Application of Java Array indexof Method
- The indexof functions are most helpful for finding the last or first occurrence of events.
- For example, last time the number 1 appears in a die throw or the first time any letter appears in a name.
How to Get an Index of an Array Element in Java?
Linear search
In Java, you can perform a linear search on an array to find the index of a particular element by iterating through the array and comparing each element to the target element. Given implementation will hep you understand the Linear search:
public class Main {
static int [] arr;
public static void main(String[] args) {
arr = new int[]{3,2,4,5,6,7};
// Function call and the return value stored in 'i'
int i = find_index(arr, 6);
if(i == -1)
{
System.out.print("Element not contained by the array");
}
else
System.out.print("Element found at : "+i);
}
private static int find_index(int [] arr,int j)
{
for(int i=0;i<arr.length;i++)
{
// comparing element to the target element
if(arr[i]==j)
{
return i;
}
}
return -1;
}
}
Output:
Element found at : 4
Time complexity: O(n)
indexOf() method
In Java, the indexOf method of the Arrays class to find the index of a particular element in an array. The indexOf method returns index of the element first occurring in the array, or -1 if the element is not found.
Implementation:
import java.util.Arrays;
public class IndexOf {
public static void main(String[] args) {
Integer[] array1 = {2, 4, 6, 8, 10};
int index = Arrays.asList(array1).indexOf(8);
System.out.println("Found element at location at index:"+index);
}
}
Output:
Found element at location at index:3
Time complexity:O(n)
binarySearch() method
In Java, you can use the binarySearch method of the Arrays class to perform a binary search on a sorted array and find the index of a particular element. It returns the index of the element the array, or a negative number if the element is not found.
Implementation:
import java.util.Arrays;
public class Main {
public static void main(String[] args) {
char arr[] = {1,25, 67,89};
char search = 25;
int result = Arrays.binarySearch(arr, search);
System.out.println("Element is at index: " + result);
}
}
Output:
Element is at index: 1
Time complexity: O(log n)
Also see, Swap Function in Java
Code to Demonstrate Java Array Indexof Method
import java.util.ArrayList;
public class IndexOfEx {
public static void main(String[] args) {
ArrayList<Integer> ar = new ArrayList<Integer>(4);
/* initializing values */
ar.add(10);
ar.add(20);
ar.add(30);
ar.add(40);
System.out.print("The ArrayList contains : \n");
for (Integer x : ar) {
System.out.print(x);
System.out.print(" ");
}
/* Java Array indexOf() method to find index of 40 */
int pos = ar.indexOf(40);
System.out.println("\nThe element 40 is at index : " + pos);
}
}

You can also try this code with Online Java Compiler
Run Code
Output
The ArrayList contains :
10 20 30 40
The element 40 is at index : 3

You can also try this code with Online Java Compiler
Run Code
Try it on online java compiler.
Frequently Asked Questions
What is the Java array Indexof method?
We create an array of integers and then use Arrays.asList() to convert it into a list so that we can access the indexOf() function. The indexOf() method of ArrayList returns -1 if the element is not present in this list or the index of the first instance of the element in the list.
What is the application of the Java array Indexof method?
The indexof functions are most helpful for finding the last or first occurrence of events, such as the last time the number 1 appears in a die throw or the first time any letter appears in a name.
Can you use indexOf on an array in Java?
Java doesn't have an indexOf() method for arrays, but it does have one for ArrayLists, which returns the index of the specified element. We first create an array of integers and then use Arrays.asList() to convert it into a list so that we can access the indexOf() function.
How to display array index in Java?
The three methods to determine the index of an element in Java are linear search which follows the process of iterating and comparing, and indexOf, which is a built-in method. And binary search, which is a sorted array search.
Conclusion
In this article, we have discussed Java Array indexof method in detail. We have also seen an example to get a clear understanding of this topic.
If you want to learn more, check out our articles on Java Tokens, Why To Use Web2py?, Postbacks and Internationalization in web2py, Third Party Modules In Web2py, and Java Verify.
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