variable, or a method parameter.
The size of an array must be specified by int or short value and not long.
The direct superclass of an array type is Object.
Every array type implements the interfaces Cloneable and java.io.Serializable.
This storage of arrays helps us randomly access the elements of an array [Support Random Access].
The size of the array cannot be altered(once initialized). However, an array reference can be made to point to another array.
An array can contain primitives (int, char, etc.) and object (or non-primitive) references of a class depending on the definition of the array. In the case of primitive data types, the actual values are stored in contiguous memory locations. In the case of class objects, the actual objects are stored in a heap segment.
Creating, initializing, and accessing an Array
general form of a one-dimensional array declaration is
type var-name[];
OR
type[] var-name;
An array declaration has two components: the type and the name.
Type declares the element type of the array. The element type determines the data type of each element that comprises the array. Like an array of integers, we can also create an array of other primitive data types like char, float, double, etc., or user-defined data types (objects of a class). Thus, the element type for the array determines what type of data the array will hold.
// both are valid declarations
int intArray[];
or int[] intArray;
byte byteArray[];
short shortsArray[];
boolean booleanArray[];
long longArray[];
float floatArray[];
double doubleArray[];
char charArray[];
// an array of references to objects of
// the class MyClass (a class created by
// user)
MyClass myClassArray[];
Object[] ao, // array of Object
Collection[] ca; // array of Collection
// of unknown type
Although the first declaration establishes that int Array is an array variable, no actual array exists. It merely tells the compiler that this variable (int Array) will hold an array of the integer type. To link int Array with an actual, physical array of integers, you must allocate one using new and assign it to int Array.
When an array is declared, only a reference of an array is created. To create or give memory to the array, you create an array like this: The general form of new as it applies to one-dimensional arrays appears as follows:
var-name = new type [size];
Here, type specifies the type of data being allocated, size determines the number of elements in the array, and var-name is the name of the array variable that is linked to the array. To use new to allocate an array, you must specify the type and number of elements to allocate.
int intArray[]; //declaring array
intArray = new int[20]; // allocating memory to array
In a situation where the size of the array and variables of the array are already known, array literals can be used.
int[] intArray = new int[]{ 1,2,3,4,5,6,7,8,9,10 };
// Declaring array literal
The length of this array determines the length of the created array. There is no need to write the new int[] part in the latest versions of Java.
Each element in the array is accessed via its index. The index begins with 0 and ends at (total array size)-1. All the elements of array can be accessed using Java for Loop.
// accessing the elements of the specified array
for (int i = 0; i < arr.length; i++)
System.out.println("Element at index " + i +
" : "+ arr[i]);
// Java program to illustrate creating an array
// of integers, puts some values in the array,
// and prints each value to standard output.
class GFG {
public static void main(String[] args)
{
// declares an Array of integers.
int[] arr;
// allocating memory for 5 integers.
arr = new int[5];
// initialize the first elements of the array
arr[0] = 10;
// initialize the second elements of the array
arr[1] = 20;
// so on...
arr[2] = 30;
arr[3] = 40;
arr[4] = 50;
// accessing the elements of the specified array
for (int i = 0; i < arr.length; i++)
System.out.println("Element at index " + i
+ " : " + arr[i]);
}
}Output:
Element at index 0 : 10
Element at index 1 : 20
Element at index 2 : 30
Element at index 3 : 40
Element at index 4 : 50
An array of objects is created like an array of primitive-type data items in the following way.
1) data type[] arrName;
2) datatype arrName[];
3) datatype [] arrName;
// Java program to illustrate creating
// an array of objects
class Student {
public int roll_no;
public String name;
Student(int roll_no, String name)
{
this.roll_no = roll_no;
this.name = name;
}
}
// Elements of the array are objects of a class Student.
public class GFG {
public static void main(String[] args)
{
// declares an Array of integers.
Student[] arr;
// allocating memory for 5 objects of type Student.
arr = new Student[5];
// initialize the first elements of the array
arr[0] = new Student(1, "aman");
// initialize the second elements of the array
arr[1] = new Student(2, "vaibhav");
// so on...
arr[2] = new Student(3, "shikar");
arr[3] = new Student(4, "dharmesh");
arr[4] = new Student(5, "mohit");
// accessing the elements of the specified array
for (int i = 0; i < arr.length; i++)
System.out.println("Element at " + i + " : "
+ arr[i].roll_no + " "
+ arr[i].name);
}
}
Output:
Element at 0 : 1 aman
Element at 1 : 2 vaibhav
Element at 2 : 3 shikar
Element at 3 : 4 dharmesh
Element at 4 : 5 mohit
JVM throws ArrayIndexOutOfBoundsException to indicate that the array has been accessed with an illegal index. The index is either negative or greater than or equal to the size of an array.
Below code shows what happens if we try to access elements outside the array size.
// Code for showing error "ArrayIndexOutOfBoundsException"
public class GFG {
public static void main(String[] args)
{
int[] arr = new int[4];
arr[0] = 10;
arr[1] = 20;
arr[2] = 30;
arr[3] = 40;
System.out.println(
"Trying to access element outside the size of array");
System.out.println(arr[5]);
}
}Ouput
Trying to access element outside the size of array
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: Index 5 out of bounds for length 4
at GFG.main(GFG.java:13)
Multidimensional arrays are arrays of arrays with each element of the array holding the reference of other arrays. These are also known as Jagged Arrays. A multidimensional array is created by appending one set of square brackets ([]) per dimension.
datatype [][] arrayrefvariable;
or
datatype arrayrefvariable[][];
Example
public class multiDimensional {
public static void main(String args[])
{
// declaring and initializing 2D array
int arr[][]
= { { 2, 7, 9 }, { 3, 6, 1 }, { 7, 4, 2 } };
// printing 2D array
for (int i = 0; i < 3; i++) {
for (int j = 0; j < 3; j++)
System.out.print(arr[i][j] + " ");
System.out.println();
}
}
}Output
2 7 9
3 6 1
7 4 2
Like variables, we can also pass arrays to methods. For example, the below program passes the array to method sum to calculate the sum of the array’s values.
Example
// Java program to demonstrate
// passing of array to method
public class Test {
// Driver method
public static void main(String args[])
{
int arr[] = { 3, 1, 2, 5, 4 };
// passing array to method m1
sum(arr);
}
public static void sum(int[] arr)
{
// getting sum of array values
int sum = 0;
for (int i = 0; i < arr.length; i++)
sum += arr[i];
System.out.println("sum of array values : " + sum);
}
}Output
sum of array values : 15
As usual, a method can also return an array. For example, the below program returns an array from method m1.
Example
// Java program to demonstrate
// return of array from method
class Test {
// Driver method
public static void main(String args[])
{
int arr[] = m1();
for (int i = 0; i < arr.length; i++)
System.out.print(arr[i] + " ");
}
public static int[] m1()
{
// returning array
return new int[] { 1, 2, 3 };
}
}Output
1 2 3
Every array has an associated Class object, shared with all other arrays with the same component type.
Example
// Java program to demonstrate
// Class Objects for Arrays
class Test {
public static void main(String args[])
{
int intArray[] = new int[3];
byte byteArray[] = new byte[3];
short shortsArray[] = new short[3];
// array of Strings
String[] strArray = new String[3];
System.out.println(intArray.getClass());
System.out.println(
intArray.getClass().getSuperclass());
System.out.println(byteArray.getClass());
System.out.println(shortsArray.getClass());
System.out.println(strArray.getClass());
}
}Output
class [I
class java.lang.Object
class [B
class [S
class [Ljava.lang.String;
Now, as you know that arrays are objects of a class, and a direct superclass of arrays is a class Object. The members of an array type are all of the following:
1)The public final field length contains the number of components of the array. Length may be positive or zero.
2)All the members are inherited from class Object; the only method of Object that is not inherited is its clone method.
3)The public method clone() overrides the clone method in class Object and throws no checked exceptions.
When you clone a single-dimensional array, such as Object[], a “deep copy” is performed with the new array containing copies of the original array’s elements as opposed to references.
// Java program to demonstrate
// cloning of one-dimensional arrays
class Test {
public static void main(String args[])
{
int intArray[] = { 1, 2, 3 };
int cloneArray[] = intArray.clone();
// will print false as deep copy is created
// for one-dimensional array
System.out.println(intArray == cloneArray);
for (int i = 0; i < cloneArray.length; i++) {
System.out.print(cloneArray[i] + " ");
}
}
}Output
false
1 2 3
A clone of a multi-dimensional array (like Object[][]) is a “shallow copy,” however, which is to say that it creates only a single new array with each element array a reference to an original element array, but subarrays are shared.
// Java program to demonstrate
// cloning of multi-dimensional arrays
class Test {
public static void main(String args[])
{
int intArray[][] = { { 1, 2, 3 }, { 4, 5 } };
int cloneArray[][] = intArray.clone();
// will print false
System.out.println(intArray == cloneArray);
// will print true as shallow copy is created
// i.e. sub-arrays are shared
System.out.println(intArray[0] == cloneArray[0]);
System.out.println(intArray[1] == cloneArray[1]);
}
}Output
false
true
true
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