User Guide

984 Chapter 2: ActionScript Language Reference
try..catch..finally
Availability
Flash Player 7.
Usage
try {
// ... try block ...
} finally {
// ... finally block ...
}
try {
// ... try block ...
} catch(error[:ErrorType1]) {
// ... catch block ...
} [catch(error[:ErrorTypeN]) {
// ... catch block ...
}] [finally {
// ... finally block ...
}]
Parameters
error
The expression thrown from a throw statement, typically an instance of the Error class
or one of its subclasses.
ErrorType An optional type specifier for the error identifier. The catch clause catches only
errors of the specified type.
Description
Keywords; enclose a block of code in which an error can occur, and then respond to the error. If
any code within the
try code block throws an error (using the throw statement), control passes to
the
catch block, if one exists, and then to the finally code block, if one exists. The finally
block always executes, regardless of whether an error was thrown. If code within the
try block
doesn’t throw an error (that is, if the
try block completes normally), then the code in the
finally block is still executed. The finally block executes even if the try block exits using a
return statement.
A
try block must be followed by a catch block, a finally block, or both. A single try block can
have multiple
catch blocks but only one finally block. You can nest try blocks as many levels
deep as desired.
The
error parameter specified in a catch handler must be a simple identifier such as e or
theException or x. The variable in a catch handler can also be typed. When used with multiple
catch blocks, typed errors let you catch multiple types of errors thrown from a single try block.
If the exception thrown is an object, the type will match if the thrown object is a subclass of the
specified type. If an error of a specific type is thrown, the
catch block that handles the
corresponding error is executed. If an exception that is not of the specified type is thrown, the
catch block does not execute and the exception is automatically thrown out of the try block to a
catch handler that matches it.
CHAPTER 2
ActionScript Language Reference