php中::的使用

类中 静态方法和静态属性的引用方法

class Test{
     public static $test = 1;
    public static function test(){
    }
}

可以不用实例化对象直接使用 Test::$test 来取得$test属性的值
静态方法调用也同理Test::test(); 直接调用静态方法test

1用变量在类定义外部访问

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

2.在类定义外部使用::

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

3.调用parent方法

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

//Fruit::showColor()
//Apple::showColor()

4.使用作用域限定符

    <?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();
    ?>
//Banana is yellow

5.调用基类的方法

<?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"!
     //show color