PYTHON Extending Exceptions

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PHP Extending Exceptions

PHP original manual for Extending Exceptions [ show | php.net ]

Extending Exceptions

A User defined Exception class can be defined by extending the built-in Exception class. The members and properties below, show what is accessible within the child class that derives from the built-in Exception class.

Example #1 The Built in Exception class

<?php
class Exception
{
    protected 
$message 'Unknown exception';   // exception message
    
protected $code 0;                        // user defined exception code
    
protected $file;                            // source filename of exception
    
protected $line;                            // source line of exception

    
function __construct($message null$code 0);

    final function 
getMessage();                // message of exception 
    
final function getCode();                   // code of exception
    
final function getFile();                   // source filename
    
final function getLine();                   // source line
    
final function getTrace();                  // an array of the backtrace()
    
final function getTraceAsString();          // formated string of trace

    /* Overrideable */
    
function __toString();                       // formated string for display
}
?>

If a class extends the built-in Exception class and re-defines the constructor, it is highly recomended that it also call parent::__construct() to ensure all available data has been properly assigned. The __toString() method can be overriden to provide a custom output when the object is presented as a string.

Example #2 Extending the Exception class

<?php
/**
 * Define a custom exception class
 */
class MyException extends Exception
{
    
// Redefine the exception so message isn't optional
    
public function __construct($message$code 0) {
        
// some code
    
        // make sure everything is assigned properly
        
parent::__construct($message$code);
    }

    
// custom string representation of object
    
public function __toString() {
        return 
__CLASS__ ": [{$this->code}]: {$this->message}\n";
    }

    public function 
customFunction() {
        echo 
"A Custom function for this type of exception\n";
    }
}


/**
 * Create a class to test the exception
 */
class TestException
{
    public 
$var;

    const 
THROW_NONE    0;
    const 
THROW_CUSTOM  1;
    const 
THROW_DEFAULT 2;

    function 
__construct($avalue self::THROW_NONE) {

        switch (
$avalue) {
            case 
self::THROW_CUSTOM:
                
// throw custom exception
                
throw new MyException('1 is an invalid parameter'5);
                break;

            case 
self::THROW_DEFAULT:
                
// throw default one.
                
throw new Exception('2 is not allowed as a parameter'6);
                break;

            default: 
                
// No exception, object will be created.
                
$this->var $avalue;
                break;
        }
    }
}


// Example 1
try {
    
$o = new TestException(TestException::THROW_CUSTOM);
} catch (
MyException $e) {      // Will be caught
    
echo "Caught my exception\n"$e;
    
$e->customFunction();
} catch (
Exception $e) {        // Skipped
    
echo "Caught Default Exception\n"$e;
}

// Continue execution
var_dump($o);
echo 
"\n\n";


// Example 2
try {
    
$o = new TestException(TestException::THROW_DEFAULT);
} catch (
MyException $e) {      // Doesn't match this type
    
echo "Caught my exception\n"$e;
    
$e->customFunction();
} catch (
Exception $e) {        // Will be caught
    
echo "Caught Default Exception\n"$e;
}

// Continue execution
var_dump($o);
echo 
"\n\n";


// Example 3
try {
    
$o = new TestException(TestException::THROW_CUSTOM);
} catch (
Exception $e) {        // Will be caught
    
echo "Default Exception caught\n"$e;
}

// Continue execution
var_dump($o);
echo 
"\n\n";


// Example 4
try {
    
$o = new TestException();
} catch (
Exception $e) {        // Skipped, no exception
    
echo "Default Exception caught\n"$e;
}

// Continue execution
var_dump($o);
echo 
"\n\n";
?>