__Construct在OOP类中？ [关闭]

Question

I am newish to the OOP style of PHP5, I have noticed __construct and __deconstruct within example classes and production classes.

I have read over the manual of this:

http://php.net/manual/en/language.oop5.decon.php

and looked over a range of questions/answers on StackOverflow. I'm still having trouble to understand what is the actual meaning of its exisitance?

class foo {
   function __construct()
   {
     // do something 
   }

   public function Example ()
   {
    echo "Example Functions";
   }

   function __destruct()
   {
     // do something
   }
}

The same class can function the same with no hits as:

class foo {
       public function Example ()
       {
        echo "Example Functions";
       }
    }

But the manual states with the above example, that my first function will take over the role as the __construct

Why is this a priority within PHP5 OOP Classes?

Answer 1

class Foo {
    public function __construct() {
        print("This is called when a new object is created");
        // Good to use when you need to set initial values,
        // (possibly) create a connection to a database or such.
    }

    public function __destruct() {
        print("This is called when the class is removed from memory.");
        // Should be used to clean up after yourself, close connections and such.
    }
}

$foo = new Foo();

Addition,

class Person {

    private $name; // Instance variable
    private $status; // Instance variable

    // This will be called when a new instance of this class i created (constructed)
    public function __construct($name, $age) {
        $this->name = ucfirst($name); // Change input to first letter uppercase.

        // Let the user of our class input something he is familiar with,
        // then let the constructor take care of that data in order to fit
        // our specific needs.
        if ($age < 20) {
            $this->status = 'Young';
        } else {
            $this->status = 'Old';
        }
    }

    public function printName() {
        print($this->name);
    }

    public function printStatus() {
        print($this->status);
    }
}

$Alice = new Person('alice', 27);
$Alice->printName();
$Alice->printStatus();

/Addition

If you run the above code and read the comments you should be able to understand when and how constructors and destructors should be used.