php面向对象类中的$this，static，final，const，self这几个关键字使用方法。

<?php
<span style="color:#ff0000;">// this是指向当前对象的指针</span>
class test_this{
    private $content; //定义变量
    function __construct($content){ //定义构造函数
          $this->content= $content;
    }
    function __destruct(){}//定义析构函数
    function printContent(){//定义打印函数
        echo $this->content.'<br />';
    }
}
$test=new test_this('北京欢迎你！'); //实例化对象
$test->printContent();//北京欢迎你！
$test=new test_this('新年新气象！');//再一次实例化对象
$test->printContent();//新年新气象！
echo '<br />';
<span style="color:#ff0000;">//self是指向类的本身，只跟类有关，跟任何对象实例无关</span>
class test_self{
    private static $first_count; //定义静态变量
    private $last_count;
    function __construct(){
        $this->last_count=++self::$first_count;//直接用self调用变量的值赋值给另一个变量
    }
    function __destruct(){}
    function print_self(){
        print($this->last_count);
    }
}
$abc=new test_self();//实例化对象
$abc->print_self();//1
echo '<br />';
<span style="color:#ff0000;">//parent是指向父类的指针</span>
class test_parent{ //基类
    public $name;  //定义姓名  父类成员需要定义为public，才能够在继承类中直接使用 this来调用。
    function __construct($name){
        $this->name=$name;
    }
}
class test_son extends test_parent{ //派生类  继承test_parent
    public $gender;//定义性别
    public $age;    //定义年龄
    function __construct($gender,$age){ //继承类的构造函数
        parent::__construct('nostop');//使用parent调用父类的构造函数,来进行对父类的实例化
        $this->gender=$gender;
        $this->age=$age;
    }
    function __destruct(){}
    function print_info(){
        echo $this->name.'是个'.$this->gender.'，今年'.$this->age.'岁'.'<br />';
    }
}
$nostop=new test_son('女性','22');//实例化test_son对象
$nostop->print_info();//执行输出函数  nostop是个女性，今年23岁
?>

$this

<span style="font-size:14px;"><?php
class MyClass{
	private $name;
	public  function __construct($name){
		$this->name=$name;
	}
	public function getname(){
		return $this->name;
	}
	public  function printName(){
		echo $this->getname();
	}
}
$myclass= new MyClass("I Like PHP");
$myclass->printName();//输出：I Like PHP
?></span>

static

<?php
class MyObject{
	public static $myStaticVar=0;
	function myMethod(){
		self::$myStaticVar+=2;
		echo self::$myStaticVar;
	}
}
$instance1=new MyObject();
$instance1->myMethod();
$instance2=new MyObject();
$instance2->myMethod();
//结果将分别打印2、4

<?php
class Book{
	static $num=0;
	public function showMe(){
		echo"您是滴".self::$num."位访客";
		self::$num++;
	}
}
$book1=new Book();
$book1->showMe();
echo"<br>";
$book2=new Book();
$book2->showMe();
echo"<br>";
echo"您是滴".Book::$num."位访客";
?>

final

<?php
final class MyClass{//此类将不允许被继承
	final function fun1(){......}//此方法将不允许被重写
}

const

<?php
class clss_a{
	private static $name="static class_a"; 
	const PI=3.14; 
	public $value; 
	public static function getName(){ 
		return self::$name; 
	} 
	//这种写法有误，静态方法不能访问非静态属性 
	public static function getName2(){ 
		return self::$value; 
	} 
	public function getPI(){ 
		return self::PI; 
	}
}

self

PHP中 :: 、-> 、self 、$this操作符的区别

<?php
class Fruit {
    const CONST_VALUE = 'Fruit Color';
}
$classname = 'Fruit';
echo $classname::CONST_VALUE; // As of PHP 5.3.0
echo Fruit::CONST_VALUE;
?>

<?php
class Fruit {
    const CONST_VALUE = 'Fruit Color';
}
class Apple extends Fruit
{
    public static $color = 'Red';
    public static function doubleColon() {
        echo parent::CONST_VALUE . "\n";
        echo self::$color . "\n";
    }
}

<?php
class Fruit
{
    protected function showColor() {
        echo "Fruit::showColor()\n";
    }
}
class Apple extends Fruit
{
    // Override parent's definition
    public function showColor()
    {
        // But still call the parent function
        parent::showColor();
        echo "Apple::showColor()\n";
    }
}
$apple = new Apple();
$apple->showColor();
?>

  
<?php
    class Apple
    {
        public function showColor()
        {
            return $this->color;
        }
    }
    class Banana
    {
        public $color;

        public function __construct()
        {
            $this->color = "Banana is yellow";
        }
        public function GetColor()
        {
            return Apple::showColor();
        }
    }
    $banana = new Banana;
    echo $banana->GetColor();
?>

    
<?php
class Fruit
{
    static function color()
    {
        return "color";
    }
    static function showColor()
    {
        echo "show " . self::color();
    }
}
class Apple extends Fruit
{
    static function color()
    {
        return "red";
    }
}
Apple::showColor();
// output is "show color"!
?>