Types of Exception in Java with Examples

Java defines several types of exceptions that relate to its various class libraries. Java also allows users to define their own exceptions. 

Built-in Exceptions:

Built-in exceptions are the exceptions that are available in Java libraries. These exceptions are suitable to explain certain error situations. Below is the list of important built-in exceptions in Java. 

1. ArithmeticException: It is thrown when an exceptional condition has occurred in an arithmetic operation.
2. ArrayIndexOutOfBoundsException: It is thrown to indicate that an array has been accessed with an illegal index. The index is either negative or greater than or equal to the size of the array.
3. ClassNotFoundException: This Exception is raised when we try to access a class whose definition is not found
4. FileNotFoundException: This Exception is raised when a file is not accessible or does not open.
5. IOException: It is thrown when an input-output operation failed or interrupted
6. InterruptedException: It is thrown when a thread is waiting, sleeping, or doing some processing, and it is interrupted.
7. NoSuchFieldException: It is thrown when a class does not contain the field (or variable) specified
8. NoSuchMethodException: It is thrown when accessing a method that is not found.
9. NullPointerException: This exception is raised when referring to the members of a null object. Null represents nothing
10. NumberFormatException: This exception is raised when a method could not convert a string into a numeric format.
11. RuntimeException: This represents an exception that occurs during runtime.
12. StringIndexOutOfBoundsException: It is thrown by String class methods to indicate that an index is either negative or greater than the size of the string
13. IllegalArgumentException : This exception will throw the error or error statement when the method receives an argument which is not accurately fit to the given relation or condition. It comes under the unchecked exception. 
14. IllegalStateException : This exception will throw an error or error message when the method is not accessed for the particular operation in the application. It comes under the unchecked exception.

Examples of Built-in Exception

A. Arithmetic exception

Java

// Java program to demonstrate ArithmeticException
class ArithmeticException_Demo
{
    public static void main(String args[])
    {
        try {
            int a = 30, b = 0;
            int c = a/b;  // cannot divide by zero
            System.out.println ("Result = " + c);
        }
        catch(ArithmeticException e) {
            System.out.println ("Can't divide a number by 0");
        }
    }
}

Output

Can't divide a number by 0

B. NullPointer Exception

Java

//Java program to demonstrate NullPointerException
class NullPointer_Demo
{
    public static void main(String args[])
    {
        try {
            String a = null; //null value
            System.out.println(a.charAt(0));
        } catch(NullPointerException e) {
            System.out.println("NullPointerException..");
        }
    }
}

Output

NullPointerException..

C. StringIndexOutOfBound Exception

Java

// Java program to demonstrate StringIndexOutOfBoundsException
class StringIndexOutOfBound_Demo
{
    public static void main(String args[])
    {
        try {
            String a = "This is like chipping "; // length is 22
            char c = a.charAt(24); // accessing 25th element
            System.out.println(c);
        }
        catch(StringIndexOutOfBoundsException e) {
            System.out.println("StringIndexOutOfBoundsException");
        }
    }
}

Output

StringIndexOutOfBoundsException

D. FileNotFound Exception

Java

//Java program to demonstrate FileNotFoundException
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
 class File_notFound_Demo {

    public static void main(String args[])  {
        try {

            // Following file does not exist
            File file = new File("E://file.txt");

            FileReader fr = new FileReader(file);
        } catch (FileNotFoundException e) {
           System.out.println("File does not exist");
        }
    }
}

Output:

File does not exist

E. NumberFormat Exception

Java

// Java program to demonstrate NumberFormatException
class  NumberFormat_Demo
{
    public static void main(String args[])
    {
        try {
            // "akki" is not a number
            int num = Integer.parseInt ("akki") ;

            System.out.println(num);
        } catch(NumberFormatException e) {
            System.out.println("Number format exception");
        }
    }
}

Output

Number format exception

F. ArrayIndexOutOfBounds Exception

Java

// Java program to demonstrate ArrayIndexOutOfBoundException
class ArrayIndexOutOfBound_Demo
{
    public static void main(String args[])
    {
        try{
            int a[] = new int[5];
            a[6] = 9; // accessing 7th element in an array of
                      // size 5
        }
        catch(ArrayIndexOutOfBoundsException e){
            System.out.println ("Array Index is Out Of Bounds");
        }
    }
}

Output

Array Index is Out Of Bounds

G. IO Exception 

Java

// Java program to demonstrate IOException
class IOException_Demo {

    public static void main(String[] args)
    {

        // Create a new scanner with the specified String
        // Object
        Scanner scan = new Scanner("Hello Geek!");

        // Print the line
        System.out.println("" + scan.nextLine());

        // Check if there is an IO exception
        System.out.println("Exception Output: "
                           + scan.ioException());

        scan.close();
    }
}

Output:

Hello Geek! 
Exception Output: null

H. NoSuchMethod Exception 

Java

// Java program to demonstrate NoSuchElementException
public class NoSuchElementException_Demo {

    public static void main(String[] args)
    {

        Set exampleleSet = new HashSet();

        Hashtable exampleTable = new Hashtable();

        exampleleSet.iterator().next();
          //accessing Set

        exampleTable.elements().nextElement();
          //accessing Hashtable

          // This throws a NoSuchElementException as there are
        // no elements in Set and HashTable and we are
        // trying to access elements
    }
}

I. IllegalArgumentException: This program, checks whether the person is eligible for voting or not. If the age is greater than or equal to 18 then it will not throw any error. If the age is less than 18 then it will throw an error with the error statement. 

Also, we can specify “throw new IllegalArgumentException()” without the error message. We can also specify Integer.toString(variable_name) inside the IllegalArgumentException() and It will print the argument name which is not satisfied the given condition.

Java

/*package whatever //do not write package name here */

import java.io.*;

class GFG {
   public static void print(int a)
    {
         if(a>=18){
          System.out.println("Eligible for Voting");
          }
          else{

          throw new IllegalArgumentException("Not Eligible for Voting");

          }

    }
    public static void main(String[] args) {
         GFG.print(14);
    }
}

Output : 

Exception in thread "main" java.lang.IllegalArgumentException: Not Eligible for Voting
at GFG.print(File.java:13)
at GFG.main(File.java:19)

J. IllegalStateException: This program, displays the addition of numbers only for Positive integers. If both the numbers are positive then only it will call the print method to print the result otherwise it will throw the IllegalStateException with an error statement. Here, the method is not accessible for non-positive integers.

Also, we can specify the “throw new IllegalStateException()” without the error statement.

Java

/*package whatever //do not write package name here */

import java.io.*;

class GFG {
      public static void  print(int a,int b)
     {
         System.out.println("Addition of Positive Integers :"+(a+b));
     }

    public static void main(String[] args) {
    int n1=7;
    int n2=-3;
     if(n1>=0 && n2>=0)
     {
         GFG.print(n1,n2);
     }
     else
     {
         throw new IllegalStateException("Either one or two numbers are not Positive Integer");
     }
    }
}

Output :

Exception in thread "main" java.lang.IllegalStateException: Either one or two numbers are not Positive Integer
at GFG.main(File.java:20)

k. ClassNotFound Exception :

Java

// Java program to demonstrate ClassNotFoundException
public class ClassNotFoundException_Demo
{
    public static void main(String[] args) {
        try{
            Class.forName("Class1");   // Class1 is not defined
        }
        catch(ClassNotFoundException e){
            System.out.println(e);
            System.out.println("Class Not Found...");
        }
    }
}

Output

java.lang.ClassNotFoundException: Class1
Class Not Found...

User-Defined Exceptions

Sometimes, the built-in exceptions in Java are not able to describe a certain situation. In such cases, the user can also create exceptions which are called ‘user-defined Exceptions’. 

The following steps are followed for the creation of a user-defined Exception. 

• The user should create an exception class as a subclass of the Exception class. Since all the exceptions are subclasses of the Exception class, the user should also make his class a subclass of it. This is done as: 

class MyException extends Exception

• We can write a default constructor in his own exception class. 

MyException(){}

• We can also create a parameterized constructor with a string as a parameter. 
  We can use this to store exception details. We can call the superclass(Exception) constructor from this and send the string there. 

MyException(String str)
{
   super(str);
}

• To raise an exception of a user-defined type, we need to create an object to his exception class and throw it using the throw clause, as: 

MyException me = new MyException(“Exception details”);
throw me;

• The following program illustrates how to create your own exception class MyException.
• Details of account numbers, customer names, and balance amounts are taken in the form of three arrays.
• In main() method, the details are displayed using a for-loop. At this time, a check is done if in any account the balance amount is less than the minimum balance amount to be apt in the account.
• If it is so, then MyException is raised and a message is displayed “Balance amount is less”.

Example

Java

// Java program to demonstrate user defined exception

// This program throws an exception whenever balance
// amount is below Rs 1000
class MyException extends Exception
{
    //store account information
    private static int accno[] = {1001, 1002, 1003, 1004};

    private static String name[] =
                 {"Nish", "Shubh", "Sush", "Abhi", "Akash"};

    private static double bal[] =
         {10000.00, 12000.00, 5600.0, 999.00, 1100.55};

    // default constructor
    MyException() {    }

    // parameterized constructor
    MyException(String str) { super(str); }

    // write main()
    public static void main(String[] args)
    {
        try  {
            // display the heading for the table
            System.out.println("ACCNO" + "\t" + "CUSTOMER" +
                                           "\t" + "BALANCE");

            // display the actual account information
            for (int i = 0; i < 5 ; i++)
            {
                System.out.println(accno[i] + "\t" + name[i] +
                                               "\t" + bal[i]);

                // display own exception if balance < 1000
                if (bal[i] < 1000)
                {
                    MyException me =
                       new MyException("Balance is less than 1000");
                    throw me;
                }
            }
        } //end of try

        catch (MyException e) {
            e.printStackTrace();
        }
    }
}

Runtime Error 

 MyException: Balance is less than 1000
    at MyException.main(fileProperty.java:36)

Output:

ACCNO    CUSTOMER    BALANCE
1001    Nish    10000.0
1002    Shubh    12000.0
1003    Sush    5600.0
1004    Abhi    999.0