method_exists()

(PHP 4, PHP 5, PHP 7)

检查类的方法是否存在

说明

检查类的方法是否存在于指定的$object中。

参数

对象示例或者类名。

方法名。

返回值

如果$method_name所指的方法在$object所指的对象类中已定义，则返回TRUE，否则返回FALSE。

注释

如果此类不是已知类，使用此函数会使用任何已注册的autoloader。

范例

Example #1method_exists()例子

以上例程会输出：

bool(true)

Staticmethod_exists()例子

以上例程会输出：

bool(true)

参见

• function_exists() 如果给定的函数已经被定义就返回 TRUE
• is_callable() 检测参数是否为合法的可调用结构
• class_exists() 检查类是否已定义

As noted [elsewhere] method_exists() does not care about the existence of __call(), whereas is_callable() does: 

A couple of the older comments (specifically "jp at function dot fi" and "spam at majiclab dot com") state that is_callable() does not respect a methods visibility when checked outside of that class. ie. That private/protected methods are seen as callable when tested publicly. However, this was a bug (#29210) in early versions of PHP 5 and was fixed (according to the changelog) in PHP 5.0.5 (and/or PHP 5.1.0).
Bug #29210 - Function: is_callable - no support for private and protected classes
http://bugs.php.net/29210
Changelog - Fixed bug #29210 (Function: is_callable - no support for private and protected classes). (Dmitry)
http://php.net/ChangeLog-5.php#5.1.0

The function does not care about class existance, so you can use it to check an existance of a method even when class was not declared e.g.

...raises no errors/warnings... outputs "nope, it is not there..." if class does not exist at all or if it does but the method doesn't.

Just to mention it: both method_exists() and is_callable() return true for inherited methods: 

This function is case-insensitive (as is PHP) and here is the proof: 

if you want to check for a method "inside" of a class use:
method_exists($this, 'function_name')
i was a bit confused 'cause i thought i'm only able to check for a method when i got an object like $object_name = new class_name() with: 
method_exists($object_name, 'method_name')
small example for those who didn't understood what i mean ( maybe caused by bad english :) ):

the output will be: a::test() exists!
maybe this will help someone

Note that prepending the namespace (if any) is required even if the calling class is in the same namespace: 

It wasn't spelled out but could be inferred: method_exists() also works on interfaces. 

Note that in PHP5, method_exists() will sucessfully find *private* methods. This has some OO/data-hiding ramifications.

If you want to check in a class itself if a method is known you may do so with magic variable __CLASS__

You might also use the method describe below with  trick but I consider this one here easier and more readable and well, the way it is intended toi be done ;)

Undocumented change since 7.4.0 is released: 

a little difference :
to find a method of an object (instance of a class)

to find a method of a class (using the class name, not the instance of the class!) 

As mentioned before, is_callable and method_exists report all methods callable even if they are private/protected and thus actually not callable. So instead of those functions you may use following work-around which reports methods as supposed to.

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