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2010年最新PHP类的精缩归纳
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Jun 14, 2016 am 12:02 AM
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2010年最新PHP类的精缩归纳

 

一:结构和调用(实例化):

class className{} ,调用:$obj = new className();当类有构造函数时,还应传入参数。如$obj = new className($v,$v2...);

二:构造函数和析构函数:

1、构造函数用于初始化:使用__construct(),可带参数。

2、但析构函数不能带参数(用于在销去一个类之前执行一些操作或功能)。析构函数用__destruct()做名称。在脚本执行结束时,PHP会销掉内存中的对象,因此可不用析造函数,但有些比如COOKIE等,就应当要用此函数销掉。

知识点:在PHP4中也提供了构造函数,但使用的是与类同名的类方法,在PHP5仍能兼容这种做法,当一个类中没有包含__construct时,会查找与类同名的方法,如果找到,就认为是构造函数,如下:

class test
{ var $b;
function test() { $this->b=5; }
function addab($c) { return $this->b+$c; }
}
$a = new test(); echo $a->addab(4); // 返回 9

3、PHP不会自动调用父类的构造函数(不支持构造函数重载),必须使用parent关键字显式地调用。

class employee{
function __construct()....
}
class Manager extents Employee{
function __construct(){
parent::_construct();
echo '这个子类的父类构造函数调用了!';
}
}

当然也可以调用与该实例没有任何关系的其它类的构造函数。只需在__construct()前加上类名即可。如:

otherClassName::__construct();

类的主家庭成员:属性、方法、常量、静态成员

三、类的属性:

有两种方法对类的属性赋值或取值。

1、使用公共作用域public关键词。

2、使用__set()和__get()来分别赋值和取值,前者称为设置方法(setter)或修改方法(mutator),后者称为访问方法(accessor)或获取方法(getter)。建议使用这种方法:优点:

A、可在__set()统一进行数据验证。

B、便于统一管理属性。

注意:

第一:__set()和__get()只对私有属性起作用,对于用public定义的属性,它们两个都懒理搭理,如下:

class test{
protected $a=9,$b=2,$c;
public $d;
function __set($n,$v) { $this->$n = $v+2; }
function __get($name) { return $this->$name+2; }
}
$a = new test();
$a->b =5;
echo "
";
echo $a->b;

实例只对$a,$b,$c的设置会经过__set和__get过滤与返回,对于$d,就不会起作用。如$a->d=5,再返回还是5。

第二:__set($n,$v)要带两个参数。而__get($n)只能有一个参数。实例:

class test{
private $a=5,$b=6,$c;
function __set($n,$v)
{
if($n=='a'&&$n>0)
$this->$n = $v;
else
$this->$n = $v+2;
}
function __get($name)
{
return $this->$name; //如果改为return $this->$name + $this->addab(); 如调用a的值,实际返回的是a+a+b的值。默认为5+5+6=16。
}
function addab()
{ return $this->a + $this->b; }
}
$e=new test();
$e->a = 11; //注意写法:类的内部用$this->$n即变量的写法,但外部实例要用$e->a的方式。
$e->b = 12; //get 14
$e->k = 22;

类的属性可自由扩展,如上例的k,不管是否用__set,当一个实例建立起来后,可以用$e->newProperty = xx;直接来创造一个属性,但不建议这么做。

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