PHP面向对象中的重要知识点(三)

1. namespace:

    和C++中的名字空间很像,作用也一样,都是为了避免在引用较多第三方库时而带来的名字冲突问题。通过名字空间,即便两个class的名称相同,但是因为位于不同的名字空间内,他们仍然可以被精确定位和区分。第一次看到PHP的名字空间语法时,感觉和C++相比在语法上是非常非常相似的,然而在写点儿小例子做做实验的时候才发现,他们的差别还是很大的,为了避免以后忘记,所以这里特别将其记录了下来。见如下代码:

<?php
//in Test2.php
namespace nstest\test2;

class Test2 {
    public static function printMe() {
        print 'This is nstest\test2\Test2::printSelf.'."\n";
    }
}

<?php
//in Test1.php
namespace nstest\test1;

class Test1 {
    public static function printMe() {
        print 'This is nstest\test1\Test1::printSelf.'."\n";
    }
}
require "Test2.php";
nstest\test2\Test2::printMe();

    运行结果如下:

bogon:TestPhp$ php Test1.php 
PHP Fatal error:  Class 'nstest\test1\nstest\test2\Test2' not found in /Users/liulei/PhpstormProjects/TestPhp/Test1.php on line 13

    是不是这个结果比较出乎意料,原因在哪呢?HOHO,原来PHP在进行名字空间引用的时候,如果名字空间的第一个字符不是前导斜杠(\),那么就被自动识别为相对名字空间,在上面的代码中,Test1自身所在的名字空间是namespace nstest\test1,因此在以nstest\test2\Test2::printMe()方式调用Test2::printMe()时,PHP将自动解析为nstest\test1\nstest\test2\Test2::printMe(),即认为nstest\test2是在当前名字空间内部的。修正该问题非常简单,只需在引用时加上前导斜杠(\)即可,见以下修复后的代码:     

<?php
//Test2.php
namespace nstest\test2;

class Test2 {
    public static function printMe() {
        print 'This is nstest\test2\Test2::printSelf.'."\n";
    }
}

<?php
//Test1.php
namespace nstest\test1;

class Test1 {
    public static function printMe() {
        print 'This is nstest\test1\Test1::printSelf.'."\n";
    }
}
require "Test2.php";
\nstest\test2\Test2::printMe();

    运行结果如下:

bogon:TestPhp$ php Test1.php 
This is nstest\test2\Test2::printSelf.

    还有一种改动方式,可以示意一下PHP中名字空间中的相对引用。这里我们可以将Test1的名字空间改为namespace nstest,其他的修改见以下代码中红色高亮部分:

<?php
//Test2.php
namespace nstest\test2;

class Test2 {
    public static function printMe() {
        print 'This is nstest\test2\Test2::printSelf.'."\n";
    }
}

<?php
//Test1.php
namespace nstest;

class Test1 {
    public static function printMe() {
        print 'This is nstest\test1\Test1::printSelf.'."\n";
    }
}

require "Test2.php";
test2\Test2::printMe(); 

    运行结果等于上面正确的结果。最重要的差别就是该例使用了PHP名字空间中的相对定位。相信熟悉C++的开发者一定会想到use关键字,PHP也提供了该关键字,他们的功能是一致的,都是为了避免在后面的代码中,无需再通过全限定符(类名前加名字空间前缀)来引用其他名字空间中的类了。至于具体的语法规则,还是看看下面具体的代码和关键性注释吧。

<?php
//Test2.php
namespace nstest\test2;

class Test2 {
    public static function printMe() {
        print 'This is nstest\test2\Test2::printSelf.'."\n";
    }
}

<?php
//Test1.php
namespace nstest\test1;

class Test1 {
    public static function printMe() {
        print 'This is nstest\test1\Test1::printSelf.'."\n";
    }
}

require "Test2.php";
//这里需要特别注意的是,nstest\test2已经表示名字空间绝对路径定位,不需要再加前导斜杠(\)了。
//另外这里还有一个隐式规则是test2表示该名字空间的缺省别名,在引用其名字空间内的对象时需要加test2前缀。
use nstest\test2;
test2\Test2::printMe();

//这里我们也可以给名字空间显式的指定别名,如:
use nstest\test2 as test2_alias;
test2_alias\Test2::printMe(); 

    运行结果如下:

bogon:TestPhp$ php Test1.php 
This is nstest\test2\Test2::printSelf.
This is nstest\test2\Test2::printSelf.

    最后介绍一下PHP中全局名字空间的引用方式,见如下代码和关键性注释:

<?php
class Test {
    public static function printMe() {
        print 'This is Global namespace Test::printSelf.'."\n";
    }
}

//下面两行代码表示的是同一对象,即全局名字空间下的Test类,然而如果因为名字空间冲突导致第一种方式不能被PHP
//编译器正常识别,那么就可以使用第二种方式显式的通知PHP,自己要引用的是全局名字空间中的Test类。
Test::printMe();
\Test::printMe();

    运行结果如下:

bogon:TestPhp$ php Test1.php 
This is Global namespace Test::printSelf.
This is Global namespace Test::printSelf.

2. Reflection:

    PHP中的反射和Java中java.lang.reflect包提供的功能一样,更有意思的是,就连很多方法命名和调用方式也是非常雷同的。他们都是由一些列可以分析类、类方法和方法参数的PHP内置类组成。我们这里主要介绍的是如下几个常用的内置类:(Reflection、RelectionClass、ReflectionMethod、ReflectionParameter和ReflectionProperty)。现在我们还是一步一步来理解,即从ReflectionClass开始给出示例代码和关键性注释: 

<?php
class TestClass {
    public $publicVariable;

    function publicMethod() {
        print "This is publicMethod.\n";
    }
}

function classInfo(ReflectionClass $c) {
    $details = "";
    //getName将返回实际的类名。
    $name = $c->getName();
    if ($c->isUserDefined()) {
        $details .= "$name is user defined.\n";
    }
    if ($c->isInternal()) {
        $details .= "$name is built-in.\n";
    }
    if ($c->isAbstract()) {
        $details .= "$name is abstract class.\n";
    }
    if ($c->isFinal()) {
        $details .= "$name is final class.\n";
    }
    if ($c->isInstantiable()) {
        $details .= "$name can be instantiated.\n";
    } else {
        $details .= "$name cannot be instantiated.\n";
    }
    return $details;
}

function classSource(ReflectionClass $c) {
    $path = $c->getFileName();
    $lines = @file($path);
    //获取类定义代码的起始行和截至行。
    $from = $c->getStartLine();
    $to = $c->getEndLine();
    $len = $to - $from + 1;
    return implode(array_slice($lines,$from - 1,$len));
}

print "The following is Class Information.\n";
print classInfo(new ReflectionClass('TestClass'));

print "\nThe following is Class Source.\n";
print classSource(new ReflectionClass('TestClass'));

    运行结果如下:

bogon:TestPhp$ php reflection_test.php 
The following is Class Information.
TestClass is user defined.
TestClass can be instantiated.

The following is Class Source.
class TestClass {
    public $publicVariable;

    function publicMethod() {
        print "This is publicMethod.\n";
    }
}

    下面让我们仍然以代码示例和关键性注释的方法继续ReflectionMethod的学习之旅。

<?php
class TestClass {
    public $publicVariable;

    function __construct() {

    }
    private function privateMethod() {

    }
    function publicMethod() {
        print "This is publicMethod.\n";
    }
    function publicMethod2(string $arg1, int $arg2) {

    }
}

//这个函数中使用的ReflectionMethod中的方法都是非常简单直观的,就不再过多赘述了。
function methodInfo(ReflectionMethod $m) {
    $name = $m->getName();
    $details = "";
    if ($m->isUserDefined()) {
        $details .= "$name is user defined.\n";
    }
    if ($m->isInternal()) {
        $details .= "$name is built-in.\n";
    }
    if ($m->isAbstract()) {
        $details .= "$name is abstract.\n";
    }
    if ($m->isPublic()) {
        $details .= "$name is public.\n";
    }
    if ($m->isProtected()) {
        $details .= "$name is protected.\n";
    }
    if ($m->isPrivate()) {
        $details .= "$name is private.\n";
    }
    if ($m->isStatic()) {
        $details .= "$name is static.\n";
    }
    if ($m->isFinal()) {
        $details .= "$name is final.\n";
    }
    if ($m->isConstructor()) {
        $details .= "$name is constructor.\n";
    }
    if ($m->returnsReference()) {
        $details .= "$name returns a reference.\n";
    }
    return $details;
}

function methodSource(ReflectionMethod $m) {
    $path = $m->getFileName();
    $lines = @file($path);
    $from = $m->getStartLine();
    $to = $m->getEndLine();
    $len = $to - $from + 1;
    return implode(array_slice($lines, $from - 1, $len));
}

$rc = new ReflectionClass('TestClass');
$methods = $rc->getMethods();
print "The following is method information.\n";
foreach ($methods as $method) {
    print methodInfo($method);
    print "\n--------------------\n";
}

print "The following is Method[TestClass::publicMethod] source.\n";
print methodSource($rc->getMethod('publicMethod'));

    运行结果如下:

bogon:TestPhp$ php reflection_test.php 
The following is method information.
__construct is user defined.
__construct is public.
__construct is constructor.

--------------------
privateMethod is user defined.
privateMethod is private.

--------------------
publicMethod is user defined.
publicMethod is public.

--------------------
publicMethod2 is user defined.
publicMethod2 is public.

--------------------
The following is Method[TestClass::publicMethod] source.
    function publicMethod() {
        print "This is publicMethod.\n";
    }

    让我们继续ReflectionParameter吧,他表示的是成员函数的参数信息。继续看代码吧。

<?php
class ParamClass {

}

class TestClass {
    function publicMethod() {
        print "This is publicMethod.\n";
    }
    function publicMethod2(ParamClass $arg1, &$arg2, $arg3 = null) {

    }
}

function paramInfo(ReflectionParameter $p) {
    $details = "";
    //这里的$declaringClass将等于TestClass。
    $declaringClass = $p->getDeclaringClass();
    $name = $p->getName();
    $class = $p->getClass();
    $position = $p->getPosition();
    $details .= "\$$name has position $position.\n";
    if (!empty($class)) {
        $classname = $class->getName();
        $details .= "\$$name must be a $classname object\n";
    }
    if ($p->isPassedByReference()) {
        $details .= "\$$name is passed by reference.\n";
    }
    if ($p->isDefaultValueAvailable()) {
        $def = $p->getDefaultValue();
        $details .= "\$$name has default: $def\n";
    }
    return $details;
}

$rc = new ReflectionClass('TestClass');
$method = $rc->getMethod('publicMethod2');
$params = $method->getParameters();

foreach ($params as $p) {
    print paramInfo($p)."\n";
}

    运行结果如下:

bogon:TestPhp$ php reflection_test.php 
$arg1 has position 0.
$arg1 must be a ParamClass object

$arg2 has position 1.
$arg2 is passed by reference.

$arg3 has position 2.
$arg3 has default: 

    上面介绍的都是通过PHP提供的Reflection API来遍历任意class的具体信息,事实上和Java等其他语言提供的反射功能一样,PHP也同样支持通过反射类调用实际对象的方法,这里将主要应用到两个方法,分别是ReflectionClass::newInstance()来创建对象实例,另一个是ReflectionMethod::invoke(),根据对象实例和方法名执行该方法。见如下代码:

<?php
class TestClass {
    private $privateArg;
    function __construct($arg) {
        $this->privateArg = $arg;
    }
    function publicMethod() {
        print '$privateArg = '.$this->privateArg."\n";
    }

    function publicMethod2($arg1, $arg2) {
        print '$arg1 = '.$arg1.' $arg2 = '.$arg2."\n";
    }
}

$rc = new ReflectionClass('TestClass');
$testObj = $rc->newInstanceArgs(array('This is private argument.'));
$method = $rc->getMethod('publicMethod');
$method->invoke($testObj);

$method2 = $rc->getMethod('publicMethod2');
$method2->invoke($testObj,"hello","world");

    运行结果如下:

bogon:TestPhp$ php reflection_test.php 
$privateArg = This is private argument.
$arg1 = hello $arg2 = world

    事实上ReflectionClass、ReflectionMethod和ReflectionParameter提供给我们的可用方法还有更多,这里只是给出几个最典型的方法,以便我们可以更为直观的学习和了解PHP Reflection API。相信再看完以后的代码示例之后,我们都会比较清楚,如果今后需要用到和class相关的功能,就从ReflectionClass中查找,而member function的信息则一定来自于ReflectionMethod,方法参数信息来自于ReflectionParameter。

注:该Blog中记录的知识点,是在我学习PHP的过程中,遇到的一些PHP和其他面向对象语言相比比较独特的地方,或者是对我本人而言确实需要簿记下来以备后查的知识点。虽然谈不上什么深度,但是还是希望能与大家分享。

posted @ 2014-01-04 09:07  OrangeAdmin  阅读(5873)  评论(0编辑  收藏  举报