PHP Classes For Beginners

saravanan · #41 (**permalink**) 04-29-2008, 07:06 AM

what is inheritance

saravanan · #42 (**permalink**) 04-30-2008, 06:37 AM

exampe for simple inheritance in php?

jegan · #43 (**permalink**) 04-30-2008, 06:39 AM

PHP Code:

  <?php

class A {

    function example() {

        echo "I am A::example() and provide basic functionality.<br />\n";

    }

}

 
class B extends A {

    function example() {

        echo "I am B::example() and provide additional functionality.<br />\n";

        parent: example();

    }

}

 
$b = new B;

 
// This will call B::example(), which will in turn call A::example().

$b->example();

?>

saravanan · #44 (**permalink**) 04-30-2008, 06:42 AM

Example for multi level inheritance?

jegan · #45 (**permalink**) 04-30-2008, 06:43 AM

PHP Code:

  <?php

 
 
class A {

      function X() {

        echo 'y';

      }

    }

    

    class B extends A{

      function X() {

        echo 'z';

      }

      

      function Y() {

        echo parent::X();

      }

    }

    

    class C extends B {

      function Z () {

        echo parent::Y();

      }

    }

 
$c = new C();

$c->Z();                  //output is 'y'

?>

 
?>

saravanan · #46 (**permalink**) 04-30-2008, 06:46 AM

how can acheive multiple inheritance in php?

jegan · #47 (**permalink**) 05-05-2008, 06:45 AM

Multiple inheritance not achieve directly. but multiple inheritance achieved in some other way is trait and use keywords. Trait act like class and use act like extends.

PHP Code:

  <?php

trait Hello {

  public function sayHello() {

    echo 'Hello ';

  }

}

 
trait World {

  public function sayWorld() {

    echo ' World';

  }

}

 
class MyHelloWorld {

  use Hello, World;

  public function sayExclamationMark() {

    echo '!';

  }

}

 
$o = new MyHelloWorld();

$o->sayHello();

$o->sayWorld();

$o->sayExclamationMark();

// Results eventually in: Hello World!

saravanan · #48 (**permalink**) 05-05-2008, 06:46 AM

what is use parent keyword in php?

jegan · #49 (**permalink**) 05-05-2008, 06:48 AM

You may find yourself writing code that refers to variables and functions in base classes. This is particularly true if your derived class is a refinement or specialisation of code in your base class.
Instead of using the literal name of the base class in your code, you should be using the special name parent, which refers to the name of your base class as given in the extends declaration of your class. By doing this, you avoid using the name of your base class in more than one place. Should your inheritance tree change during implementation, the change is easily made by simply changing the extends declaration of your class.

PHP Code:

  <?php

class A {

    function example() {

        echo "I am A::example() and provide basic functionality.<br />\n";

    }

}

 
class B extends A {

    function example() {

        echo "I am B::example() and provide additional functionality.<br />\n";

        parent::example();

    }

}

 
$b = new B;

 
// This will call B::example(), which will in turn call A::example().

$b->example();

?>

saravanan · #50 (**permalink**) 05-05-2008, 06:49 AM

What is use Scope Resolution Operator in php?

jegan · #51 (**permalink**) 05-05-2008, 06:52 AM

Sometimes it is useful to refer to functions and variables in base classes or to refer to functions in classes that have not yet any instances. The :: operator is being used for this.

PHP Code:

  <?php

class A {

    function example() {

        echo "I am the original function A::example().<br />\n";

    }

}

 
class B extends A {

    function example() {

        echo "I am the redefined function B::example().<br />\n";

        A::example();

    }

}

 
// there is no object of class A.

// this will print

//   I am the original function A::example().<br />

A::example();

 
// create an object of class B.

$b = new B;

 
// this will print 

//   I am the redefined function B::example().<br />

//   I am the original function A::example().<br />

$b->example();

?>

The above example calls the function example() in class A, but there is no object of class A, so that we cannot write $a->example() or similar. Instead we call example() as a 'class function', that is, as a function of the class itself, not any object of that class.

There are class functions, but there are no class variables. In fact, there is no object at all at the time of the call. Thus, a class function may not use any object variables (but it can use local and global variables), and it may not use $this at all.

In the above example, class B redefines the function example(). The original definition in class A is shadowed and no longer available, unless you are referring specifically to the implementation of example() in class A using the ::-operator. Write A::example() to do this (in fact, you should be writing parent::example(), as shown in the next section).

In this context, there is a current object and it may have object variables. Thus, when used from WITHIN an object function, you may use $this and object variables.

saravanan · #52 (**permalink**) 05-06-2008, 06:40 AM

What are abstract Classes in PHP?

saravanan · #53 (**permalink**) 05-07-2008, 05:52 AM

how define and use abstract class in php?

jegan · #54 (**permalink**) 05-07-2008, 05:59 AM

Answer for abstract class:

An abstract class is a class that cannot (or should not) be instantiated. They are surprisingly useful for certain purposes.

2. In PHP a class is merely a set of statements that perform a specific task, and its definition contains both properties and methods, which act as the blueprint from which to create –- or instantiate -– independent objects.
If can’t create objects from a class then what is the use of that classes?

You’re developing an application where different classes are organized in a well-structured hierarchy. On top of this hierarchical relationship, you can define an abstract base class, which exposes a given number of generic properties and methods, in order to model the characteristics and behaviors of all its child classes.

From a purist point of view, this abstract class shouldn’t provide any explicit definition for its methods or properties. These methods and properties should be specifically defined within the subclasses, which automatically would inherit them from the base class. Indeed, this is a powerful concept that can be very useful when applied in the appropriate development context

jegan · #55 (**permalink**) 05-07-2008, 06:03 AM

Answer for how to define and use abstract class :

PHP 5 introduces abstract classes and methods. It is not allowed to create an instance of a class that has been defined as abstract. Any class that contains at least one abstract method must also be abstract. Methods defined as abstract simply declare the method's signature they cannot define the implementation.

When inheriting from an abstract class, all methods marked abstract in the parent's class declaration must be defined by the child; additionally, these methods must be defined with the same (or weaker) visibillity. For example, if the abstract method is defined as protected, the function implementation must be defined as either protected or public.

Abstract class example

PHP Code:

  <?php

abstract class AbstractClass

{

    // Force Extending class to define this method

    abstract protected function getValue();

    abstract protected function prefixValue($prefix);

 
    // Common method

    public function printOut() {

        print $this->getValue() . "\n";

    }

}

 
class ConcreteClass1 extends AbstractClass

{

    protected function getValue() {

        return "ConcreteClass1";

    }

 
    public function prefixValue($prefix) {

        return "{$prefix}ConcreteClass1";

    }

}

 
class ConcreteClass2 extends AbstractClass

{

    public function getValue() {

        return "ConcreteClass2";

    }

 
    public function prefixValue($prefix) {

        return "{$prefix}ConcreteClass2";

    }

}

 
$class1 = new ConcreteClass1;

$class1->printOut();

echo $class1->prefixValue('FOO_') ."\n";

 
$class2 = new ConcreteClass2;

$class2->printOut();

echo $class2->prefixValue('FOO_') ."\n";

?>

The above example will output:

ConcreteClass1
FOO_ConcreteClass1
ConcreteClass2
FOO_ConcreteClass2

saravanan · #56 (**permalink**) 05-07-2008, 06:06 AM

what is interface method?

jegan · #57 (**permalink**) 05-07-2008, 06:15 AM

interfaces allow you to create code which specifies which methods a class must implement, without having to define how these methods are handled.

Interfaces are defined using the interface keyword, in the same way as a standard class, but without any of the methods having their contents defined.

All methods declared in an interface must be public, this is the nature of an interface.

implements
To implement an interface, the implements operator is used. All methods in the interface must be implemented within a class; failure to do so will result in a fatal error. Classes may implement more than one interface if desired by separating each interface with a comma.

chetan1 · #58 (**permalink**) 05-08-2008, 03:14 AM

hi
Ur tutorial of PHP based on the object oriented programming is good. You should proceed ahead regarding cookies and sessions.

saravanan · #59 (**permalink**) 05-08-2008, 06:54 AM

how to define interface in php?

sureshbabu · #60 (**permalink**) 05-08-2008, 07:04 AM

Object Interfaces

Object interfaces allow you to create code which specifies which methods a class must implement, without having to define how these methods are handled.

Interfaces are defined using the interface keyword, in the same way as a standard class, but without any of the methods having their contents defined.