List indexOf() Method in Java with Examples
Last Updated :
29 Nov, 2024
Improve
This method returns the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element.
Example:
// Java Program to Implement List
// indexOf() Method
import java.util.*;
class GFG
{
public static void main (String[] args)
{
// List Created
List<String> l = new ArrayList<String>();
// Adding Elements
l.add("Geeks");
l.add("for Geeks");
l.add("GFG");
// Index Of
System.out.println("Index of GFG is " + l.indexOf("GFG"));
}
}
Output
Index of GFG is 2
Syntax of Method
public int indexOf(Object o)
Parameters: This function has a single parameter, i.e, the element to be searched in the list.
Returns: This method returns the index of first occurrence of the given element in the list and returns "-1" if element is not in the list.
Example of List indexOf() Method
Below programs show the implementation of this method.
Program 1:
// Java code to show the implementation of
// indexOf method in list interface
import java.util.*;
public class GfG
{
public static void main(String[] args)
{
// Initializing a list of type Linkedlist
List<Integer> l = new LinkedList<>();
// Adding elements in List
l.add(1);
l.add(3);
l.add(5);
l.add(7);
System.out.println(l);
// Index Of
System.out.println(l.indexOf(5));
}
}
Output
[1, 3, 5, 7] 2
Program 2:
Below is the code to show implementation of list.hashCode() using Linkedlist.
// Java code to show the implementation of
// indexOf method in list interface
import java.util.*;
public class GfG
{
public static void main(String[] args)
{
// Initializing a list of type Linkedlist
List<String> l = new LinkedList<>();
l.add("10");
l.add("15");
l.add("20");
System.out.println(l);
System.out.println(l.indexOf("20"));
}
}
Output
[10, 15, 20] 2
Reference: Oracle Docs
