Extend PHP's built-in exception handling class

Users can extend PHP’s built-in exception handling classes with custom exception handling classes. The following code illustrates which properties and methods in the built-in exception handling class are accessible and inheritable in subclasses. Translator's Note: The following code is only to illustrate the structure of the built-in exception handling class. It is not a usable code with practical significance.

Example #1 Built-in exception handling class

<?php
    class Exception
    { 
        protected $message = &#39;Unknown exception&#39;; // 异常信息
        protected $code = 0; // 用户自定义异常代码
        protected $file; // 发生异常的文件名
        protected $line; // 发生异常的代码行号
        function __construct($message = null, $code = 0);
        final function getMessage(); // 返回异常信息
        final function getCode(); // 返回异常代码
        final function getFile(); // 返回发生异常的文件名
        final function getLine(); // 返回发生异常的代码行号
        final function getTrace(); // backtrace() 数组
        final function getTraceAsString(); // 已格成化成字符串的 getTrace() 信息
        /* 可重载的方法 */
        function __toString(); // 可输出的字符串
}
?>

If you use a custom class to extend the built-in exception handling class and redefine the constructor, it is recommended to call parent::__construct() at the same time to check whether all variables have been is assigned a value. When the object wants to output a string, you can overload __toString() and customize the output style.

Example #2 Extending PHP’s built-in exception handling class

<?php
    /**
     * 自定义一个异常处理类
     */
    class MyException extends Exception
    {
        // 重定义构造器使 message 变为必须被指定的属性
        public function __construct($message, $code = 0) {
            // 自定义的代码
            // 确保所有变量都被正确赋值
            parent::__construct($message, $code);
        }
        // 自定义字符串输出的样式
        public function __toString() {
            return __CLASS__ . ": [{$this->code}]: {$this->message}\n";
        }
        public function customFunction() {
            echo "A Custom function for this type of exception\n";
        }
    }
    /**
     * 创建一个用于测试异常处理机制的类
     */
    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:
                    // 抛出自定义异常
                    throw new MyException(&#39;1 is an invalid parameter&#39;, 5);
                    break;
                case self::THROW_DEFAULT:
                    // 抛出默认的异常
                    throw new Exception(&#39;2 isnt allowed as a parameter&#39;, 6);
                    break;
                default:
                    // 没有异常的情况下，创建一个对象
                    $this->var = $avalue;
                    break;
            }
        }
    }
    // 例子 1
    try {
        $o = new TestException(TestException::THROW_CUSTOM);
    } catch (MyException $e) { // 捕获异常
        echo "Caught my exception\n", $e;
        $e->customFunction();
    } catch (Exception $e) { // 被忽略
        echo "Caught Default Exception\n", $e;
    }
    // 执行后续代码
    var_dump($o);
    echo "\n\n";
    // 例子 2
    try {
        $o = new TestException(TestException::THROW_DEFAULT);
    } catch (MyException $e) { // 不能匹配异常的种类，被忽略
        echo "Caught my exception\n", $e;
        $e->customFunction();
    } catch (Exception $e) { // 捕获异常
        echo "Caught Default Exception\n", $e;
    }
    // 执行后续代码
    var_dump($o);
    echo "\n\n";
    // 例子 3
    try {
        $o = new TestException(TestException::THROW_CUSTOM);
    } catch (Exception $e) { // 捕获异常
        echo "Default Exception caught\n", $e;
    }
    // 执行后续代码
    var_dump($o);
    echo "\n\n";
    // 例子 4
    try {
        $o = new TestException();
    } catch (Exception $e) { // 没有异常，被忽略
        echo "Default Exception caught\n", $e;
    }
    // 执行后续代码
    var_dump($o);
    echo "\n\n";
?>