AbstractList indexOf() method in Java with Examples

Last Updated : 11 Jul, 2025
The indexOf() method of java.util.AbstractList class is used to return the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element. More formally, returns the lowest index i such that (o==null ? get(i)==null : o.equals(get(i))), or -1 if there is no such index. Syntax: 
public int indexOf(Object o)
Parameters: This method takes Object o as parameter which is the element to search for. Return Value: 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. Below are the examples to illustrate the indexOf() method. Example 1: Java
// Java program to demonstrate
// indexOf() method
// for Integer value

import java.util.*;

public class GFG1 {
    public static void main(String[] argv)
        throws Exception
    {

        try {

            // Creating object of AbstractList<Integer>
            AbstractList<Integer>
                arrlist1 = new ArrayList<Integer>();

            // Populating arrlist1
            arrlist1.add(10);
            arrlist1.add(20);
            arrlist1.add(30);
            arrlist1.add(40);
            arrlist1.add(50);

            // print arrlist1
            System.out.println("ArrayListlist : "
                               + arrlist1);

            // getting the index of element 30
            // using indexOf() method
            int index = arrlist1.indexOf(30);

            // print the index
            System.out.println("noindex : " + index);
        }

        catch (NullPointerException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}
Output: 
ArrayListlist : [10, 20, 30, 40, 50]
index : 2
Example 2: Java
// Java program to demonstrate
// indexOf() method
// for Integer value

import java.util.*;

public class GFG1 {
    public static void main(String[] argv)
        throws Exception
    {

        try {

            // Creating object of AbstractList<Integer>
            AbstractList<Integer>
                arrlist1 = new ArrayList<Integer>();

            // Populating arrlist1
            arrlist1.add(10);
            arrlist1.add(20);
            arrlist1.add(30);
            arrlist1.add(40);
            arrlist1.add(50);

            // print arrlist1
            System.out.println("ArrayListlist : "
                               + arrlist1);

            // getting the index of element 25
            // using indexOf() method
            int index = arrlist1.indexOf(25);

            // print the index
            System.out.println("Index of 25 : "
                               + index);
        }

        catch (NullPointerException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}
Output: 
ArrayListlist : [10, 20, 30, 40, 50]
Index of 25 : -1
Example 3: For Null value Java
// Java program to demonstrate
// indexOf() method
// for null value

import java.util.*;

public class GFG1 {
    public static void main(String[] argv) throws Exception
    {
        try {

            // Creating object of AbstractList<Integer>
            AbstractList<Integer>
                arrlist1 = new ArrayList<Integer>();

            // Populating arrlist1
            arrlist1.add(10);
            arrlist1.add(20);
            arrlist1.add(30);
            arrlist1.add(40);
            arrlist1.add(50);

            // print arrlist1
            System.out.println("ArrayListlist : "
                               + arrlist1);

            // creating null object
            Object value = null;

            // getting the index of element null
            // using indexOf() method
            int index = arrlist1.indexOf(value);

            // print the index
            System.out.println("Index of null : "
                               + index);
        }

        catch (NullPointerException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}
Output: 
ArrayListlist : [10, 20, 30, 40, 50]
Index of null : -1
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