Java exceptions

Exceptions are used to handle situations where something unexpected might happen, such as attempting to divide by zero, a file you're trying to access is not found, and more.

This tutorial focuses on:

The various Java exceptions
The try-catch block
The try-catch-finally block

The various Java exceptions

Java has classes that can be used to handle exceptions in various situations.

ArithmeticException - Used to handle arithmetic errors such as attempting to divide a number by zero. Located in the java.lang package.
NoSuchMethodException - Used to handle a situation where a method is not found. Located in the java.lang package.
IOException - Used to handle input/output errors. Located in the java.io package.
FileNotFoundException - Used to handle a situation where a file cannot be found. Located in the java.io package.

NOTE: The base class of all the exception classes is the class Exception and it is located in the java.lang package.

The try-catch block

The way to deal with exceptions is to use a try-catch block. The try-catch block will execute one set of code if an exception does not occur, and a different set of code if an exception does occur. Specify within the try-catch block which exception it is you are watching for.

Syntax:

try{ code to execute if exception doesn't occur; } catch(anExceptionThatMayOccur){ code to execute if exception does occur; }

Example:

try{ name = reader.readLine(); System.out.println("Your name is " + name); } //watch for an input/output exception catch(IOException ioe){ System.out.println("An unexpected error has occured"); }

The try-catch-finally block

The try-catch-finally block is the same as the try-catch block with one addition. The try-catch-finally block contains a set of code that will execute whether an exception occured or not.

Syntax:

try{ code to execute if exception doesn't occur; } catch(anExceptionThatMayOccur){ code to execute if exception does occur; } finally{ code to execute whether exception occurs or not; }

Example:

try{ name = reader.readLine(); System.out.println("Your name is " + name); } //watch for an input/output exception catch(IOException ioe){ System.out.println("An unexpected error has occured"); } finally{ //print this whether an exception occurs or not System.out.println("Thanks for stopping by!); }