介绍PHP面向对象的基础知识
1. 接口的定义interface ,类定义class,类支持abstract和final修饰符，abstract修饰为抽象类，抽象类
不支持直接实例化，final修饰的类/方法不能被继承/方法重写.
2. 接口的实现通过implements,类继承extends
<span>interface</span><span> IShape{
</span><span>function</span><span> draw_core();
};
</span><span>class</span> PathShape <span>implements</span><span> IShape{
</span><span>public</span> <span>function</span><span> draw_core(){}
}
</span><span>class</span> Rectangle <span>extends</span><span> PathShape{
</span><span>public</span> <span>function</span><span> draw_core(){
</span><span>//</span><span>overide draw_core</span>
<span> }
}</span> 3.静态变量和常量(static ,const )
a.常量声明变量名前面不需要加美元修饰符$,静态变量需要
b.两者都通过类访问，静态变量方法时候需要在变量名前加$美元修饰符好
<span>class</span><span> MyClass{
</span><span>const</span><span> M_CONST_VALUE;
</span><span>static</span> <span>$M_STATIC_VALUE</span><span>;
}
MyClass</span>::<span>M_CONST_VALUE ;
MyClass</span>::<span>$M_STATIC_VALUE</span>;c.常量声明时候不支持访问权限修饰符，不能在const前加public，常量默认就是public。
<span>const</span> M_CONST ; <span>//</span><span>OK</span> <span>public</span> <span>const</span> M_CONST ; <span>//</span><span> throw exception</span>
4.类内部访问非静态/常量变量和方法通过$this,访问父类通过parent,在类内部访问静态变量和方法可以通过
self,self本质是指向该类也可以通过static访问
parent::method(); <span>//</span><span>父类方法</span> <span>$this</span>->method() ; <span>//</span><span>方法实例方法</span> self::<span>$static_value</span> ;<span>//</span><span>访问静态变量</span> <span>static</span>::<span>$static_value</span>;<span>//</span><span>同上</span>
5.static和self的区别在于self指的是解析上下文，也是是作用与当前类，static指的是被调用
的类而不是包含类，典型的例子就是单例
<span>abstract</span> <span>class</span><span> ParentClass{
</span><span>public</span> <span>static</span> <span>function</span><span> createInstance(){
</span><span>return</span> <span>new</span> <span>static</span><span>();
</span><span>//</span><span>这里不能使用self,因为self本意其实指向parentclass的
//如果你使用了self，那么将抛出异常，提示抽象类无法实例化
//而static并不直接指向parentclass而是作用与包含类
//</span>
<span> }
}
</span><span>class</span> ChildClass <span>extends</span><span> ParentClass{
</span><span>//
</span> }7.类中使用拦截器,PHP拦截器有__get,__set,__inset,__unset,__call，这里只关注geth和set拦截器
__get(<span>$property</span><span>) 当访问未定义的属性时候该方法被调用
__set(</span><span>$property</span>,<span>$value</span><span>)当给未定义的属性赋值时被调用
</span><span>class</span><span> MyClass{
</span><span>public</span> <span>function</span> __get(<span>$property</span><span>){
</span><span>echo</span> "Access __get"<span>;
</span><span>if</span>(property_exists(<span>$this</span>,<span>$property</span><span>)){
</span><span>return</span> <span>$this</span>-><span>$property</span><span>;
}</span><span>else</span><span>{
</span><span>return</span> "unknown"<span>;
}
}
</span><span>public</span> <span>function</span> __set(<span>$property</span>,<span>$value</span><span>){
</span><span>if</span>(!property_exists(<span>$this</span>,<span>$property</span><span>)){
</span><span>$this</span>->Name = <span>$value</span>; <span>//</span><span>变量不存在就直接给$Name赋值</span>
<span> }
}
</span><span>public</span> <span>$Name</span> = "visonme"<span>;
};
</span><span>//</span><span>访问</span>
<span>$obj</span> = <span>new</span><span> MyClass();
</span><span>$obj</span>->Name ; <span>//</span><span>直接访问变量$Name</span>
<span>$obj</span>->Password;<span>//</span><span>Password未定义，先访问__get最后输出unknown
//-for __set</span>
<span>$obj</span>->password = 'fz-visonme';<span>//</span><span>password不存在，那么将走__setz最后给$Name赋值</span>
<span>echo</span> <span>$obj</span>->Name ; <span>//</span><span> output: fz-visonme</span>8.类构造函数和析构函数:__construct, __destruct ,构造函数实例化对象时候调用，多用于成员变量初始化工作，析构在类销毁时候调用，多用于收尾工作
<span>class</span><span> MyClass{
</span><span>function</span><span> __construct(){}
</span><span>function</span><span> __destruct(){}
}</span>9.对象的复制通过clone，clone关键字使用“值复制"方式来产生一个新的对象,对于对象复制本身还是走引用复制的。
a.简单类型赋值
<span>class</span><span> MyClass{
</span><span>public</span> <span>$ID</span><span>;
};
</span><span>$a</span> = <span>new</span><span> MyClass;
</span><span>$a</span>->ID = 199<span>;
</span><span>$b</span> = <span>clone</span> <span>$a</span><span>;
</span><span>echo</span> <span>$b</span>->ID; <span>//</span><span> output: 199</span>b.包含对象的复制
<span>class</span><span> Account{
</span><span>public</span> <span>$RMB</span><span>;
};
</span><span>class</span><span> MyClass{
</span><span>public</span> <span>$ID</span><span>;
</span><span>public</span> <span>$AccountObj</span><span>;
</span><span>public</span> <span>function</span> __construct(<span>$c</span><span>){
</span><span>$this</span>->AccountObj = <span>$c</span><span>;
}
};
</span><span>$a</span> = <span>new</span> MyClass(<span>new</span><span> Account());
</span><span>$a</span>->AccountObj->RMB= 199<span>;
</span><span>$b</span> = <span>clone</span> <span>$a</span><span>;
</span><span>echo</span> <span>$b</span>->AccountObj->RMB; <span>//</span><span>output: 199</span>
<span>$a</span>->AccountObj->RMB = 100<span>;
</span><span>echo</span> <span>$b</span>->AccountObj->RMB; <span>//</span><span>output: 100</span>
<span>
在clone后，</span><span>$a的AccountObj改变时候</span>，同时会影响到<span>$b</span>这种结果显然不是我们所期望的，我们所期望的是ab是两个不存在任何关联的独立对象.
为了解决这个问题我么可以在类内部实现__clone，当我们在外面调用clone时候其内部会调用类的__clonef方法，所以我们可以通过重写__clone来达到对clone的控制.例如针对b例子的改造
<span>class</span><span> MyClass{
</span><span>public</span> <span>$ID</span><span>;
</span><span>public</span> <span>$AccountObj</span><span>;
</span><span>public</span> <span>function</span> __construct(<span>$c</span><span>){
</span><span>$this</span>->AccountObj = <span>$c</span><span>;
}
</span><span>//</span><span>__clone实现clone的控制
//这里内部同时对Account实现一次clone，这里就可以避免b例子中出现的问题</span>
<span>public</span> <span>function</span><span> __clone(){
</span><span>$this</span>->ID = 0 ; <span>//</span><span>将ID置为0，如果你需要的话</span>
<span>$this</span>->AccountObj = <span>clone</span> <span>$this</span>-><span>AccountObj;
}
};</span>关于__clone方法我们需要知道，该方法是在被clone后的对象上调用，而不是在原始的对象上面运行的，例如上b例子中
$b = clone $a ; //执行的过程： 基本复制对象$a ---> $b执行__clone()
