Code about some methods and function applications in PHP object-oriented

This article mainly introduces some knowledge points about PHP object-oriented, which has certain reference value. Now I share it with everyone. Friends in need can refer to it

1. __construct:

Built-in constructor, automatically called when the object is created. See the following code:

arg1 = $arg1;
        $this->arg2 = $arg2;
        print "__construct is called...\n";
    }
    public function printAttributes() {
        print '$arg1 = '.$this->arg1.' $arg2 = '.$this->arg2."\n";
    }
}
$testObject = new ConstructTest("arg1","arg2");
$testObject->printAttributes();

The running results are as follows:

Stephens-Air:Desktop$ php Test.php 
__construct is called...
$arg1 = arg1 $arg2 = arg2

2. parent:

Used to directly call the parent class in the subclass Method, function is equivalent to super in Java.

arg1 = $arg1;
        $this->arg2 = $arg2;
        print "__construct is called...\n";
    }
    function getAttributes() {
        return '$arg1 = '.$this->arg1.' $arg2 = '.$this->arg2;
    }
}
 
class SubClass extends BaseClass {
    protected $arg3;
 
    function __construct($baseArg1, $baseArg2, $subArg3) {
        parent::__construct($baseArg1, $baseArg2);
        $this->arg3 = $subArg3;
    }
    function getAttributes() {
        return parent::getAttributes().' $arg3 = '.$this->arg3;
    }
}
$testObject = new SubClass("arg1","arg2","arg3");
print $testObject->getAttributes()."\n";

The running results are as follows:

Stephens-Air:Desktop$ php Test.php 
__construct is called...
$arg1 = arg1 $arg2 = arg2 $arg3 = arg3

3. self:

Call the prefix modification of the static members and static methods of the class within the class, for Non-static member variables and functions use this.

 The running results are as follows: 
Stephens-Air:Desktop$ php Test.php 
Hello, This is static field.
Hello, This is static field.
4. static:
 The static keyword introduced here is mainly used for PHP 5.3 or above. Delayed static binding functionality. Please take a look at the code and critical comments. 
printSelf();
SubB::getInstance()->printSelf();
The running results are as follows: 
Stephens-Air:Desktop$ php Test.php 
This is SubA::printSelf.
This is SubB::printSelf.
 The static keyword can not only be used for instantiation. Like self and parent, static can also be used as an identifier for static method calls, even from non-static contexts. In this scenario, self still represents the class where the current method is located. See the following code: 
ownedGroup = static::getGroup();
    }
    public function printGroup() {
        print "My Group is ".$this->ownedGroup."\n";
    }
    public static function getInstance() {
        return new static();
    }
    public static function getGroup() {
        return "default";
    }
}
 
class SubA extends Base {
}
 
class SubB extends Base {
    public static function getGroup() {
        return "SubB";
    }
}
 
SubA::getInstance()->printGroup();
SubB::getInstance()->printGroup();
The running result is as follows: 
Stephens-Air:Desktop$ php Test.php 
My Group is default
My Group is SubB
5. __destruct:
 The function of the destructor method and The constructor method __construct is just the opposite. It is only called automatically before the object is collected by the garbage collector. We can use this method to do some necessary cleanup work. 
The running results are as follows: 
Stephens-Air:Desktop$ php Test.php 
TestClass destructor is called.
Application will exit.
6. __clone:
     在PHP 5之后的版本中，对象之间的赋值为引用赋值，即赋值后的两个对象将指向同一地址空间，如果想基于对象赋值，可以使用PHP提供的clone方法。该方法将当前对象浅拷贝之后的副本返回，如果想在clone的过程中完成一些特殊的操作，如深拷贝，则需要在当前类的声明中实现__clone方法，该方法在执行clone的过程中会被隐式调用。另外需要格外注意的是，__clone方法是作用再被拷贝的对象上，即赋值后的对象上执行。
id."\n";
    }
}
 
class OuterClass {
    public $innerClass;
    public function __construct() {
        $this->innerClass = new InnerClass();
    }
    public function __clone() {
        $this->innerClass = clone $this->innerClass;
        print "__clone is called.\n";
    }
}
 
$outerA = new OuterClass();
print "Before calling to clone.\n";
$outerB = clone $outerA;
print "After calling to clone.\n";
$outerA->innerClass->id = 20;
print "In outerA: ";
$outerA->innerClass->printSelf();
print "In outerB: ";
$outerB->innerClass->printSelf();
 运行结果如下：
Stephens-Air:Desktop$ php Test.php 
Before calling to clone.
__clone is called.
After calling to clone.
In outerA: $id = 20
In outerB: $id = 10
7. const:
    PHP5可以在类中定义常量属性。和全局常量一样，一旦定义就不能改变。常量属性不需要像普通属性那样以$开头，按照惯例，只能用大写字母来命名常量。另外和静态属性一样，只能通过类而不能通过类的实例访问常量属性，引用常量时同样也不需要以$符号作为前导符。另外常量只能被赋值为基础类型，如整型，而不能指向任何对象类型。
运行结果如下：
0Stephens-Air:Desktop$ php Test.php 
TestClass::AVAILABLE = 0
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