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Arrays in Java are a data structure that stores ordered collections of fixed-sized elements of the desired type.
- In Java, an array is used to store a collection of data, but it is often useful to think of an array as a collection of variables of the same type.
- Instead of declaring individual variables, such as number0, number1, ..., and number99, you declare one array variable, for example, numbers and use numbers [0], numbers [1], ..., and numbers [99] for mapping of individual variables.
- This article will introduce you to how to declare an array of variables in Java, create and manipulate an array using indexed variables.
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Declaring an array
To use an array in a program, you need to declare a variable to reference the array, and you must specify the type of the array that can reference the variable. The syntax for declaring an array variable is:
dataType[] arrayRefVar; // preferred way.
or
dataType arrayRefVar[]; // works but not preferred way.click below button to copy the code. By - java tutorial - team
Note: The style dataType[] arrayRefVar is preferred.
Sample Code
The following code snippets are examples of using this syntax:
double [] myList; // Preferred way.
or
double myList []; // Works, but is not the preferred way.click below button to copy the code. By - java tutorial - team
Creating an array
In Java, you can create an array using the new operator using the following syntax:
arrayRefVar = new dataType[arraySize];click below button to copy the code. By - java tutorial - team
The above declaration does two things:
- Creates an array using the new dataType [arraySize];
- A reference to the new created array is assigned to the variable arrayRefVar.
Declaring a variable, creating and assigning an array reference variable can be shown below:
dataType[] arrayRefVar = new dataType[arraySize];click below button to copy the code. By - java tutorial - team
Alternatively, arrays in Java can be created as follows:
dataType [] arrayRefVar = {value0, value1, ..., valuek};click below button to copy the code. By - java tutorial - team
- Array elements are available to the index. Indices are counted from 0; that is, they start from 0 to arrayRefVar.length-1.
Sample Code
- The following statement declares an array of variables myList, creates an array of 10 elements of type double and assigns the link myList:
double[] myList = new double[10];click below button to copy the code. By - java tutorial - team
- The image displays the array myList. Here myList has ten double values and indices from 0 to 9.
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Working with arrays
When working with array elements, the for loop or foreach loop is often used because all elements have the same type and known size.
Sample Code
A complete example showing how to create, initialize, and process an array:
public class TestArray {
public static void main (String [] args) {
double [] myList = {1.9, 2.9, 3.4, 3.5};
// Display all elements of the array
for (int i = 0; i <myList.length; i ++) {
System.out.println (myList [i] + "");
}
// Sum of array elements
double total = 0;
for (int i = 0; i <myList.length; i ++) {
total += myList [i];
}
System.out.println ("Sum of array numbers:" + total);
// Find the largest element in the array
double max = myList [0];
for (int i = 1; i <myList.length; i ++) {
if (myList [i]> max) max = myList [i];
}
System.out.println ("The largest element:" + max);
}
}click below button to copy the code. By - java tutorial - team
Output
1.9
2.9
3.4
3.5
Sum of array numbers:11.7
The largest element:3.5Foreach cycle
JDK 1.5 introduced a new for loop , known as a foreach loop or an extended for loop , which allows you to sequentially traverse an entire array without using a variable index.
Sample Code
The following code displays all the elements in the myList array:
public class TestArray {
public static void main(String[] args) {
double[] myList = {1.9, 2.9, 3.4, 3.5};
// Print all the array elements
for (double element: myList) {
System.out.println(element);
}
}
}click below button to copy the code. By - java tutorial - team
Output
1.9
2.9
3.4
3.5Passing an array to a method
- Just as you can pass primitive type values to methods, you can also pass arrays to methods. For example, the following method displays the elements in an int array −
public static void printArray(int[] array) {
for (int i = 0; i < array.length; i++) {
System.out.print(array[i] + " ");
}
}click below button to copy the code. By - java tutorial - team
- You can invoke it by passing an array. For example, printArray method to display 3, 1, 2, 6, 4, and 2 :
printArray(new int[]{3, 1, 2, 6, 4, 2});click below button to copy the code. By - java tutorial - team
Returning an Array from a Method
- A method may also return an array. For example, the following method returns an array that is the reversal of another array :
public static int[] reverse(int[] list) {
int[] result = new int[list.length];
for (int i = 0, j = result.length - 1; i < list.length; i++, j--) {
result[j] = list[i];
}
return result;
}click below button to copy the code. By - java tutorial - team
Methods for an array
The java.util.Array class takes several static methods for sorting and searching arrays, comparing arrays, and filling array elements.
| Sr.No. | Method & Description |
|---|---|
| 1 | public static int binarySearch(Object[] a, Object key) Using the binary search algorithm it can searches the specified array Object ( Byte, Int , double, etc.).if it is contained in the list it returns index of the search key,otherwise, it returns ( – (insertion point + 1)). |
| 2 | public static boolean equals(long[] a, long[] a2) Two arrays are considered equivalent if both arrays contain the same number of elements, and all corresponding pairs of elements in the two arrays are same this returns true. |
| 3 | public static void fill(int[] a, int val) It Assigns the specified array of value to Int. |
| 4 | public static void sort(Object[] a) Sorts the specified array of objects into an ascending order,the same method could be used by all other primitive data types ( Byte, short, Int, etc.) |
Example 1: length of the array
public class Test {
public static void main (String [] args) {
// Array of myArray1 from 5 elements of type double.
double [] myArray1 = {2.4, 3.8, 11.2, 9.8, 1.18};
// Output the length of the array myArray1 to the screen.
System.out.println ("The number of elements in the array myArray1:" + myArray1.length);
// The array myArray2 from 4 elements of type String.
String [] myArray2 = {"Java", "array", "Example", "wikitechy.com"};
// Display the size of myArray2 array on the screen.
System.out.println ("The number of elements in the array myArray2:" + myArray2.length);
}
}click below button to copy the code. By - java tutorial - team
Output
The number of elements in the array myArray1: 5
The number of elements in the array myArray2: 4Example 2: the maximum element of an array
- Simple ways to find the maximum number in an array in Java. First, use the Math.max () method .
public class Test {
public static void main (String [] args) {
// Find the maximum element in the array myArray from 4 elements of type double.
double [] myArray = {11, 5.8, 11.1, 10.9};
// Set the max variable to the minimum double-value.
double max = Double.MIN_VALUE;
// Find all the elements of the array.
for (int i = 0; i <myArray.length; i ++) {
// Variable max with the method Math.max () assign the maximum value
// by selecting the largest of the two values (the "old" value of max and the value of the element).
max = Math.max (max, myArray [i]);
}
// Display the largest number of myArray arrays on the screen.
System.out.println ("The maximum element in the array myArray:" + max);
}
}click below button to copy the code. By - java tutorial - team
Output
The maximum element in the array myArray: 11.1