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diff --git a/reference/CPLUSPLUS/CONCEPT/inheritance.html b/reference/CPLUSPLUS/CONCEPT/inheritance.html new file mode 100644 index 0000000..0c8822c --- /dev/null +++ b/reference/CPLUSPLUS/CONCEPT/inheritance.html @@ -0,0 +1,264 @@ +<html> +<head> +<title>Inheritance</title> +</head> +<body bgcolor="#dddddd"> +<font color=brown> +<hr> +<center><h1>Inheritance.</h1></center> +<hr> +<p> +Inheritance enables classes to use the properties of other classes and +add to those properties. +<p> +The thing to remember about object programming is that it attempts to +create a software model as close to the real world as possible. Inheritance +forms an important role to meet this need. Take the following example. +<p> +A fabric can have a colour and size and it is also used to make clothes +as well as tents. Now looking at this from the other angle tents are made +from fabric and poles but clothes are made from fabric and buttons. +So, Tents and clothes have something in common, <blink>fabric!</blink> If we described +tents and clothes in C++, we can seperate fabric into a seperate class +that the Tent and Clothes classes can inherit. +<p> +<center> +<table border="1" bgcolor=ivory width=80%> +<tr align=center> +<td> +<pre> + + ----------- + | Fabric | + ----------- + A A + | | + --- --- + | | + --------- ----------- +| Tent | | Clothes | + --------- ----------- + + +</pre> +</tr> +</td> +</table> +</center> +<p> +Now for some buzz words: +<ol> +<li>Fabric is a <b>base class</b> +<li>Tent and Clothes are <b>derived classes</b> +</ol> +This is what the code looks like: +<p> +<center> +<table border="1" bgcolor=ivory width=50%> +<tr> +<td> +<pre> + +// ... The <b>base</b> class 'Fabric' +// ... is no different to normal. +</pre> +</td></tr> +<tr><td> +<pre> + + class Fabric + { + public: + + Fabric() {}; + ~Fabric() {}; + + SetSize(int x, int y) + { + Length = x; + Width = y; + }; + + SetColour(char *C) + { + strcpy(Colour, C); + } + + private: + int Length; + int Width; + char Colour[20]; + }; + +</pre> +</tr> +</td> +</table> +</center> +<p> + +<center> +<table bgcolor=ivory width=80% border="1"> +<tr> +<td> +<pre> + +// ... The <b>derived</b> class 'Tent' +// ... names 'Fabric' as a base class. +</pre> +</td> +<td> +<pre> + +// ... The <b>derived</b> class 'Clothes' also +// ... names 'Fabric' as a base class. +</pre> +</td> +</tr> +<tr><td> +<pre> + + class Tent <font color=red>: public Fabric</font> + { + public: + + Tent() {}; + ~Tent() {}; + + SetNumOfPoles(int P) + { + Poles = P; + }; + + private: + int Poles; + }; + +</pre> +</td> +<td> +<pre> + + class Clothes <font color=red>: public Fabric</font> + { + public: + + Clothes() {}; + ~Clothes() {}; + + SetNumOfButtons(int B) + { + Buttons = B; + }; + + private: + int Buttons; + }; + +</pre> +</tr> +</td> +</table> +</center> +<p> + +What we now have are three classes with the following public methods. + +<ul> +<li>Fabric +<ol> +<li>SetSize +<li>SetColour +</ol> +<li>Tents +<ol> +<li>SetSize +<li>SetColour +<li>SetNumOfPoles +</ol> +<li>Clothes +<ol> +<li>SetSize +<li>SetColour +<li>SetNumOfButtons +</ol> +</ul> + + +<h2>Using the classes</h2> + +So we have three classes, they are used in the same way as before but +with one extra feature. +<p> +Consider this piece of code. + + +<center> +<table border="1" bgcolor=ivory width=50%> +<tr> +<td> +<pre> + void Init(Fabric &Material); + + main() + { + Tent Frame; + Clothes Jacket; + + Init(Frame); + Init(Jacket); + } + + void Init(Fabric &Material) + { + Material.SetColour("Red"); + Material.SetSize (10, 20); + } + +</pre> +</tr> +</td> +</table> +</center> +<p> + +The function 'Init' expects an object of type 'Fabric' but we +are passing objects of type 'Tents' and 'Clothes', this is OK as +'Tents' and 'Clothes' are derived from Fabric. + +<p> +<hr> +<h2>Examples:</h2> +<img src="../../GRAPHICS/computer.gif" alt="o"> +<a href="../EXAMPLES/inherit.cc">The final program.</a> +<p> + +<hr> +<h2>See Also:</h2> + + +<hr> +<p> +<center> +<table border=2 width="80%" bgcolor="ivory"> +<tr align=center> +<td width="25%"> +<a href="../cref.html">Top</a> +</td><td width="25%"> +<a href="../../C/master_index.html">Master Index</a> +</td><td width="25%"> +<a href="../SYNTAX/keywords.html">Keywords</a> +</td><td width="25%"> +<a href="../../C/FUNCTIONS/funcref.htm">Functions</a> +</td> +</tr> +</table> +</center> +<p> +<hr> +<font color=brown> +<address>Martin Leslie +29-Dec-97</address><p> +</font> +</body> +</html> |