$show=/label

Java ArrayList indexOf() Example to find the Object exists in List or Not

SHARE:

A quick practical example guide to find the given object is present in the list or not. ArrayList has indexOf(Object o) which checks and returns the index of the found element.

1. Introduction


In this article, We will learn the ArrayList class indexOf() method. Let us take a look into how to find the value or object that is present in the list or not. And also what are the valid arguments to pass and what are the exceptions will be thrown at run time exception.

String class also has indexOf() method

Java ArrayList indexOf() Example to find the Object exists in List or Not





2. int indexOf(Object o)


indexOf() method is used to get the index of the given object. If the given object exists in the list it returns the index of the particular value. If the value is not present then it returns -1 always negative value. If the given value is present multiple times in the list then it takes the first occurrence of the value and returns its index. 

indexOf(Object o) method takes Object type argument. So that means any value or object can be passed to this method. And also a null value can be passed. All these are legal to do but it throws runtime exceptions.

3. Example


Example program to check how indexOf() method returns index values. In the below program, first added String values to ArrayList and invoked the indexOf() method on the list.

package com.java.w3schools.blog.arraylist;

import java.util.ArrayList;
import java.util.List;

/**
 * 
 * Example to ArrayList indexOf() method.
 * 
 * @author javaprogramto.com
 *
 */
public class ArrayListIndexOfExample {

 public static void main(String[] args) {

  List<String> list = new ArrayList<String>();

  list.add("1");
  list.add("2");
  list.add("3");
  list.add("3");
  list.add("4");
  list.add("1");
  list.add("2");
  list.add("5");
  list.add("7");
  list.add("8");

  int index4 = list.indexOf("4");

  System.out.println("Index 4 : " + index4);

  int index3 = list.indexOf("3");

  System.out.println("Repeated value 3 index " + index3);

  int noMatch = list.indexOf("100");

  System.out.println("100 exits check : " + noMatch);

  int index8 = list.indexOf("8");
  
  System.out.println("index of value 8 is : " + index8);

 }

}

Output:

Index 4 : 4
Repeated value 3 index 2
100 exits check : -1
index of value 8 is : 9

4. Runtime Exceptions - ClassCastException, NullPointerException


If we pass the invalid values or other class objects to the indexOf() method will result in runtime exceptions saying ClassCastException or NullPointerException if null is passed.

From API:ClassCastException - if the type of the specified element is incompatible with this list
NullPointerException - if the specified element is null and this list does not permit null elements 

But, I have tried to simulate the examples for these exceptions but did not get any exceptions when passing null or different objects.

/**
 * 
 * Example to ArrayList indexOf() exception examples.
 * 
 * @author javaprogramto.com
 *
 */
public class ArrayListIndexOfExceptionExamples {

 public static void main(String[] args) {

  List<Employee> list = new ArrayList<Employee>();

  list.add(new Employee());
  list.add(new Employee());

  int indexCast = list.indexOf(new Address());

  int index = list.indexOf(null);

  System.out.println("Address indexOf : " + indexCast);
  System.out.println("null indexOf : " + index);
 }

}

class Employee {

}

class Address {

}

Output:

This program compiles and runs without any exceptions.

Address indexOf : -1
null indexOf : -1

IndexOf() on List of null values:

List<Integer> numbersList = new ArrayList<Integer>();

for (int i = 1; i <= 10; i++) {
 numbersList.add(null);

 numbersList.add(null);

 numbersList.add(null);

 numbersList.add(null);

 numbersList.add(null);
}

System.out.println("null values list size : " + numbersList.size());

int nullIndexValue = numbersList.indexOf(null);
System.out.println("null index value : " + nullIndexValue);

Output:

null values list size : 50
null index value : 0

Added 50 null values but indexOf() method returns always the first match index.

5. Conclusion


In this article, We've seen the ArrayList indexOf() method with examples. When to List indexOf() method and what are the exceptions thrown at runtime.


Read more on these topics to get a better understanding.

Object class

GitHub Code 1

GitHub Code 2

Ref

COMMENTS

BLOGGER

About Us

Author: Venkatesh - I love to learn and share the technical stuff.
Name

accumulo,1,ActiveMQ,2,Adsense,1,API,37,ArrayList,16,Arrays,7,Bean Creation,3,Bean Scopes,1,BiConsumer,1,Blogger Tips,1,Books,1,C Programming,1,Collection,5,Collections,22,Collector,1,Command Line,1,Compile Errors,1,Configurations,7,Constants,1,Control Statements,8,Conversions,6,Core Java,81,Corona India,1,Create,2,CSS,1,Date,3,Date Time API,4,Dictionary,1,Difference,1,Download,1,Eclipse,2,Efficiently,1,Error,1,Errors,1,Exception,1,Exceptions,3,Fast,1,Files,9,Float,1,Font,1,Form,1,Freshers,1,Function,3,Functional Interface,2,Garbage Collector,1,Generics,4,Git,4,Grant,1,Grep,1,HashMap,1,HomeBrew,2,HTML,2,HttpClient,2,Immutable,1,Installation,1,Interview Questions,5,Iterate,2,Jackson API,3,Java,29,Java 10,1,Java 11,5,Java 12,5,Java 13,2,Java 14,2,Java 8,66,Java 8 Difference,2,Java 8 Stream Conversions,2,java 8 Stream Examples,3,Java 9,1,Java Conversions,11,Java Design Patterns,1,Java Files,1,Java Program,2,Java Programs,65,java.lang,5,java.util. function,1,jQuery,1,Kotlin,10,Kotlin Conversions,3,Kotlin Programs,6,Lambda,1,lang,29,Leap Year,1,live updates,1,Logging,1,Mac OS,2,Math,1,Maven,1,Method References,1,Mockito,1,MongoDB,3,New Features,1,Operations,1,Optional,6,Oracle,5,Oracle 18C,1,Partition,1,Patterns,1,Programs,1,Property,1,Python,2,Quarkus,1,Read,1,Real Time,1,Recursion,2,Remove,2,Rest API,1,Schedules,1,Serialization,1,Servlet,1,Sort,1,Sorting Techniques,8,Spring,2,Spring Boot,23,Spring Email,1,Spring MVC,1,Streams,21,String,58,String Programs,9,String Revese,1,Swing,1,System,1,Tags,1,Threads,10,Tomcat,1,Tomcat 8,1,Troubleshoot,16,Unix,2,Updates,3,util,5,While Loop,1,
ltr
item
JavaProgramTo.com: Java ArrayList indexOf() Example to find the Object exists in List or Not
Java ArrayList indexOf() Example to find the Object exists in List or Not
A quick practical example guide to find the given object is present in the list or not. ArrayList has indexOf(Object o) which checks and returns the index of the found element.
https://1.bp.blogspot.com/-XBIiex2kaLo/XoS-XaRY5yI/AAAAAAAACbE/0IWIroKHsUU8tfdtOYZjca0uKkPvNqAkACLcBGAsYHQ/s640/Java%2BArrayList%2BindexOf%2528%2529%2BExample%2Bto%2Bfind%2Bthe%2BObject%2Bexists%2Bin%2BList%2Bor%2BNot.png
https://1.bp.blogspot.com/-XBIiex2kaLo/XoS-XaRY5yI/AAAAAAAACbE/0IWIroKHsUU8tfdtOYZjca0uKkPvNqAkACLcBGAsYHQ/s72-c/Java%2BArrayList%2BindexOf%2528%2529%2BExample%2Bto%2Bfind%2Bthe%2BObject%2Bexists%2Bin%2BList%2Bor%2BNot.png
JavaProgramTo.com
https://www.javaprogramto.com/2020/04/java-arraylist-indexof.html
https://www.javaprogramto.com/
https://www.javaprogramto.com/
https://www.javaprogramto.com/2020/04/java-arraylist-indexof.html
true
3124782013468838591
UTF-8
Loaded All Posts Not found any posts VIEW ALL Readmore Reply Cancel reply Delete By Home PAGES POSTS View All RECOMMENDED FOR YOU LABEL ARCHIVE SEARCH ALL POSTS Not found any post match with your request Back Home Sunday Monday Tuesday Wednesday Thursday Friday Saturday Sun Mon Tue Wed Thu Fri Sat January February March April May June July August September October November December Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec just now 1 minute ago $$1$$ minutes ago 1 hour ago $$1$$ hours ago Yesterday $$1$$ days ago $$1$$ weeks ago more than 5 weeks ago Followers Follow THIS PREMIUM CONTENT IS LOCKED STEP 1: Share to a social network STEP 2: Click the link on your social network Copy All Code Select All Code All codes were copied to your clipboard Can not copy the codes / texts, please press [CTRL]+[C] (or CMD+C with Mac) to copy Table of Content