A little confused..

oh!! Thx for your answer! Really helped!

BTW about the second one, it stores the instance of the class "IllegalArgumentException" thrown in the class PezDispenser in a variable called "iae". And we didn't name that instance and just stored it in a variable called "iae"?

Yes, "throw new IllegalArgumentException" create a new instance of the IllegalArgumentException and immediately passes it back to the method that called the method the exception was thrown in, Java will then look for a catch block that accepts objects of type IllegalArgumentException, once it finds one it passes it to the code block.

So a catch block like this: catch(IllegalArgumentException iae) is essentially saying, run me if the exception is of type IllegalArgumentException, and set it to a variable called iae inside of the catch block.

Do note that i'm simplifying things somewhat in this explanation, I'm intentionally avoiding getting too much into class inheritance for example, which plays a somewhat important role in understanding exception management, in order to keep it less confusing.

But hopefully this explanation makes you feel somewhat comfortable using and handling exceptions in your own code.

Oh, 1) But I didn't fully understand this part and immediately passes it back to the method that called the method the exception was thrown in

2) What if there are more than 1 catch blocks that accept objects of type IllegalArgumentException?

3)Why do we use try, catch blocks? Can't we just throw the exception? It shows the warning too right?

Sry for asking too many question tho..:D

1. Think of it like a reverse method call, when you call a method that takes an argument you pass an object to the method, a throw basically does the opposite, it takes an exception object and hands it back to the method that called it, and then hands it to the catch block setup to catch it.

2. Java will not compile if you have a catch clause that catches an error that will be caught by an earlier catch clause.

3. Not catching the exception leads to the program crashing, when you catch an exception you can write some code to handle that error and then resume execution of the program.

about the 2nd, can't there be 2 methods and both of them has a IllegalArgumentException? What will we do in that case if we can only write 1 exception of this type?

You can only have 1 catch block for each exception type per try block, if you have two methods you want to test for a certain exception and want different code to run based on which method failed then you'll simply have to place them in separate try...catch blocks like this:

 try {
  method1();
 } catch (IllegalArgumentException iae) {
  // deal with error;
 }

 try {
  method2();
 } catch (IllegalArgumentException iae) {
  // deal with error different way;
 }

That would be valid, when I said you could not have two catch blocks for the same exception I meant a setup like this:

 try {
  method1();
  method2();
 } catch (IllegalArgumentException iae) {
  // deal with error;
 } catch (IllegalArgumentException iae) {
  // deal with error different way;
 }

The above example would not compile, and even if it did the second catch block would never run since the IllegalArgumentException would always be caught by the first catch block.

I realize I never explicitly mentioned the fact that you can have multiple catch blocks underneath a try block, but that is indeed possible, and is what I meant to refer to in my previous comment, it should also be noted that once a method throws an exception inside of a try block none of the remaining code in the try block is executed, so you'll never have more than one exception being thrown from a try block.

Does that mean you have to explicitly throw and specify the exception before you catch it first? like throw first and then use it in the catch block?