Java defines several types of exceptions that relate to its various class libraries. Java also allows users to define their own exceptions.
exceptions-in-java
Built-in Exceptions
Built-in exceptions are the exceptions which 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.
ArithmeticException
It is thrown when an exceptional condition has occurred in an arithmetic operation.
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.
ClassNotFoundException
This Exception is raised when we try to access a class whose definition is not found
FileNotFoundException
This Exception is raised when a file is not accessible or does not open.
IOException
It is thrown when an input-output operation failed or interrupted
InterruptedException
It is thrown when a thread is waiting , sleeping , or doing some processing , and it is interrupted.
NoSuchFieldException
It is thrown when a class does not contain the field (or variable) specified
NoSuchMethodException
It is thrown when accessing a method which is not found.
NullPointerException
This exception is raised when referring to the members of a null object. Null represents nothing
NumberFormatException
This exception is raised when a method could not convert a string into a numeric format.
RuntimeException
This represents any exception which occurs during runtime.
StringIndexOutOfBoundsException
It is thrown by String class methods to indicate that an index is either negative or greater than the size of the string
Examples of Built-in Exception:
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
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..
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
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
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
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
User-Defined Exceptions
Sometimes, the built-in exceptions in Java are not able to describe a certain situation. In such cases, user can also create exceptions which are called ‘user-defined Exceptions’.
Following steps are followed for the creation of user-defined Exception.
The user should create an exception class as a subclass of Exception class. Since all the exceptions are subclasses of 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 super class(Exception) constructor from this and send the string there.
MyException(String str)
{
super(str);
}
To raise exception of user-defined type, we need to create an object to his exception class and throw it using throw clause, as:
MyException me = new MyException(“Exception details”);
throw me;
The following program illustrates how to create 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, 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”.
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[] =
{"Rish", "Nishu", "Sush", "Alice", "Akash"};
private static double bal[] =
{10000.00, 12000.00, 5600.0, 999.00, 1100.55};
// default constructor
MyException() { }
// parametrized 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 Rish 10000.0
1002 Nishu 12000.0
1003 Bob 5600.0
1004 Alice 999.0