PHP object-oriented basics (interfaces, classes), PHP is oriented

Introducing the basic knowledge of PHP object-oriented

1. Definition of interface interface, class definition class, class supports abstract and final modifiers, abstract is modified into abstract class, abstract class

Does not support direct instantiation, and final-modified classes/methods cannot be inherited/method overridden.
2. The interface is implemented through implements, and class inheritance 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. Static variables and constants (static, const)
a. There is no need to add the dollar modifier $ in front of the constant declaration variable name, and static variables require
b. Both are accessed through classes, static variable methods Sometimes you need to add the $ dollar modifier before the variable name

   <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. Access permission modifiers are not supported when declaring constants. Public cannot be added before const. Constants default to 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. Access non-static/constant variables and methods within a class through $this, access the parent class through parent, and access static variables and methods within a class through
self. Self essentially points to the class or through static Visit

   parent::method(); <span>//</span><span>父類方法</span>
   <span>$this</span>->method() ; <span>//</span><span>方法實(shí)例方法</span>
   self::<span>$static_value</span> ;<span>//</span><span>訪問靜態(tài)變量</span>
   <span>static</span>::<span>$static_value</span>;<span>//</span><span>同上</span>

5. The difference between static and self is that self refers to the parsing context, which is also the current class. Static refers to the class that is called
rather than the containing class. A typical example is a singleton

 <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>這里不能使用self,因?yàn)閟elf本意其實(shí)指向parentclass的
     //如果你使用了self，那么將拋出異常，提示抽象類無法實(shí)例化
     //而static并不直接指向parentclass而是作用與包含類
     //</span>
<span>   }
 }

 </span><span>class</span> ChildClass <span>extends</span><span> ParentClass{
   </span><span>//
</span> }

7. Use interceptors in classes. PHP interceptors include __get, __set, __inset, __unset, __call. Here we only focus on geth and set interceptors

 __get(<span>$property</span><span>) 當(dāng)訪問未定義的屬性時候該方法被調(diào)用
 __set(</span><span>$property</span>,<span>$value</span><span>)當(dāng)給未定義的屬性賦值時被調(diào)用
 </span><span>class</span><span> MyClass{
    </span><span>public</span> <span>function</span> __get(<span>$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>變量不存在就直接給$Name賦值</span>
<span>      }
    }
    
    </span><span>public</span> <span>$Name</span> = "visonme"<span>;
 };
 </span><span>//</span><span>訪問</span>
 <span>$obj</span>  = <span>new</span><span> MyClass();
 </span><span>$obj</span>->Name ; <span>//</span><span>直接訪問變量$Name</span>
 <span>$obj</span>->Password;<span>//</span><span>Password未定義，先訪問__get最后輸出unknown

 //-for __set</span>
 <span>$obj</span>->password = 'fz-visonme';<span>//</span><span>password不存在，那么將走_(dá)_setz最后給$Name賦值</span>
 <span>echo</span> <span>$obj</span>->Name ; <span>//</span><span> output: fz-visonme</span>

8. Class constructor and destructor: __construct, __destruct. The constructor is called when instantiating an object and is mostly used for member variable initialization. Destructor is called when the class is destroyed and is mostly used for finishing work

<span>class</span><span> MyClass{
  </span><span>function</span><span> __construct(){}
  </span><span>function</span><span> __destruct(){}
}</span>

9. The object is copied through clone. The clone keyword uses the "value copy" method to generate a new object. The object copy itself is still copied by reference.

a. Simple type assignment

<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. Copy of containing objects

<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改變時候</span>，同時會影響到<span>$b</span>

This result is obviously not what we expect. What we expect is that ab is two independent objects without any correlation.

In order to solve this problem, we can implement __clone inside the class. When we call clone outside, the __clonef method of the class will be called internally, so we can achieve control of clone by overriding __clone. For example Modification of example b

<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實(shí)現(xiàn)clone的控制
  //這里內(nèi)部同時對Account實(shí)現(xiàn)一次clone，這里就可以避免b例子中出現(xiàn)的問題</span>
  <span>public</span> <span>function</span><span> __clone(){
    </span><span>$this</span>->ID = 0 ; <span>//</span><span>將ID置為0，如果你需要的話</span>
    <span>$this</span>->AccountObj = <span>clone</span> <span>$this</span>-><span>AccountObj;
  }
};</span>

We need to know about the __clone method. This method is called on the cloned object, not on the original object. For example, in the example b above

$b = clone $a; //Execution process: Basic copy object $a ---> $b executes __clone()