AbstractList indexOf() method in Java with Examples
Last Updated :
26 Nov, 2018
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The indexOf() method of java.util.AbstractList 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:
Java
Java
Java
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. Below are the examples to illustrate the indexOf() method. Example 1:
// Java program to demonstrate
// indexOf() method
// for Integer value
import java.util.*;
public class GFG1 {
public static void main(String[] argv)
throws Exception
{
try {
// Creating object of AbstractList<Integer>
AbstractList<Integer>
arrlist1 = new ArrayList<Integer>();
// Populating arrlist1
arrlist1.add(10);
arrlist1.add(20);
arrlist1.add(30);
arrlist1.add(40);
arrlist1.add(50);
// print arrlist1
System.out.println("ArrayListlist : "
+ arrlist1);
// getting the index of element 30
// using indexOf() method
int index = arrlist1.indexOf(30);
// print the index
System.out.println("index : " + index);
}
catch (NullPointerException e) {
System.out.println("Exception thrown : " + e);
}
}
}
Output:
Example 2:
ArrayListlist : [10, 20, 30, 40, 50] index : 2
// Java program to demonstrate
// indexOf() method
// for Integer value
import java.util.*;
public class GFG1 {
public static void main(String[] argv)
throws Exception
{
try {
// Creating object of AbstractList<Integer>
AbstractList<Integer>
arrlist1 = new ArrayList<Integer>();
// Populating arrlist1
arrlist1.add(10);
arrlist1.add(20);
arrlist1.add(30);
arrlist1.add(40);
arrlist1.add(50);
// print arrlist1
System.out.println("ArrayListlist : "
+ arrlist1);
// getting the index of element 25
// using indexOf() method
int index = arrlist1.indexOf(25);
// print the index
System.out.println("Index of 25 : "
+ index);
}
catch (NullPointerException e) {
System.out.println("Exception thrown : " + e);
}
}
}
Output:
Example 3: For Null value
ArrayListlist : [10, 20, 30, 40, 50] Index of 25 : -1
// Java program to demonstrate
// indexOf() method
// for null value
import java.util.*;
public class GFG1 {
public static void main(String[] argv) throws Exception
{
try {
// Creating object of AbstractList<Integer>
AbstractList<Integer>
arrlist1 = new ArrayList<Integer>();
// Populating arrlist1
arrlist1.add(10);
arrlist1.add(20);
arrlist1.add(30);
arrlist1.add(40);
arrlist1.add(50);
// print arrlist1
System.out.println("ArrayListlist : "
+ arrlist1);
// creating null object
Object value = null;
// getting the index of element null
// using indexOf() method
int index = arrlist1.indexOf(value);
// print the index
System.out.println("Index of null : "
+ index);
}
catch (NullPointerException e) {
System.out.println("Exception thrown : " + e);
}
}
}
Output:
ArrayListlist : [10, 20, 30, 40, 50] Index of null : -1
