新手上路，請多指教。
關於面向對象編程，我的理解
1)封裝具有共性的事物屬性和行為
2)接口和實現的分離
如果有一句話來說的話，那就是“用一個類去實例化各種各樣的對象”。
下面是我在酷殼所看到的一篇文章《如何理解面向對象編程》。
關於裡面的三段代碼。
這是最初的版本。
public class PrintOS
{
public static void main(final String[] args)
{
String osName = System.getProperty("os.name") ;
if (osName.equals("SunOS") || osName.equals("Linux"))
{
System.out.println("This is a UNIX box and therefore good.") ;
}
else if (osName.equals("Windows NT") || osName.equals("Windows 95"))
{
System.out.println("This is a Windows box and therefore bad.") ;
}
else
{
System.out.println("This is not a box.") ;
}
}
}接著就是過程化的版本。
public class PrintOS
{
private static String unixBox()
{
return "This is a UNIX box and therefore good." ;
}
private static String windowsBox()
{
return "This is a Windows box and therefore bad." ;
}
private static String defaultBox()
{
return "This is not a box." ;
}
private static String getTheString(final String osName)
{
if (osName.equals("SunOS") || osName.equals("Linux"))
{
return unixBox() ;
}
else if (osName.equals("Windows NT") ||osName.equals("Windows 95"))
{
return windowsBox() ;
}
else
{
return defaultBox() ;
}
}
public static void main(final String[] args)
{
System.out.println(getTheString(System.getProperty("os.name"))) ;
}
}接下來是幼稚的面向對象編程
PrintOS.java
public class PrintOS
{
public static void main(final String[] args)
{
System.out.println(OSDiscriminator.getBoxSpecifier().getStatement()) ;
}
}OSDiscriminator.java
public class OSDiscriminator // Factory Pattern
{
private static BoxSpecifier theBoxSpecifier = null ;
public static BoxSpecifier getBoxSpecifier()
{
if (theBoxSpecifier == null)
{
String osName = System.getProperty("os.name") ;
if (osName.equals("SunOS") || osName.equals("Linux"))
{
theBoxSpecifier = new UNIXBox() ;
}
else if (osName.equals("Windows NT") || osName.equals("Windows 95"))
{
theBoxSpecifier = new WindowsBox() ;
}
else
{
theBoxSpecifier = new DefaultBox () ;
}
}
return theBoxSpecifier ;
}
}BoxSpecifier.java
public interface BoxSpecifier
{
String getStatement() ;
}DefaultBox.java
public class DefaultBox implements BoxSpecifier
{
public String getStatement()
{
return "This is not a box." ;
}
}UNIXBox.java
public class UNIXBox implements BoxSpecifier
{
public String getStatement()
{
return "This is a UNIX box and therefore good." ;
}
}WindowsBox.java
public class WindowsBox implements BoxSpecifier
{
public String getStatement()
{
return "This is a Windows box and therefore bad." ;
}
}OO大師的方案
PrintOS.java
public class PrintOS
{
public static void main(final String[] args)
{
System.out.println(OSDiscriminator.getBoxSpecifier().getStatement()) ;
}
}OSDiscriminator.java
public class OSDiscriminator // Factory Pattern
{
private static java.util.HashMap storage = new java.util.HashMap() ;
public static BoxSpecifier getBoxSpecifier()
{
BoxSpecifier value = (BoxSpecifier)storage.get(System.getProperty("os.name")) ;
if (value == null)
return DefaultBox.value ;
return value ;
}
public static void register(final String key, final BoxSpecifier value)
{
storage.put(key, value) ; // Should guard against null keys, actually.
}
static
{
WindowsBox.register() ;
UNIXBox.register() ;
MacBox.register() ;
}
}BoxSpecifier.java
public interface BoxSpecifier
{
String getStatement() ;
}DefaultBox.java
public class DefaultBox implements BoxSpecifier // Singleton Pattern
{
public static final DefaultBox value = new DefaultBox () ;
private DefaultBox() { }
public String getStatement()
{
return "This is not a box." ;
}
}UNIXBox.java
public class UNIXBox implements BoxSpecifier // Singleton Pattern
{
public static final UNIXBox value = new UNIXBox() ;
private UNIXBox() { }
public String getStatement()
{
return "This is a UNIX box and therefore good." ;
}
public static final void register()
{
OSDiscriminator.register("SunOS", value) ;
OSDiscriminator.register("Linux", value) ;
}
}WindowsBox.java
public class WindowsBox implements BoxSpecifier // Singleton Pattern
{
public static final WindowsBox value = new WindowsBox() ;
private WindowsBox() { }
public String getStatement()
{
return "This is a Windows box and therefore bad." ;
}
public static final void register()
{
OSDiscriminator.register("Windows NT", value) ;
OSDiscriminator.register("Windows 95", value) ;
}
}MacBox.java
public class MacBox implements BoxSpecifier // Singleton Pattern
{
public static final MacBox value = new MacBox() ;
private MacBox() { }
public String getStatement()
{
return "This is a Macintosh box and therefore far superior." ;
}
public static final void register()
{
OSDiscriminator.register("Mac OS", value) ;
}
}上面幾個版本的代碼，給我的感覺是越來越來難看懂，本來用if-else語句或者switch語句就可以簡單明了的實現所需要的功能。面向對象編程是為了方便我們，使得我們的開發更加的高效率。可是，上面的面向對象反而使得有點畫蛇添足。應該合理的運用面向對象編程，而不是濫用。
本文出自 “淡定的dreamer” 博客，請務必保留此出處http://idiotxl1020.blog.51cto.com/6419277/1288523
