What is the LinkedList.indexOf method in Java?

The indexOf method of the LinkedList class can be used to get the index of the first occurrence of the specified element in the linked list.

A linked list is a collection of linear data elements. Each element, or node, contains data and reference parts.

Syntax

public int indexOf(Object obj);

Parameter

obj: The element to be searched in the list as an argument.

Return value

This method returns the first index at which the specified element is present in the list.

If the element is not present in the list, then -1 is returned.

Code

The code below demonstrates how to use the indexOf method.

import java.util.LinkedList;
class LinkedListIndexOfExample {
    public static void main( String args[] ) {
      LinkedList<String> list = new LinkedList<>();
      list.add("1");
      list.add("2");
      list.add("1");
      System.out.println("The list is " + list);
      System.out.println("First Index of element '1' is : " + list.indexOf("1"));
      System.out.println("First Index of element '2' is : " + list.indexOf("2"));
      System.out.println("First Index of element '3' is : " + list.indexOf("3"));
    }
}

Explanation

In the above code:

In line number 1, we import the LinkedList class.

import java.util.LinkedList;

In line number 4, we create a LinkedList object with the name list.

LinkedList<String> list = new LinkedList<>();

From line number 5 to 7, we use the add method of the list object to add three elements ("1","2","3") to the list.

list.add("1");
list.add("2");
list.add("1");

In line number 10, we use the indexOf method of the list object to get the index of the first occurrence of the element "1". The element "1" is present at two indices: 0 and 2. We get 0 as result since that is the first occurrence.

list.indexOf("1"); // 0

In line number 11, we use the indexOf method of the list object to get the index of the first occurrence of the element "2". The element "2" is present only at index 1, so it is returned.

list.indexOf("2"); // 1

In line number 12, we use the indexOf method of the list object to get the index of the first occurrence of the element "3". The element "3" is not present in the list, so -1 is returned.

list.indexOf("3"); // -1

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