1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
|
<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision: 332727 $ -->
<sect1 xml:id="language.oop5.abstract" xmlns="http://docbook.org/ns/docbook">
<title>Class Abstraction</title>
<para>
PHP 5 introduces abstract classes and methods. Classes defined as
abstract may not be instantiated, and 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>
<para>
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 a less restricted)
<link linkend="language.oop5.visibility">visibility</link>. For example,
if the abstract method is defined as protected, the function implementation
must be defined as either protected or public, but not private. Furthermore
the signatures of the methods must match, i.e. the type hints and the number
of required arguments must be the same. For example, if the child class
defines an optional argument, where the abstract method's signature does
not, there is no conflict in the signature. This also applies to constructors
as of PHP 5.4. Before 5.4 constructor signatures could differ.
</para>
<example>
<title>Abstract class example</title>
<programlisting role="php">
<![CDATA[
<?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 $class2->prefixValue('FOO_') ."\n";
?>
]]>
</programlisting>
&example.outputs;
<screen>
<![CDATA[
ConcreteClass1
FOO_ConcreteClass1
ConcreteClass2
FOO_ConcreteClass2
]]>
</screen>
</example>
<example>
<title>Abstract class example</title>
<programlisting role="php">
<![CDATA[
<?php
abstract class AbstractClass
{
// Our abstract method only needs to define the required arguments
abstract protected function prefixName($name);
}
class ConcreteClass extends AbstractClass
{
// Our child class may define optional arguments not in the parent's signature
public function prefixName($name, $separator = ".") {
if ($name == "Pacman") {
$prefix = "Mr";
} elseif ($name == "Pacwoman") {
$prefix = "Mrs";
} else {
$prefix = "";
}
return "{$prefix}{$separator} {$name}";
}
}
$class = new ConcreteClass;
echo $class->prefixName("Pacman"), "\n";
echo $class->prefixName("Pacwoman"), "\n";
?>
]]>
</programlisting>
&example.outputs;
<screen>
<![CDATA[
Mr. Pacman
Mrs. Pacwoman
]]>
</screen>
</example>
<para>
Old code that has no user-defined classes or functions named
'abstract' should run without modifications.
</para>
</sect1>
<!-- Keep this comment at the end of the file
Local variables:
mode: sgml
sgml-omittag:t
sgml-shorttag:t
sgml-minimize-attributes:nil
sgml-always-quote-attributes:t
sgml-indent-step:1
sgml-indent-data:t
indent-tabs-mode:nil
sgml-parent-document:nil
sgml-default-dtd-file:"~/.phpdoc/manual.ced"
sgml-exposed-tags:nil
sgml-local-catalogs:nil
sgml-local-ecat-files:nil
End:
vim600: syn=xml fen fdm=syntax fdl=2 si
vim: et tw=78 syn=sgml
vi: ts=1 sw=1
-->
|
