PHP5 is a language that has the characteristics of most object-oriented languages. It has many object-oriented features than PHP4, but some concepts are also quite confusing. So let's talk about it today, sorry. (To read this article, you need to understand PHP5's object-oriented knowledge.) first, let's understand three keywords: this, self, parent, literally compared to "> <LINKhref =" http:
PHP5 is a language that has the characteristics of most object-oriented languages. It has many object-oriented features than PHP4, but some concepts are also quite confusing. So let's talk about it today, sorry. (Read this article to learn about PHP5's object-oriented knowledge)
First, let's take a look at three keywords: this, self, and parent, which are literally easy to understand. It means this: yourself, father, haha, it's fun, let's first establish several concepts. Where are these three keywords used? This is a pointer to the current object (let's look at the pointer in C), self is a pointer to the current class, and parent is a pointer to the parent class.
If we do not know much about this, let's talk about it based on the actual examples. (1) this
{
// Define attributes
Private $ name; // define the constructor
Function _ construct ($ name)
{
$ This-> name = $ name; // this pointer is already used here
} // Destructor
Function _ destruct () {}// print the username member function
Function printName ()
{
Print ($ this-> name); // this pointer is used again
}
} // Instantiate the object
$ NameObject = new UserName ("heiyeluren"); // Print
$ NameObject-> printName (); // output: heiyeluren // The second instantiated object
$ NameObject2 = new UserName ("PHP5"); // Print
$ NameObject2-> printName (); // output: PHP5
?> We can see that the class above uses the this pointer in 11 rows and 20 rows respectively. Who is this pointing? In fact, this is used to determine who to point to During instantiation. For example, when the object is first instantiated (25 rows), then this is to point to the $ nameObject object, then print ($ this->Name), then of course the output is "heiyeluren ". In the second instance, print ($ this-> name) is changed to print ($ nameObject2-> name), so "PHP5" is output ". Therefore, this is a pointer to the current object instance and does not point to any other object or class. (2) self first, we need to make it clear that self points to the class itself, that is, self does not point to any instantiated object. Generally, self points to static variables in the class.
{
// Define attributes, including a static variable
Private static $ firstCount = 0;
Private $ lastCount;
// Constructor
Function _ construct ()
{
$ This-> lastCount = ++ selft: $ firstCount; // Use self to call static variables. To use self to call static variables, you must use: (domain operator number)
}
// Print the maximum value
Function printLastCount ()
{
Print ($ this-> lastCount );
}
} // Instantiate the object
$ CountObject = new Counter ();
$ CountObject-> printLastCount (); // output 1
?>
Here, we only need to pay attention to two places: 6th rows and 12th rows. We defined a static variable $ firstCount in the second row, and the initial value is 0. Therefore, when the value is called in 12 rows, we use self to call the variable, and we use ":" In the middle to connect, which is our so-called domain operator. At this time, we call the static variable $ frestCount defined by the class, our static variables have nothing to do with the instance of the following object. They are only related to the class. So if I call the class itself, we cannot use this for reference. We can use self for reference, because self points to the class itself and has nothing to do with any object instance. In other words, we must also use self to call static members in our class. (3) parent we know that parent is a pointer to the parent class. Generally, we use parent to call the constructor of the parent class.// Base class
Class Animal
{
// Attributes of the base class
Public $ name; // name
// Constructor of the base class
Public function _ construct ($ name)
{
$ This-> name = $ name;
}
}
// Derived class
Class Person extends Animal // Person class inherits Animal class
{
Public $ personSex; // gender
Public $ personAge; // age
// Constructor of the inherited class
Function _ construct ($ personSex, $ personAge)
{
Parent: :__ construct ("heiyeluren"); // uses parent to call the constructor of the parent class.
$ This-> personSex = $ personSex;
$ This-> personAge = $ personAge;
}
Function printPerson ()
{
Print ($ this-> name. "is". $ this-> personSex. ", this year". $ this-> personAge );
}
}
// Instantiate the Person object
$ PersonObject = new Person ("male", "21"); // Print
$ PersonObject-> printPerson (); // output: heiyeluren is male, this year 21?>
We should pay attention to the following details: the member attributes are public, especially for the parent class, to be accessed by the inheritance class through this. We should pay attention to the key points: row 25th: parent: _ construct ("heiyeluren"). In this case, we will use parent to call the constructor of the parent class to initialize the parent class, because the members of the parent class are all public, we can directly use this to call the class in the inheritance class.
