PHP beginner's learning class and object (1) _ PHP Tutorial

PHP beginner's learning class and object (1 ). PHP5 introduces a new object model (ObjectModel ). The PHP object processing method is completely rewritten, allowing better performance and more features. I. basic concepts 1. definition of each class PHP5. a new Object Model is introduced ). The PHP object processing method is completely rewritten, allowing better performance and more features.

I. Basic concepts

1. class

The definition of each class starts with the keyword class followed by the class name. it can be the name of any non-PHP reserved word. Followed by a pair of curly braces, the bread contains class member and method definitions. The pseudo variable $ this can be used when a method is called inside the object. $ This is a reference to the calling object (usually the object of the method, but it can also be another object, if the method is called statically from the second object. Take the following example:

Example #1 $ this variable in object-oriented language

 
 

  
  
 
  
  
class A 
  
  
{ 
  
  
function foo() 
  
  
{ 
  
  
if (isset($this)) { 
  
  
echo '$this is defined ('; 
  
  
echo get_class($this); 
  
  
echo ")n"; 
  
  
} else { 
  
  
echo "$this is not defined.n"; 
  
  
} 
  
  
} 
  
  
} 
  
  
class B 
  
  
{ 
  
  
function bar() 
  
  
{ 
  
  
A::foo(); 
  
  
} 
  
  
} 
  
  
$a = new A(); 
  
  
$a->foo(); 
  
  
A::foo(); 
  
  
$b = new B(); 
  
  
$b->bar(); 
  
  
B::bar(); 
  
  
?> 
 
 

The above example will output:

 
 

  
  
$this is defined (a) 
  
  
$this is not defined. 
  
  
$this is defined (b) 
  
  
$this is not defined. 
 
 

Example #2 simple class definition

 
 

  
  
 
  
  
Class SimpleClass
  
  
{
  
  
// Member declaration
  
  
Public $ var = 'A default value ';
  
  
// Method declaration
  
  
Public function displayVar (){
  
  
Echo $ this-> var;
  
  
}
  
  
}
  
  
?>
 
 

Example # default value of Class 3 members

 
 

  
  
 
  
  
Class SimpleClass
  
  
{
  
  
// Invalid class member definition:
  
  
Public $ var1 = 'hello'. 'world ';
  
  
Public $ var2 = < 
  
  
Hello world
  
  
EOD;
  
  
Public $ var3 = 1 + 2;
  
  
Public $ var4 = self: myStaticMethod ();
  
  
Public $ var5 = $ myVar;
  
  
// Correct class member definition:
  
  
Public $ var6 = myConstant;
  
  
Public $ var7 = self: classConstant;
  
  
Public $ var8 = array (true, false );
  
  
}
  
  
?>
 
 

2. new

To create an instance of an object, you must create a new object and assign it to a variable. This object is always assigned a value when a new object is created, unless the object defines the constructor and throws an exception when an error occurs.

Example #4 Create an instance

 
 

  
  
 
  
  
$instance = new SimpleClass(); 
  
  
?> 
 
 

When you assign an instance created by an object to a new variable, the new variable accesses the same instance, which is the same as the value assigned by this object. This behavior is the same as when the function is passed into the instance. You can create a new instance by cloning it to a created object.

Example #5 assign values to objects

 
 

  
  
 
  
  
$assigned = $instance; 
  
  
$reference =& $instance; 
  
  
$instance->var = '$assigned will have this value'; 
  
  
$instance = null; // $instance and $reference become null 
  
  
var_dump($instance); 
  
  
var_dump($reference); 
  
  
var_dump($assigned); 
  
  
?> 
 
 

The above example will output:

 
 

  
  
NULL 
  
  
NULL 
  
  
object(SimpleClass)#1 (1) { 
  
  
["var"]=> 
  
  
string(30) "$assigned will have this value" 
  
  
} 
 
 

3. extends

A class can inherit the methods and members of another class with the extends keyword in the declaration. You cannot expand multiple classes and can inherit only one base class.

The inherited methods and members can be overwritten by re-declaring with the same name, unless the final keyword is used when the parent class defines the method. You can use parent: To access covered methods or members.

Example #6 simple class inheritance

 
 

  
  
 
  
  
class ExtendClass extends SimpleClass 
  
  
{ 
  
  
// Redefine the parent method 
  
  
function displayVar() 
  
  
{ 
  
  
echo "Extending classn"; 
  
  
parent::displayVar(); 
  
  
} 
  
  
} 
  
  
$extended = new ExtendClass(); 
  
  
$extended->displayVar(); 
  
  
?> 
 
 

The above example will output:

 
 

  
  
Extending class 
  
  
a default value 
 
 

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