Classes and objects in Java - JavaTech: An Introduction to Scientific and Technical Computing with Java - page 82

with a try-catch pair:
try {
int data = Integer.parseInt (getParameter ("dat"));
aFunctionSetup (data);
...
}
catch (NumberFormatException e) {
data = -1;
}
Here, the Integer class method parseInt() throws an instance of the
NumberFormatException class if the string passed does not represent a valid
integer number. The program processing jumps from the line that causes the
exception (the parseInt() method call) to the code in the catch block. All
the code from the line that caused the exception to the end of the try block is
permanently skipped.
The parseInt() method in Integer is written something like the
following:
public static int parseInt (String s)
throws NumberFormatException {
...
... code to check if the string is a number
... if it isn't then :
throw new NumberFormatException ("some error message");
...
}
The throws NumberFormatException phrase in the method signature indi-
cates that the method includes a throw statement of that type somewhere in the
method code.
We see that the throw statement actually creates an instance of the exception
(like everything else in Java, exceptions are class types) and causes the routine to
return with the exception thrown. The constructors for an exception may include
parameters with which you can pass useful information about the circumstances
of the exception. The catch code can then examine this information using methods
on the Exception class.
Java divides exceptions into two categories:
general exceptions
run-time exceptions
General exceptions must be handled in source code. They are also called
“checked” exceptions, meaning they must be checked for. For any method that