How to declare Abstract Class?

Question

I am trying to make abstract method clear to me , so I wrote this code and test it. But when I run it the following error appear :

Fatal error: Class Book contains 1 abstract method and must therefore be declared abstract or implement the remaining methods (Book::ClassName) in C:\AppServ\www\index2.php on line 5

so where is the problem and why ?

<?php
  class Book
{
     abstract public function ClassName();
}

 class firstBook extends Book{
    public function ClassName()
    {
        echo "Called form class firstBook";
    }

}

 class secondBook extends Book{
    public function ClassName() 
    {
        echo "Called from class secondBook";
    }
}
$o = new firstBook();
$o2 = new secondBook();
$o->Classname();
$o2->Classname();
?>

you must make class to abstract to declare function as abastract — Satish Sharma, Feb 03 '14 at 06:50

score 1 · Answer 1 · answered Feb 03 '14 at 06:49

1

You cannot declare abstract function in a concrete class. Update your Book class to be abstract.

abstract class Book
{
     abstract public function ClassName();
}

answered Feb 03 '14 at 06:49

vee

38,255
7
74
78

score 1 · Accepted Answer · answered Feb 03 '14 at 06:49

1

Class must also use abstract keyword

<?php
  abstract  class Book
{
     abstract public function ClassName();
}

 class firstBook extends Book{
    public function ClassName()
    {
        echo "Called form class firstBook";
    }

}

 class secondBook extends Book{
    public function ClassName() 
    {
        echo "Called from class secondBook";
    }
}

answered Feb 03 '14 at 06:49

Basic Bridge

1,881
4
25
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hmm , so what if i have to call a variable or a function from class Book ? if it became abstract i can't do that right ? – Anasoft Feb 03 '14 at 06:53
No, if you make a function ( `method` ) in `class Book` it will not become abstract. But it is good to declare all the function that you are going to use in `abstract` class and follow the contract – Basic Bridge Feb 03 '14 at 06:56

Shankar Narayana Damodaran · Answer 3 · 2014-02-03T07:02:59.233

You class has to be abstract.

Change

class Book

to

abstract class Book

Also, you are calling the functions wrongly.

Replace

$o->Classname;
$o2->Classname;

to

$o->ClassName();
$o2->ClassName();

Putting it all together

<?php
abstract class Book
{
    abstract public function ClassName();
}

class firstBook extends Book{
    public function ClassName()
    {
        echo "Called form class firstBook";
    }

}

class secondBook extends Book{
    public function ClassName()
    {
        echo "Called from class secondBook";
    }
}
$o = new firstBook;
$o2 = new secondBook;
$o->ClassName();
$o2->ClassName();
?>

OUTPUT :

Called form class firstBookCalled from class secondBook

How to declare Abstract Class?

3 Answers3

Putting it all together