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Extending Yourself - PHP

Classes and objects are powerful OOP concepts - and PHP4 supportsthem too. This article explains some basic OO entities (including classes,constructors and extensibility) with examples of a table builder and aguestbook.

  1. Back To Class
  2. Who Needs Class, Anyway?
  3. If Wishes Were Prancing Horses...
  4. New Cars For Old
  5. Ford's Law
  6. Turning The Tables
  7. Under Construction
  8. Extending Yourself
  9. Be My Guest
By: icarus, (c) Melonfire
Rating: starstarstarstarstar / 9
October 05, 2000

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Two of the best things about OOP are extensibility and inheritance. Very simply, this means that you can create a new class based on an existing class, add new features (read properties and methods) to it, and then create objects based on this new class. These objects will contain all the features of the original parent class, together with the new features of the child class.

As an illustration, consider the following evenBetterTable class, which adds support for cell spacing and borders.

<? class Table { // constructor function Table() { $this->rows = 4; $this->columns = 5; $this->bcolor = "black"; $this->fcolor = "white"; $this->font = "Times New Roman"; } // set the rows and columns function setGrid($rows, $columns) { $this->rows = $rows; $this->columns = $columns; } // set the colours and fonts function setInterface($bcolor, $fcolor, $font) { $this->bcolor = $bcolor; $this->fcolor = $fcolor; $this->font = $font; } // draw the table function drawTable() { echo "<table cellspacing=" . $this->spacing . " border=" . $this->bsize . " bgcolor=" . $this->bcolor . ">"; for ($x=1; $x<=$this->rows;$x++) { echo "<tr>"; for ($y=1; $y<=$this->columns;$y++) { echo "<td><font face=\"" . $this->font . "\" color=" . $this->fcolor . ">" . $x . ", " . $y . "</font></td>"; } echo "</tr>"; } echo "</table>"; } } class evenBetterTable extends Table { // set cell spacing function setSpacing($space) { $this->spacing = $space; } // set borders function setBorder($size) { $this->bsize = $size; } } ?>
The "extends" keyword is used to extend a parent class to a child class. All the functions and variables of the parent class immediately become available to the child class.

And here's how you could use it:

<? // this is a PHP page which demonstrates extensibility and inheritance // include the class definition include("tables.inc"); ?> <html> <head> <basefont face=Arial> </head> <body> <? // first table $alpha = new evenBetterTable; $alpha->setGrid(4,4); $alpha->setInterface("yellow", "black", "Arial Black"); $alpha->setSpacing(10); $alpha->setBorder(2); $alpha->drawTable(); ?> </body> </html>

>>> More PHP Articles          >>> More By icarus, (c) Melonfire

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