为什么我收到“无法重新声明课程”错误？

Question

我在端口 81 上运行 Apache。我的项目文件夹是 MyPhpProject。在其中我有 2 个文件夹：域和测试。

在 Domain 文件夹中，我有 3 个 PHP 文件：

1. BaseDomain.php 包含一个抽象类 BaseDomain
   
2. Lo​​cation.php 包含一个从 BaseDomain 继承的具体类 Location
   
3. Employee.php 包含一个从 BaseDomain 继承的具体类 Employee
   

Employee类有一个Location类的引用。

这是 BaseDomain.php：

<?php
abstract class BaseDomain {

}
?>

这是 Location.php：

<?php
$returnRequire = require 'BaseDomain.php';

class Location extends BaseDomain {

    private $locationIdInt;         
    private $codeNameString;        
    private $descString;        

    public function setLocationId($locationId) {
        $this->locationIdInt = $locationId;
    }
    public function getLocationId() {
        return $this->locationIdInt;
    }

    public function setCodeName($codeName) {
        $this->codeNameString = $codeName;
    }
    public function getCodeName() {
        return $this->codeNameString;
    }

    public function setDesc($desc) {
        $this->descString = $desc;
    }
    public function getDesc() {
        return $this->descString;
    }
}
?>

这是Employee.php：

<?php
$returnRequire = require 'BaseDomain.php';

class Employee extends BaseDomain {

    private $employeeIdString;          
    private $locationObject;            

    public function setEmployeeId($employeeId) {
        $this->employeeIdString = $employeeId;
    }
    public function getEmployeeId() {
        return $this->employeeIdString;
    }

    public function setLocation($location) {
        $this->locationObject = $location;
    }
    public function getLocation() {
        return $this->locationObject;
    }
}
?>

现在在 Testing 文件夹中，我创建了一个 Test_Employee.php，这是它的代码：

<?php
set_include_path('../Domain');

$getIncludePath = get_include_path();
echo "getIncludePath = " . $getIncludePath;
echo "<br>";

$returnRequire1 = require 'Location.php';
echo "returnRequire for Location.php = " . $returnRequire1;
echo "<br>";

$returnRequire2 = require 'Employee.php';
echo "returnRequire for Employee.php = " . $returnRequire2;
echo "<br>";
?>

当我尝试运行它http://localhost:81/MyPhpProject/Testing/Test_Employee.php 时，我收到一个关于无法重新声明 BaseDomain 类的致命错误。这是我在浏览器中看到的：

getIncludePath = ../域

returnRequire for Location.php = 1

致命错误：无法在 C:\Program Files 中重新声明类 BaseDomain (x86)\Apache 软件 Foundation\Apache2.2\htdocs\MyPhpProject\Domain\BaseDomain.php 上线 2

我没有多次创建 BaseDomain 类。所以这个错误很奇怪。有人可以解释为什么我收到错误消息吗？以及如何解决它。

感谢您的宝贵时间。

Answer 1

$returnRequire1 = require 'Location.php'; 行加载 Location.php，而后者又在$returnRequire = require 'BaseDomain.php'; 行中加载 BaseDomain.php。然后，$returnRequire2 = require 'Employee.php'; 行加载 Employee.php，它（再次）加载 BaseDomain.php（$returnRequire = require 'BaseDomain.php'; 行）。 BaseDomain.php 的第二次加载导致 php 尝试重新定义 BaseDomain 类，这是不允许的。

解决此问题的最简单方法是将您的require 调用更改为require_once。这将确保每个文件在每次运行时只加载一次，从而避免您遇到的错误。

Answer 2

BaseDomain.php：

<?php
abstract class BaseDomain {

}
?>

位置.php

<?php
class Location extends BaseDomain {

    private $locationIdInt;         
    private $codeNameString;        
    private $descString;        

    public function setLocationId($locationId) {
        $this->locationIdInt = $locationId;
    }
    public function getLocationId() {
        return $this->locationIdInt;
    }

    public function setCodeName($codeName) {
        $this->codeNameString = $codeName;
    }
    public function getCodeName() {
        return $this->codeNameString;
    }

    public function setDesc($desc) {
        $this->descString = $desc;
    }
    public function getDesc() {
        return $this->descString;
    }
}
?>

Employee.php：

<?php

class Employee extends BaseDomain {

    private $employeeIdString;          
    private $locationObject;            

    public function setEmployeeId($employeeId) {
        $this->employeeIdString = $employeeId;
    }
    public function getEmployeeId() {
        return $this->employeeIdString;
    }

    public function setLocation($location) {
        $this->locationObject = $location;
    }
    public function getLocation() {
        return $this->locationObject;
    }
}
?>

Test_Employee.php

<?php
set_include_path(__DIR__.'/MyPhpProject/Domain');
require 'BaseDomain.php';

$getIncludePath = get_include_path();
echo "getIncludePath = " . $getIncludePath;
echo "<br>";

$returnRequire1 = require 'Location.php';
echo "returnRequire for Location.php = " . $returnRequire1;
echo "<br>";

$returnRequire2 = require 'Employee.php';
echo "returnRequire for Employee.php = " . $returnRequire2;
echo "<br>";
?>