Mobile app interface programming technology - learn to implement other features of the PHP class

• Static static keyword

  static. In a class, the variables or methods marked by it do not belong to any object. Use "::" when accessing. And when calling self in a class, use "self::"
  For example:

<code><span><span><?php </span><span><span>class</span><span>Car</span> {</span><span>private</span><span>static</span><span>$speed</span> = <span>10</span>;

    <span>public</span><span><span>function</span><span>getSpeed</span><span>()</span> {</span><span>return</span><span>self</span>::<span>$speed</span>;
    }

    <span>//在这里定义一个静态方法，实现速度累加10</span><span>public</span><span>static</span><span><span>function</span><span>speedUp</span><span>()</span>
    {</span><span>return</span><span>self</span>::<span>$speed</span> += <span>10</span>;
    }
}

<span>$car</span> = <span>new</span> Car();
Car::speedUp();  <span>//调用静态方法加速</span><span>echo</span><span>$car</span>->getSpeed();  <span>//调用共有方法输出当前的速度值</span></span></span></code>

Static methods can also be called dynamically through variables.

<code><span>$func</span> = <span>'getSpeed'</span>;
<span>$className</span> = <span>'Car'</span>;
<span>echo</span><span>$className</span>::<span>$func</span>();  <span>//动态调用静态方法</span></code>

• Access control

Access control is implemented through the keywords public, protected and private. Class members defined as public can be accessed from anywhere. Class members defined as protected can be accessed by itself and its subclasses and parent classes. Class members defined as private can only be accessed by the class in which they are defined.

Class attributes must be defined as one of public, protected, and private.

Methods in a class can be defined as public, private or protected. If these keywords are not set, the method defaults to public.

If the constructor is defined as a private method, the object is not allowed to be instantiated directly. At this time, it is generally instantiated through static methods. This method is often used in design patterns to control the creation of objects, such as singleton mode. Only one globally unique object is allowed.

<code><span><span>class</span><span>Car</span> {</span><span>private</span><span><span>function</span><span>__construct</span><span>()</span> {</span><span>echo</span><span>'object create'</span>;
    }

    <span>private</span><span>static</span><span>$_object</span> = <span>null</span>;
    <span>public</span><span>static</span><span><span>function</span><span>getInstance</span><span>()</span> {</span><span>if</span> (<span>empty</span>(<span>self</span>::<span>$_object</span>)) {
            <span>self</span>::<span>$_object</span> = <span>new</span> Car(); 
            <span>//内部方法可以调用私有方法，因此这里可以创建对象</span>
        }
        <span>return</span><span>self</span>::<span>$_object</span>;
    }
}
<span>//$car = new Car(); //这里不允许直接实例化对象</span><span>$car</span> = Car::getInstance(); <span>//通过静态方法来获得一个实例</span></code>

• Inheritance

<code><span><span><?php </span><span><span>class</span><span>Car</span> {</span><span>public</span><span>$speed</span> = <span>0</span>; <span>//汽车的起始速度是0</span><span>public</span><span><span>function</span><span>speedUp</span><span>()</span> {</span><span>$this</span>->speed += <span>10</span>;
        <span>return</span><span>$this</span>->speed;
    }
}
<span>//定义继承于Car的Truck类</span><span><span>class</span><span>Truck</span><span>extends</span><span>Car</span>{</span><span>public</span><span><span>function</span><span>speedUp</span><span>()</span> {</span><span>$this</span>->speed = <span>parent</span>::speedUp() + <span>50</span>;
    }
}

<span>$car</span> = <span>new</span> Truck();
<span>$car</span>->speedUp();
<span>echo</span><span>$car</span>->speed;</span></span></code>

• Overloading

Overloading in PHP refers to the dynamic creation of properties and methods, which is achieved through magic methods. The overloading of attributes uses __set, __get, __isset, and __unset to implement assignment, reading, determining whether the attribute is set, and destroying the attribute if it does not exist, respectively.

<code><span><span>class</span><span>Car</span> {</span><span>private</span><span>$ary</span> = <span>array</span>();

    <span>public</span><span><span>function</span><span>__set</span><span>(<span>$key</span>, <span>$val</span>)</span> {</span><span>$this</span>->ary[<span>$key</span>] = <span>$val</span>;
    }

    <span>public</span><span><span>function</span><span>__get</span><span>(<span>$key</span>)</span> {</span><span>if</span> (<span>isset</span>(<span>$this</span>->ary[<span>$key</span>])) {
            <span>return</span><span>$this</span>->ary[<span>$key</span>];
        }
        <span>return</span><span>null</span>;
    }

    <span>public</span><span><span>function</span><span>__isset</span><span>(<span>$key</span>)</span> {</span><span>if</span> (<span>isset</span>(<span>$this</span>->ary[<span>$key</span>])) {
            <span>return</span><span>true</span>;
        }
        <span>return</span><span>false</span>;
    }

    <span>public</span><span><span>function</span><span>__unset</span><span>(<span>$key</span>)</span> {</span><span>unset</span>(<span>$this</span>->ary[<span>$key</span>]);
    }
}
<span>$car</span> = <span>new</span> Car();
<span>$car</span>->name = <span>'汽车'</span>;  <span>//name属性动态创建并赋值</span><span>echo</span><span>$car</span>->name;
</code>

Method overloading is implemented through __call. When a method that does not exist is called, the __call method will be called as a parameter. When a static method that does not exist is called, the __callStatic overload will be used.

<code>lass Car {
    <span>public</span><span>$speed</span> = <span>0</span>;

    <span>public</span><span><span>function</span><span>__call</span><span>(<span>$name</span>, <span>$args</span>)</span> {</span><span>if</span> (<span>$name</span> == <span>'speedUp'</span>) {
            <span>$this</span>->speed += <span>10</span>;
        }
    }
}
<span>$car</span> = <span>new</span> Car();
<span>$car</span>->speedUp(); <span>//调用不存在的方法会使用重载</span><span>echo</span><span>$car</span>->speed;</code>

• Class object comparison

Object comparison, when all attributes of two instances of the same class are equal, you can use the comparison operator "==" to make a judgment. When you need to judge whether two variables are the same When referencing an object, you can use the equality operator "===" to make a judgment.

<code><span><span>class</span><span>Car</span> {</span>
}
<span>$a</span> = <span>new</span> Car();
<span>$b</span> = <span>new</span> Car();
<span>if</span> (<span>$a</span> == <span>$b</span>) <span>echo</span><span>'=='</span>;   <span>//true</span><span>if</span> (<span>$a</span> === <span>$b</span>) <span>echo</span><span>'==='</span>; <span>//false</span></code>

Object copying. In some special cases, you can copy an object through the keyword clone. At this time, the __clone method will be called, and the value of the attribute is set through this magic method.

<code><span><span>class</span><span>Car</span> {</span><span>public</span><span>$name</span> = <span>'car'</span>;

    <span>public</span><span><span>function</span><span>__clone</span><span>()</span> {</span><span>$obj</span> = <span>new</span> Car();
        <span>$obj</span>->name = <span>$this</span>->name;
    }
}
<span>$a</span> = <span>new</span> Car();
<span>$a</span>->name = <span>'new car'</span>;
<span>$b</span> = <span>clone</span><span>$a</span>;
var_dump(<span>$b</span>);
</code>

Object serialization, you can serialize the object into a string through the serialize method, which is used to store or transfer data, and then deserialize the string into an object for use through unserialize when needed.

<code><span><span>class</span><span>Car</span> {</span><span>public</span><span>$name</span> = <span>'car'</span>;
}
<span>$a</span> = <span>new</span> Car();
<span>$str</span> = serialize(<span>$a</span>); <span>//对象序列化成字符串</span><span>echo</span><span>$str</span>.<span>'<br>'</span>;
<span>$b</span> = unserialize(<span>$str</span>); <span>//反序列化为对象</span>
var_dump(<span>$b</span>);
</code>

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