認識 PHP 物件導向（一）

OOP
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前言

本文為〈PHP OO 基礎教學〉一文的學習筆記。

類別與物件

類別（Class）：可以比喻為一間房子的藍圖，定義房子的結構與形狀。

物件（Object）：可以比喻為一棟真的房子，是類別的實例化。

建立類別

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class MyClass
{
    //
}

$obj = new MyClass;

var_dump($obj);

結果：

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object(MyClass)#1 (0) {
}

定義類別屬性

屬性（Property）：也稱作類別的變數。

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class MyClass
{
    public $prop = "I'm a class property!";
}

$obj = new MyClass;

var_dump($obj);

結果：

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object(MyClass)#1 (1) {
    ["prop"]=>
    string(21) "I'm a class property!"
}

使用箭頭「->」來存取物件的屬性和方法。

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class MyClass
{
    public $prop = "I'm a class property!";
}

$obj = new MyClass;

echo $obj->prop;

結果：

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I'm a class property!

定義類別方法

方法（Method）：類別裡面的函式。

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class MyClass
{
    public $prop = "I'm a class property!";

    public function setProperty($new)
    {
        $this->prop = $new;
    }

    public function getProperty()
    {
        return $this->prop . "<br />";
    }
}

$obj = new MyClass;

echo $obj->getProperty();

$obj->setProperty("I'm a new class property!");

echo $obj->getProperty();
  • $this 就如同直接使用物件名稱來指定物件。

結果：

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I'm a class property!
I'm a new class property!

實例化第二個類別：

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$obj2 = new MyClass;

echo $obj2->getProperty();

$obj2->setProperty("I belong to the second instance!");

echo $obj2->getProperty();

結果：

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I'm a class property!
I'm a new class property!
I'm a class property!
I belong to the second instance!

魔術函數

  1. __construct() 建構子，類別一旦宣告後就直接執行，用來執行必要動作如：資料庫連線等。
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class MyClass
{
    public $prop = "I'm a class property!";

    public function __construct()
    {
        echo 'The class "', __CLASS__, '" was initiated!<br />';
    }

    public function setProperty($new)
    {
        $this->prop = $new;
    }

    public function getProperty()
    {
        return $this->prop . "<br />";
    }
}

$obj = new MyClass;

echo $obj->getProperty();

$obj->setProperty("I'm a new class property!");

echo $obj->getProperty();
  • __CLASS__ 魔術常數（Magic constant），會回傳被呼叫的類別的名稱。

結果：

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The class "MyClass" was initiated!
I'm a class property!
I'm a new class property!
  1. __destruct() 解構子，用來執行收尾動作如：關閉資料庫連線等。
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class MyClass
{
    public $prop = "I'm a class property!";

    public function __construct()
    {
        echo 'The class "', __CLASS__, '" was initiated!<br />';
    }

    public function __destruct()
    {
        echo 'The class "', __CLASS__, '" was destroyed!<br />';
    }

    public function setProperty($new)
    {
        $this->prop = $new;
    }

    public function getProperty()
    {
        return $this->prop . "<br />";
    }
}

$obj = new MyClass;

echo $obj->getProperty();

$obj->setProperty("I'm a new class property!");

echo $obj->getProperty();

結果：

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The class "MyClass" was initiated!
I'm a class property!
I'm a new class property!
The class "MyClass" was destroyed!
  1. __toString()，當物件被當作字串處理時觸發，可以將物件轉換為字串。
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class MyClass
{
    public $prop = "I'm a class property!";

    public function __construct()
    {
        echo 'The class "', __CLASS__, '" was initiated!<br />';
    }

    public function __destruct()
    {
        echo 'The class "', __CLASS__, '" was destroyed.<br />';
    }

    public function __toString()
    {
        echo "Using the toString method.<br />";
        return $this->getProperty();
    }

    public function setProperty($new)
    {
        $this->prop = $new;
    }

    public function getProperty()
    {
        return $this->prop . "<br />";
    }
}

$obj = new MyClass;

echo $obj;

結果：

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The class "MyClass" was initiated!
Using the toString method.
I'm a class property!
The class "MyClass" was destroyed.

摧毀物件

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unset($obj);