Exception handling mechanism of PHP5 with new features_PHP tutorial

　php(as the current mainstream development language)Error handling before 5 years old
In php(as the current mainstream development language) Program error handling before 5 mostly used the following three methods:
　1. Use the trigger_error() or die() function to generate a script-level warning or fatal error;
　
　2. Return an error flag (such as false) in a class method or function, or set a property or global variable that can be checked later (such as $error), and then check its value in an appropriate place before deciding whether to continue executing the program (such as if ($error==1){});
　
　3. Use PEAR to handle errors;
　
　(1) Use die() or trigger_error()
You can use die() function to end program execution. Below is a simple class that attempts to load a class file from a directory.
　(as the current mainstream development language) ?>
　
　(as the current mainstream development language) )
　// php(as the current mainstream development language) 4
　require_once(cmd_php(as the current mainstream development language)4/Command .php(as the current mainstream development language));
　class CommandManager {
　var $cmdDir = "cmd_php(as the current mainstream development language)4 ";
　
　function getCommandObject($cmd) {
　$path = "{$this->cmdDir}/{$cmd}.php(as the current mainstream development language)";
　if (!file_exists($path)) {
　die("Cannot find $path ");
　}
Require_once $path;

if (!class_exists($cmd)) {
die("class $cmd does not exist");
}
　
　$ret = new $cmd();
　if (!is_a($ret, Command)) {
　die("$cmd is not a Command");
　}
Return $ret;
　}
　}
　?>
　
This is a way to use php(as the current mainstream development language) to implement "Command Pattern design" A simple example of "Pattern" (see "Java and Patterns"). Programmers who use this class (client coder) can put a class in the directory (in the example, cmd_php(as the current mainstream Development language) 4 directory). Once the file has the same name as the class contained in it, and this class is a subclass of the Command class, our class method will generate a usable Command object defined in the Command class. The method is used to execute the found command, that is, the object returned by the getCommandObject() method will execute execute(). Mainstream development language)
4/Command.php
(as the current mainstream development language)　　　(as the current mainstream development language). Mainstream development language)
4/Command.php
(as the current mainstream development language)?>　　(as the current mainstream development language) Language)

　// php(as the current mainstream development language) 4
　class Command {　function execute() {　die("Command:: execute() is an abstract method");
　}
　}
　?>
　
You can see that Command is php
(as the current mainstream development language) For the implementation of the abstract class in
4, we cannot instantiate it directly, but must first derive a subclass from it and then instantiate it. When we use php
(as the current mainstream development language) After 5, we can use a better way - use the abstract keyword to declare classes and methods as "abstract": 　　　
　(As the current mainstream development language)

// php(As the current mainstream development language) 5
Abstract class Command {Abstract function execute( ; This class is named realcommand and can be found in the cmd_php(as the current mainstream development language)
4/realcommand.php
(as the current mainstream development language)
file.
　
　(as the current mainstream development language)4/realcommand.php(as the current mainstream development language)?>
　
　(as the current mainstream development language)
　// php(as the current mainstream development language) 4
require_once Command.php(as the current mainstream development language);
class realcommand extends Command {
function execute() {
print "realcommand::execute() executing as ordered sah! ";
　}
　}
　?>
　
Using such a structure can make the code very flexible. You can add a new Command class at any time without changing the surroundings framework. But you have to be aware of some potential factors that abort script execution. We need to ensure that the class file exists, and that the class is a subclass of Command (just like realcommand).
In the example, if the operation we try to find the class fails, the script execution will be terminated, which reflects the safety of the code. However, this code is not flexible enough and the extreme reflection is that the class method can only be used. Performing positive operations, it is only responsible for finding and instantiating a Command object. It cannot handle errors in the wider scope of script execution (of course it should not be responsible for handling errors if we add too many to a certain class method. associated with surrounding code, then the reuse of this class will become difficult and difficult to extend)

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