Java Reference
In-Depth Information
If getParameter() returns, say, the non-numeric string “abc , then the
Integer.parseInt() method cannot possibly parse the string into a numeric
value. Obviously this would cause a serious problem. Java exception handling
provides a systematic way for the programmer to respond to such errors and to
decide on an appropriate response rather than simply letting the program fail,
perhaps ungracefully. Without an exception-handling system built into the lan-
guage, you would have to write your own routine to test the string for numeric
numbers. For example, in the code below we create a special method to test if
a String holds a valid integer value before the string goes to the parseInt
method:
...
String str = getParameter ( " dat " );
if (testIfInt (str))
Integer.parseInt (str);
else {
ErrorFlag = MY - ERROR - BAD - FORMAT;
return 1;
}
boolean testIfInt (String str) {
...messy code to test characters for numbers. .
}
...
Thankfully, we can instead use Java exception handling rather than having to
write custom test code for all possibilities, or worse, letting a program fail
ungracefully. In Java exception handling, an exception is said to be “thrown”
when the JVM detects that something is awry. In the example here, the attempt
to parse a non-numeric string throws a particular type of exception called a
NumberFormatException .
Whenever an exception is possible, our code can “catch” the exception, should
one occur, using the try-catch syntax as follows:
try {
code that can throw an exception
}
catch (Exception e) {
code to handle the exception
}
In the following code segment we surround the parseInt() method invocation
 
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