在PHP中 $this->,self::,static:: 都可以用来调用变量或方法，其中 $this 指向当前对象，用于访问非静态变量和非静态方法（静态变量和方法认为是类的元素）；
self和static都是用于访问静态变量和方法，他们区别在于，self 是访问self所在类，而static也叫延迟绑定，访问的是被当前子类的静态变量和方法，请看以下例程：

abstract class A
{
    protected $strA = 'this is $strA in class A ';
    protected static $strB =  'this is static $strB in class A';

    public  function show_info()
    {
        echo "called class::";echo get_called_class();echo PHP_EOL;
        echo $this->strA;echo PHP_EOL;
        echo self::$strB;echo PHP_EOL;
        echo static::$strB;echo PHP_EOL;


    }
}

class B extends A
{
    protected static $strB =  'this is static $strB in class B';

    public function show_info()
    {
        parent::show_info();
    }


}

$objB = new B();
$objB->show_info();

输出：

called class::B
this is $strA in class A
this is static $strB in class A
this is static $strB in class B