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Java ArrayList indexOf() Method with Example

ArrayList Class indexOf() method: Here, we are going to learn about the indexOf() method of ArrayList Class with its syntax and example.
Submitted by Preeti Jain, on January 18, 2020

ArrayList Class indexOf() method

• indexOf() method is available in java.util package.
• indexOf() method is used to return the index of the first occurrence of the given object.
• indexOf() method is a non-static method so it is accessible with the class object and if we try to access the method with the class name then we will get an error.

Syntax:

     public int indexOf(Object obj);

Parameter(s):

• Object obj – represents the object to search for the index in this Arraylist.

Return value:

The return type of the method is int, it returns the index of the first occurrence of the given object otherwise, it returns -1 when the given object does not exist in this Arraylist.

Example:

// Java program to demonstrate the example 
// of int indexOf(int) method of ArrayList.

import java.util.*;

public class IndexOfArrayList {
    public static void main(String[] args) {
        // Create an ArrayList with initial 
        // capacity of storing elements

        ArrayList < String > arr_l = new ArrayList < String > (10);

        // By using add() method is to add 
        // elements in this ArrayList
        arr_l.add("C");
        arr_l.add("C++");
        arr_l.add("JAVA");
        arr_l.add("DOTNET");
        arr_l.add("PHP");

        // Display ArrayList
        System.out.println("ArrayList Elements :" + arr_l);

        // By using indexOf(Object) method is to
        // return the index of the first occurrence
        // of the given Object in this ArrayList
        int index = arr_l.indexOf("JAVA");

        // Display Index 
        System.out.println("arr_l.indexOf(JAVA) : " + index);
    }
}

Output

ArrayList Elements :[C, C++, JAVA, DOTNET, PHP]
arr_l.indexOf(JAVA) : 2