AbstractSequentialList indexOf() method in Java with Example

The indexOf() method of java.util.AbstractSequentialList class is used to return the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element. More formally, returns the lowest index i such that (o==null ? get(i)==null : o.equals(get(i))), or -1 if there is no such index.

Syntax:

public int indexOf(Object o)

Parameters: This method takes Object o as parameter which is the element to search for.

Return Value: This method returns the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element.

Exception: This method throws:

• 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.

Below are the examples to illustrate the indexOf() method.

Example 1:

// Java program to demonstrate indexOf()
// method for AbstractSequentialList

import java.util.*;

public class GFG {
    public static void main(String[] args)
    {

        // Creating object of AbstractSequentialList
        AbstractSequentialList<Integer>
            arrlist1 = new LinkedList<Integer>();

        // Populating arrlist1
        arrlist1.add(10);
        arrlist1.add(20);
        arrlist1.add(30);
        arrlist1.add(40);
        arrlist1.add(50);

        // print arrlist1
        System.out.println("AbstractSequentialList: "
                           + arrlist1);

        // getting the index of element 30
        // using indexOf() method
        int index = arrlist1.indexOf(30);

        // print the index
        System.out.println("Index of 30: "
                           + index);
    }
}

Output:

AbstractSequentialList: [10, 20, 30, 40, 50]
Index of 30: 2

Example 2:

// Java program to demonstrate indexOf()
// method for AbstractSequentialList

import java.util.*;

public class GFG1 {
    public static void main(String[] args)
    {
        // Creating object of AbstractSequentialList
        AbstractSequentialList<Integer>
            arrlist1 = new LinkedList<Integer>();

        // Populating arrlist1
        arrlist1.add(10);
        arrlist1.add(20);
        arrlist1.add(30);
        arrlist1.add(40);
        arrlist1.add(50);

        // print arrlist1
        System.out.println("LinkedListlist: "
                           + arrlist1);

        // getting the index of element 100
        // using indexOf() method
        int index = arrlist1.indexOf(null);

        // print the index
        System.out.println("Index of 100: "
                           + index);
    }
}

Output:

LinkedListlist: [10, 20, 30, 40, 50]
Index of 100: -1