PHP双冒号::的用法

双冒号操作符即作用域限定操作符Scope Resolution Operator可以访问静态、const和类中重写的属性与方法。

在类定义外使用的话，使用类名调用。在PHP 5.3.0，可以使用变量代替类名。

Program List：用变量在类定义外部访问

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print?

01

02

<?php

03	class Fruit {

04	const CONST_VALUE = 'Fruit Color' ;

05

}

06

07	$classname = 'Fruit' ;

08	echo $classname ::CONST_VALUE; // As of PHP 5.3.0

09

10	echo Fruit::CONST_VALUE;

11

?>

Program List：在类定义外部使用::

01

02

<?php

03	class Fruit {

04	const CONST_VALUE = 'Fruit Color' ;

05

}

06

07	class Apple extends Fruit

08

{

09	public static $color = 'Red' ;

10

11	public static function doubleColon() {

12	echo parent::CONST_VALUE . "\n" ;

13	echo self:: $color . "\n" ;

14

}

15

}

16

17	Apple::doubleColon();

18

?>

程序运行结果：

1	Fruit Color Red

Program List：调用parent方法

01

02

<?php

03	class Fruit

04

{

05	protected function showColor() {

06	echo "Fruit::showColor()\n" ;

07

}

08

}

09

10	class Apple extends Fruit

11

{

12	// Override parent's definition

13	public function showColor()

14

{

15	// But still call the parent function

16	parent::showColor();

17	echo "Apple::showColor()\n" ;

18

}

19

}

20

21	$apple = new Apple();

22	$apple ->showColor();

23

?>

1	Fruit::showColor()

2	Apple::showColor()

Program List：使用作用域限定符

01

02

<?php

03	class Apple

04

{

05	public function showColor()

06

{

07	return $this ->color;

08

}

09

}

10

11	class Banana

12

{

13	public $color ;

14

15	public function __construct()

16

{

17	$this ->color = "Banana is yellow" ;

18

}

19

20	public function GetColor()

21

{

22	return Apple::showColor();

23

}

24

}

25

26	$banana = new Banana;

27	echo $banana ->GetColor();

28

?>

1	Banana is yellow

Program List：调用基类的方法

01

02

<?php

03

04	class Fruit

05

{

06	static function color()

07

{

08	return "color" ;

09

}

10

11	static function showColor()

12

{

13	echo "show " . self::color();

14

}

15

}

16

17	class Apple extends Fruit

18

{

19	static function color()

20

{

21	return "red" ;

22

}

23

}

24

25	Apple::showColor();

26	// output is "show color"!

27

28

?>

1	show color