NullPointerException*
You tried to access an object (either a field
in an object or a method of an object). This
did not work because the object reference you
used to access the object was 'null'. For
example: You wrote "thing.print()", and "thing"
was null at the time.

ArithmeticException*
Something went wrong during an arithmetic
calculation, such as a division by 0 or
something similar.

StringIndexOutOfBoundsException*
You have tried to access a character or a substring
in a string , and the index you used does not exist
in that string. For example, you may have tried to
access the fifth character in a string that is only
three characters long.
For the substring operation, remember that the second
parameter is the end index of the substring, not the
lentgh.

ClassCastException*
You used a "cast" - that is an instruction assigning
a different static type to an object, such as in this
example:
       (String)someObject
Here, "someObject" is cast to "String". This is legal
only if the object stored in someObject really is of
type String.
In other words: you can cast to type T only if the
object you are casting is of type T or one of its
subtypes. In your case it wasn't.

IndexOutOfBoundsException*
An index of some sort (such as to an array, to a string,
or to a vector) is out of range. "Out of range" means
that the index does not exist in the array or other
collection (e.g. you tried to access element 5, but only
three elements exist).

ArrayIndexOutOfBoundsException*
An array index is out of range. "Out of range" means
that the index does not exist in the array (e.g. you
tried to access element 5, but only three elements
exist). The legal index range is 0..arraylength-1.

ConcurrentModificationException*
You are doing an iteration over a collection here.
While you are doing this, the collection was modified.
That's a problem. You are not allowed to modify the
collection during an iteration. Or the other way
around: you cannot continue the iteration after
modifying the collection. The only modification
allowed during an iteration is removing elements with
the Iterator's remove method (NOT the remove in the
collection itself).

AssertionError*
An assertion has failed. This means that the expression
inside the assert statement
    assert(assertion-expression)
evaluated to false. The assertion was put there most
likely to ensure that the assertion is true at this
point, and it being false indicates some sort of error.
The exact nature of this error depends on the program.
You should investigate why this expression was false.

ClassNotFoundException*
A class that was needed to execute this application
could not be found. It seems that it was found at the
time the application was compiled, but now it's gone.
Possible causes could be that your Java system is not
configured properly (if the class in question is a 
system class) or that your project is damaged (some
class files somehow got lost or corrupted).
Try rebuilding your whole project. If the problem 
persists, chack with other projects. If this happens
with more than one project, you may need to reinstall
JDK.

ArrayStoreException*
No help available - sorry.

CannotRedoException*
No help available - sorry.

CannotUndoException*
No help available - sorry.

CMMException*
No help available - sorry.

EmptyStackException*
No help available - sorry.

IllegalArgumentException*
No help available - sorry.

IllegalMonitorStateException*
No help available - sorry.

IllegalPathStateException*
No help available - sorry.

IllegalStateException*
No help available - sorry.

ImagingOpException*
No help available - sorry.

MissingResourceException*
No help available - sorry.

NegativeArraySizeException*
No help available - sorry.

NoSuchElementException*
No help available - sorry.

ProfileDataException*
No help available - sorry.

ProviderException*
No help available - sorry.

RasterFormatException*
No help available - sorry.

SecurityException*
No help available - sorry.

SystemException*
No help available - sorry.

UndeclaredThrowableException*
No help available - sorry.

UnsupportedOperationException*
No help available - sorry.

Exception
This is a general exception that only says
that something went wrong. I have no idea
what it is...