From e497d4d08d6a7e5ee46c6bc36713853c536a6dc7 Mon Sep 17 00:00:00 2001
From: Curt Zirzow <curt@php.net>
Date: Mon, 2 Aug 2004 03:12:59 +0000
Subject: [PATCH] Clarify what an abstract class can and cannot do, with
example.
git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@164916 c90b9560-bf6c-de11-be94-00142212c4b1
---
language/oop5/abstract.xml | 51 +++++++++++++++++++++++++++-----------
1 file changed, 37 insertions(+), 14 deletions(-)
diff --git a/language/oop5/abstract.xml b/language/oop5/abstract.xml
index bc8b050812..d5c336951d 100644
--- a/language/oop5/abstract.xml
+++ b/language/oop5/abstract.xml
@@ -1,13 +1,14 @@
<?xml version="1.0" encoding="iso-8859-1"?>
-<!-- $Revision: 1.2 $ -->
+<!-- $Revision: 1.3 $ -->
<sect1 id="language.oop5.abstract">
<title>Object Abstraction</title>
<para>
- PHP 5 introduces abstract classes and methods. An abstract
- method only declares the method's signature and does not provide an
- implementation. A class that contains abstract methods needs to be declared
- abstract.
+ 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.
</para>
<example>
@@ -15,26 +16,48 @@
<programlisting role="php">
<![CDATA[
<?php
+
abstract class AbstractClass {
- abstract public function test();
-}
-class ImplementedClass extends AbstractClass {
- public function test() {
- echo "ImplementedClass::test() called.\n";
+ /* Force Extending class to define this method */
+ abstract protected function getValue();
+
+ /* Common method */
+ public function print() {
+ print $this->getValue();
}
+
}
-$o = new ImplementedClass;
-$o->test();
+class ConcreteClass1 extends AbstractClass {
+
+ protected function getValue() {
+ return "ConcreteClass1";
+ }
+
+}
+
+class ConcreteClass2 extends AbstractClass {
+
+ protected function getValue() {
+ return "ConcreteClass2";
+ }
+
+}
+
+$class1 = new ConcreteClass1;
+$class1->print();
+
+$class2 = new ConcreteClass2;
+$class2->print();
?>
]]>
</programlisting>
</example>
<para>
- Abstract classes cannot be instantiated. Old code that has no user-defined
- classes or functions named 'abstract' should run without modifications.
+ Old code that has no user-defined classes or functions named
+ 'abstract' should run without modifications.
</para>
</sect1>