Java Video Tutorial 6
In this part of my Java Video Tutorial I cover Java Exception handling. An exception is an object created when an error occurs.
I explain in this video the difference between run time and checked exceptions. I show you how to use try, catch and finally. We review the most common errors you will come across. I show you how to catch all and ignore individual exceptions. Yes, everything Java Exception wise will be covered.
If you missed part 1 watch it first here Java Video Tutorial.
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Code from Video
/* An exception object is created when an error occurs
* It tells you what error occurred
* Here are many of the java exceptions
*
* java.lang.RuntimeException : exceptions that can be thrown during the normal
* operation of the Java Virtual Machine. These exceptions are your responsibility
* as a programmer
*
* ArithmeticException, ArrayStoreException, BufferOverflowException,
* BufferUnderflowException, CannotRedoException, CannotUndoException,
* ClassCastException, CMMException, ConcurrentModificationException,
* DOMException, EmptyStackException, IllegalArgumentException,
* IllegalMonitorStateException, IllegalPathStateException,
* IllegalStateException, ImagingOpException, IndexOutOfBoundsException,
* MissingResourceException, NegativeArraySizeException, NoSuchElementException,
* NullPointerException, ProfileDataException, ProviderException,
* RasterFormatException, SecurityException, SystemException,
* UndeclaredThrowableException, UnmodifiableSetException,
* UnsupportedOperationException
*
* java.lang.Exception : exceptions that are checked for by the java compiler
*
* AclNotFoundException, ActivationException, AlreadyBoundException,
* ApplicationException, AWTException, BackingStoreException,
* BadAttributeValueExpException, BadBinaryOpValueExpException,
* BadLocationException, BadStringOperationException,
* BrokenBarrierException, CertificateException, ClassNotFoundException,
* CloneNotSupportedException, DataFormatException,
* DatatypeConfigurationException, DestroyFailedException,
* ExecutionException, ExpandVetoException, FontFormatException,
* GeneralSecurityException, GSSException, IllegalAccessException,
* IllegalClassFormatException, InstantiationException,
* InterruptedException, IntrospectionException,
* InvalidApplicationException, InvalidMidiDataException,
* InvalidPreferencesFormatException, InvalidTargetObjectTypeException,
* InvocationTargetException, IOException, JAXBException, JMException,
* KeySelectorException, LastOwnerException, LineUnavailableException,
* MarshalException, MidiUnavailableException, MimeTypeParseException,
* MimeTypeParseException, NamingException, NoninvertibleTransformException,
* NoSuchFieldException, NoSuchMethodException, NotBoundException,
* NotOwnerException, ParseException, ParserConfigurationException,
* PrinterException, PrintException, PrivilegedActionException,
* PropertyVetoException, RefreshFailedException, RemarshalException,
* RuntimeException, SAXException, ScriptException, ServerNotActiveException,
* SOAPException, SQLException, TimeoutException, TooManyListenersException,
* TransformerException, TransformException, UnmodifiableClassException,
* UnsupportedAudioFileException, UnsupportedCallbackException,
* UnsupportedFlavorException, UnsupportedLookAndFeelException,
* URIReferenceException, URISyntaxException, UserException, XAException,
* XMLParseException, XMLSignatureException, XMLStreamException, XPathException
*/
/* Common Exceptions
* ArithmeticException: An arithmetic operation occurs with no answer
* (Division by Zero)
*
* ClassNotFoundException: A class is called for that doesn't exist
*
* IllegalArgumentException: A method has been passed an illegal argument
*
* IndexOutOfBoundsException: Thrown when an index for an array, string is
* called for, but doesn't exist
*
* InputMismatchException: (Part of NoSuchElementException) User enters the
* wrong data type into a Scanner method
*
* IOException: An I/O operation failed
*/
import java.util.Scanner; // Library that allows us to capture user input
import java.util.*; // Allows me to check for InputMismatchException
import java.io.*; // Allows for system input and output through data streams, serialization and the file system
public class LessonSix {
// Creates a Scanner object that monitors keyboard input
static Scanner userInput = new Scanner(System.in);
public static void main(String[] args){
divideByZero(2);
System.out.print("How old are you? ");
int age = checkValidAge();
if (age != 0){
System.out.println("You are " + age + " years old");
}
getAFile("./somestuff.txt");
}
public static void divideByZero(int a)
{
try
{
// The following throws an error because you can't divide by zero
// Exception in thread "main" java.lang.ArithmeticException
System.out.println(a/0);
}
// If the exception ArithmeticException is thrown the following execute
catch (ArithmeticException e)
{
// Your custom error message
System.out.println("You can't divide by zero");
// Java's error message for this exception
System.out.println(e.getMessage());
// Prints the exception name and error message
System.out.println(e.toString());
// Prints the standard error stack trace
e.printStackTrace();
}
}
public static int checkValidAge()
{
try
{
return userInput.nextInt(); // nextInt() receives the user input
}
catch (InputMismatchException e)
{
userInput.next(); // Skips the last user input and waits for the next
System.out.print("That isn't a whole number");
return 0;
}
}
/* If you prefer to throw an exception to the calling method you use throw
* public static void getAFile(String fileName) throws IOException, FileNotFoundException
* {
* FileInputStream file = new FileInputStream(fileName);
* }
*
* If main called this method, main would have to handle the exception
*
* public static void main(String[] args) {
* try {
* getAFile("./somestuff.txt");
* }
* catch(IOException e) {
* System.out.println("An unknown IO Error Occured");
* }
*/
public static void getAFile(String fileName)
{
try
{
/* If I tried to do this without providing for an exception
* I'd get the error Unhandled Exception Type FileNotFoundException
* A checked exception is an exception the compiler forces you to protect against
*/
FileInputStream file = new FileInputStream(fileName);
}
catch (FileNotFoundException e)
{
System.out.println("Sorry I couldn't find that file");
}
// You can catch numerous exceptions (List most specific first
catch (IOException e) // Catches any IO Exception
{
System.out.println("An unknown IO Error Occured");
}
/* To ignore an exception do this
* catch (ClassNotFoundException e)
* {}
*/
/* Java 7 allows you to catch multiple exceptions at once
* catch (FileNotFoundException | IOException e)
* {}
*/
// This will catch any exception (This should always be last)
catch (Exception e)
{
System.out.println("I catch every exception");
}
// If used finally is always executed whether there was an exception or not
// It is used for clean up work like closing files and database connections
finally
{
System.out.println("");
}
}
}
Awesome and educative videos!! Thanks a lot!
Please upload the remaining videos soon.
Looking forward to be good at Java. Thanks to You!
Awesome and educative videos!! Thanks a lot!
Please upload the remaining videos soon.
Looking forward to be good at Java. Thanks to You!
Thank you. Many more are coming
difference b/w throw and throws
throws is used to designate that a method can throw an exception. throw is used to throw an exception. Does that make sense?
I like the way you explain the try and catch. Good Job, now I have a better understanding and I can practice it now.
Thank you 🙂 I’m glad the video helped you out and thank you for taking the time to show your appreciation! That means alot 😀
You are the best! Thank you for this great series! 🙂
Thank you 🙂 The whole series so far with 60 videos is available on 1 page now here Java Video Tutorial.
Many more Java tutorials are one the way. Thank you for watching
Thank you for making these videos…It helps a lot…God Bless you.
You’re very welcome 🙂 May God bless you as well
Why would you want to throws the exception up to the main instead of handling it where it happened in the method? What benefit is there in forcing it to be dealt with up in the main? I am just very confused about this and my professor’s explanation is very confusing.
Thank you, great job with the videos.
I was just showing multiple ways to handle exceptions. I try to show most everything imaginable in these tutorials. Sorry about any confusion
Hey nice tutorials. Do you have an Eclipse debugging tutorial video?
No i haven’t covered that yet
good lesson thanks very much.
You’re very welcome 🙂
I am a masters student in France and a beginner in programming.Just found ur series & have to admit that u r an excellent programmer and perfect mentor. Well done and thanks a bunch for sharing ur knowlege for free.
Thank you for the nice compliment 🙂 I’m glad you enjoy the videos.