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Showing content from https://www.geeksforgeeks.org/java/list-indexof-method-in-java-with-examples/ below:

List indexOf() Method in Java with Examples

Last Updated : 29 Nov, 2024

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


 // 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"));      	
    }
}

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


 // 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));
    }
}

Program 2:

Below is the code to show implementation of list.hashCode() using Linkedlist.

Java


 // 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"));
    }
}

Reference: Oracle Docs

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