Example of the ArrayList method indexOf()

The indexOf() of the ArrayList class is used to find the position of the first occurrence of a specific element in the ArrayList in Java.

public int indexOf(Object o): This method returns the index of the first occurrence of the object o, otherwise -1 if the specified item does not exist in the list.

import java.util.ArrayList; 

public class ArrayListIndexOfFirst{ 
 
 public static void main(String[] args) {
 
 // Create an ArrayList< String> 
 ArrayList< String> arraylist = new ArrayList< String> (); 
 
 //add strings to ArrayList
 arraylist.add("e1"); 
 arraylist.add("e2"); 
 arraylist.add("e1"); 
 arraylist.add("e3"); 
 arraylist.add("e4"); 
 
 System.out.println("first occurrence of e1: "+arraylist.indexOf("e1")); 
 System.out.println("first occurrence of e3: "+arraylist.indexOf("e3")); 
 }
}

Runtime:

first occurrence of e1:0
first occurrence of e3:3

References:
Java.util.ArrayList.indexOf() Method