PHP 面向对象编程：解决继承中遇到的 NULL 值问题与正确设计类关系

// 原始 Patient 类片段
class Patient{
    private $name;
    private $age;
    private $gender;

    public function record($name, $age, $gender){
        $this->name = $name;
        $this->age = $age;
        $this->gender = $gender;
    }
    // ...
}

// 原始 Clinic 类片段
class Clinic extends Patient{
    private $patients = [];

    public function assignPatient($name, $age, $gender){
        // 问题所在：这里调用了 new Patient()
        // 但 Patient 类中没有定义构造函数，record() 也未被调用
        $this->patients[] = new Patient($name, $age, $gender);
    }
    // ...
}

<?php
class Patient{
    private $name;
    private $age;
    private $gender;

    /**
     * 构造函数：在创建 Patient 对象时自动调用，用于初始化病人信息。
     *
     * @param string $name 病人姓名
     * @param int $age 病人年龄
     * @param string $gender 病人性别
     */
    public function __construct($name, $age, $gender){
        $this->name = $name;
        $this->age = $age;
        $this->gender = $gender;
    }

    // 获取病人姓名
    public function getName(){
        return $this->name;
    }

    // 获取病人年龄
    public function getAge(){
        return $this->age;
    }

    // 获取病人性别
    public function getGender(){
        return $this->gender;
    }
}
?>

<?php
class Clinic {
    private $patients = []; // 诊所拥有一组病人

    /**
     * 获取诊所中的所有病人列表。
     *
     * @return array 包含 Patient 对象的数组
     */
    public function getPatients(){
        return $this->patients;
    }

    /**
     * 向诊所添加一位新病人。
     *
     * @param string $name 病人姓名
     * @param int $age 病人年龄
     * @param string $gender 病人性别
     */
    public function assignPatient($name, $age, $gender){
        // 使用正确初始化的 Patient 对象添加到病人列表
        $this->patients[] = new Patient($name, $age, $gender);
    }

    /**
     * 根据索引从诊所中删除一位病人。
     *
     * @param int $index 要删除病人的索引
     */
    public function deletePatient($index){
        if (isset($this->patients[$index])) {
            unset($this->patients[$index]);
            // 重置数组索引以避免空洞，可选操作
            $this->patients = array_values($this->patients);
        }
    }
}
?>

<?php
// Patient 类定义
class Patient{
    private $name;
    private $age;
    private $gender;

    public function __construct($name, $age, $gender){
        $this->name = $name;
        $this->age = $age;
        $this->gender = $gender;
    }

    public function getName(){
        return $this->name;
    }

    public function getAge(){
        return $this->age;
    }

    public function getGender(){
        return $this->gender;
    }
}

// Clinic 类定义
class Clinic {
    private $patients = [];

    public function getPatients(){
        return $this->patients;
    }

    public function assignPatient($name, $age, $gender){
        $this->patients[] = new Patient($name, $age, $gender);
    }

    public function deletePatient($index){
        if (isset($this->patients[$index])) {
            unset($this->patients[$index]);
            // 可选：重新索引数组，使键连续
            $this->patients = array_values($this->patients);
        }
    }
}

// 实例化并操作
$clinic = new Clinic();

$clinic->assignPatient("Patrick star", 18, "Male");
$clinic->assignPatient("SpongeBob Squarepants", 17, "Male");
$clinic->assignPatient("Eugene Krab", 28, "Male");

echo "Initial patient list:\n";
print_r($clinic->getPatients());

$clinic->deletePatient(1); // 删除索引为1的病人 (SpongeBob Squarepants)

echo "\nPatient list after deletion:\n";
print_r($clinic->getPatients());

?>

Initial patient list:
Array
(
    [0] => Patient Object
        (
            [name:Patient:private] => Patrick star
            [age:Patient:private] => 18
            [gender:Patient:private] => Male
        )

    [1] => Patient Object
        (
            [name:Patient:private] => SpongeBob Squarepants
            [age:Patient:private] => 17
            [gender:Patient:private] => Male
        )

    [2] => Patient Object
        (
            [name:Patient:private] => Eugene Krab
            [age:Patient:private] => 28
            [gender:Patient:private] => Male
        )

)

Patient list after deletion:
Array
(
    [0] => Patient Object
        (
            [name:Patient:private] => Patrick star
            [age:Patient:private] => 18
            [gender:Patient:private] => Male
        )

    [1] => Patient Object
        (
            [name:Patient:private] => Eugene Krab
            [age:Patient:private] => 28
            [gender:Patient:private] => Male
        )

)