Java List indexOf() Method

The indexOf() method of List interface returns the index of the first occurrence of the specified element in this list. It returns -1 if the specified element is not present in this list.

Syntax

Parameters

The parameter 'o' represents the element to be searched.

Throws:

ClassCastException- If the type of the specified element is not compatible with this list.

NullPointerException- If the specified element is null and this list does not allow null elements.

Return

The indexOf() method returns the index of the first occurrence of the specified element if it is present in this list, else it returns -1.

Example 1

import java.util.LinkedList;
import java.util.List;
public class JavaListIndexOfExample1 {
public static void main(String[] args) {
        List<Integer> list= new LinkedList<>();
for (int i=0;i<6;i++){
list.add(i);
// returns the element at the specified position in this list
int value =list.indexOf(i);
System.out.println("Element stored at index "+i+" : "+value);
        }
    }
}

Test it Now

Output:

Element stored at index 0 : 0
Element stored at index 1 : 1
Element stored at index 2 : 2
Element stored at index 3 : 3
Element stored at index 4 : 4
Element stored at index 5 : 5

Example 2

import java.util.LinkedList;
import java.util.List;
public class JavaListIndexOfExample2 {
public static void main(String[] args) {
        List<Integer> list= new LinkedList<>();
list.add(null);
list.add(null);
list.add(null);
// returns -1 if the no value is present in the specified index
int value =list.indexOf(90);
System.out.println("Element stored at Index "+90+" : "+value);
    }
}

Test it Now

Output:

Element stored at Index 90 : -1

Example 3

import java.util.LinkedList;
import java.util.List;
public class JavaListIndexOfExample3 {
public static void main(String[] args) {
        List<Integer> list= new LinkedList<>();
list.add(67);
list.add(89);
// returns -1 if the no value is present in the specified index
int value =list.indexOf(null);
System.out.println("Element stored at "+null+" : "+value);
    }
}

Test it Now

Output: