Java ArrayList - indexOf() Method

The java.util.ArrayList.indexOf() method returns index of the first occurrence of the specified element in this ArrayList. It returns -1 if element is not present in the ArrayList.

Syntax

public int indexOf(Object o)

Parameters

Return Value

Returns the index of the first occurrence of the specified element in the ArrayList, or -1 if element is not present in the ArrayList.

Exception

NA.

Example:

In the example below, the java.util.ArrayList.indexOf() method is used to find the index of first occurrence of the specified element in the ArrayList MyList.

import java.util.*;

public class MyClass {
  public static void main(String[] args) {
    //creating a ArrayList
    ArrayList<Integer> MyList = new ArrayList<Integer>();

    //populating ArrayList
    MyList.add(10);
    MyList.add(30);
    MyList.add(20);
    MyList.add(50);
    MyList.add(30);

    System.out.print("30 appeared first time at index=" + MyList.indexOf(30)); 
  }
}

The output of the above code will be:

30 appeared first time at index=1