Before proceed let's have an idea what is called class. A class is an abstract characteristics of a thing which includes thing's characteristics (properties) plus thing's behavior (operations).
In programming aspect a class contains a list of variables and functions. Variables represent attributes and functions represent what class objects can do.
Every class definition begins with the keyword class, followed by a class name, followed by a pair of curly braces. Within the braces class members and methods are defined. A pseudo-variable $this can be used within the class method which indicates the references to the calling object.
Note that $this variable is available if class method is called after creating a new instance. This can be also another object's instance. Without creating instance, if a method is called directly then $this variable will not be available.
Below is a simple example of usage class in php.
<html>
<body>
<?php
class MyClass1{
function display(){
if(isset ($this)){
echo '$this is defined = ';
echo get_class($this);
echo "<br />";
}else {
echo '$this is not defined.';
echo "<br />";
}
}
}
class MyClass2{
function display2(){
MyClass1::display();
}
}
$myclass1=new MyClass1();
$myclass1->display(); //$this will be available as function is called from an object context.
MyClass1::display(); //As we are not creating instance here so $this will not be available.
$myclass2=new MyClass2();
$myclass2->display2(); //$this will be available as function is called from an object context.
MyClass2::display2(); //As we are not creating instance here so $this will not be available.
?>
</body>
</html>
The output is,
$this is defined = MyClass1
$this is not defined.
$this is defined = MyClass2
$this is not defined.
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