throw an exception in code

[Dlangdaman]

i personally am having a hard time grasping the exceptions thing and honestly the JAVA language as a whole. I am finding it very rough to focus on and am slowly falling behind in my class. do you know of any good tutorials or books that may help me graspe it faster or easier? i have another assignment due this week and I have no clue (unfortunately) on how to even start

[r035198x]

i personally am having a hard time grasping the exceptions thing and honestly the JAVA language as a whole. I am finding it very rough to focus on and am slowly falling behind in my class. do you know of any good tutorials or books that may help me graspe it faster or easier? i have another assignment due this week and I have no clue (unfortunately) on how to even start

You'll have to be willing to put in a few extra hours on it. After going through this thread you really should have grasped exceptions. So many code examples have been posted on how to use a try / catch block. You see, if you actually read those responses carefully you will grasp the thing.

[blazedaces]

i personally am having a hard time grasping the exceptions thing and honestly the JAVA language as a whole. I am finding it very rough to focus on and am slowly falling behind in my class. do you know of any good tutorials or books that may help me graspe it faster or easier? i have another assignment due this week and I have no clue (unfortunately) on how to even start

Listen, despite what you may think about our "snide remarks" we really want to help. We really want you to understand and grasp this idea and to do well in your class. That's why we offered our input and help. So I ask you, what specifically do you not understand?

You may not know the answer so let me try and break it down into a few topics at least. Help us to help you. ;)

-What is an exception?

-What is happening in the exception "class" you were suggested to create for yourself? (i.e. what does super(s) mean? If you've never done java, you may not know.)

-What does "throw new MyException(Str ing message)" actually do?

I honestly think you're tackling too much at a time right now from the way you sound. Perhaps you're trying to tackle a problem that takes too much previous knowledge. Take it slow. Find out what every single thing means, it's a lot to take in, but with a good amount of hard work I'm sure you can do it.

I'll continue with some more questions, there are more...

-What is does putting part of my code in try brackets do? What does putting part of my code in catch brackets do?

-How does this all relate? Why throw an exception? Why catch it?

I'll try to explain a few things here, hopefully it'll help. Most of this is repeated summarization:

In part of your code you want to throw an exception when the grade is above 100 or below 0 right? So somewhere you throw the exception like this:

throw new MyException("message")

To do this you need a class called MyException that would look like this:

class MyException extends Exception //extending means you basically inherit the methods of that class. Exception is the master class of all exceptions and all other exceptions must extend the Exception class or a class that already extends it...
{
    public MyException(String s) {
        super(s);  //super(s) means that in this circumstance you do to the string whatever your "extended" class would do to it.  In this case super(s) for the exception class simply saves the message.  So when you throw new MyException("an exception occured") that will be sent with the exception, wherever it is caught (catch...?)
    }
}

That's all that throwing an exception does. It simply sends a message and yells to the computer "AN EXCEPTION!!!111 !1one!!".

Somewhere else, wherever you run this method, you have to catch the exception. What does that mean? Well, like we said earlier, a thrown exception just tells the computer that an exception was thrown. Wherever you catch it, that's where you tell the computer what to do if you catch an exception. Anything making better sense?

Also, I suggest keeping it simple. Don't add a dialog pop up. Just use the scanner class and ask the user a question and request an input. Have you learned to do that yet?

Anyways, good luck again, and don't give up!

-blazed

[Dlangdaman]

I have not yet learned that

[JosAH]

I have not yet learned that

Well, your options are simple then: either don't use Exceptions at all (I don't
recommend that option) or start reading up on what Exceptions are all about.
It's not that difficult; you'll get the hang of it.

Basically you throw an Exception when normal control flow can't continue and
you don't know what to do anymore to 'repair' the situation. It's up to the caller
of your method to 'handle' that Exception, i.e. your method throws an Exception,
a caller catches it and handles it; if it can't handle it, is shouldn't catch it and
leave the handling to its own caller, etc. etc. that's all there is to it.

kind regards,

Jos

[tnga]

Dlangdaman,

Is that a requirement in your execise lab to use exceptions?
If not, I suggest you wait for your teacher to teach exceptions in class...

Regards,

TNGA

[Dlangdaman]

it unfortunately is needed..we have touched them, what I meant we havent learned is how to use the scanner class

[blazedaces]

it unfortunately is needed..we have touched them, what I meant we havent learned is how to use the scanner class

Wow dude... I'm surprised. Just so you know though, learning to use the scanner class is A Lot easier then learning to throw/catch/use exceptions...

The scanner class is just an easy way to read inputs.

For example:

[code=java]
import java.util.*; //The scanner class is inside java.util.Scann er

public class ScannerExample {

public static void main(String args[]) {
Scanner scannerVariable Name = new Scanner(System. in); //The way to declare scanner
System.out.prin tln("Please input a string: "); //Asks the user to input a string
String inputtedString = scannerVariable Name.next(); //Accepts a string input
System.out.prin tln();
System.out.prin tln("The following is the inputted string tokenized by whitespace: " + inputtedString) ;
//Now if you wanted to input an int you could do this:

System.out.prin tln("Please input an int: "); //Asks the user to input an int
int inputtedint = scannerVariable Name.nextInt(); //Accepts an int input
System.out.prin tln();
System.out.prin tln("The following is the inputted int: " + inputtedint);
}
}
[/code]

The output after you compile would look like this:

--------------------Configuration: <Default>--------------------
Please input a string: 
examplestring

The following is the inputted string tokenized by whitespace: examplestring
Please input an int: 
10

The following is the inputted int: 10

Process completed.

There's also readLine(), which reads a whole line (technically it's just tokenized by '\n', and readDouble() and all that jazz...

Now the scanner class can do a lot more then that, to find out more, check out it's documentation: http://java.sun.com/j2se/1.5.0/docs/...l/Scanner.html

Good luck man,

-blazed