Metaclasses - Revision history

Suhridk at 12:51, 7 January 2012

2012-01-07T12:51:38Z

Suhridk at 12:38, 7 January 2012

2012-01-07T12:38:34Z

Suhridk at 14:54, 17 December 2011

2011-12-17T14:54:48Z

Suhridk at 14:49, 17 December 2011

2011-12-17T14:49:35Z

Suhridk: Created page with "* Each object belongs to a class. * But, Everything is an object. * So, classes are '''objects''' apart from being classes. String s = "Hello"; C..."

2011-12-17T14:48:22Z

Created page with "* Each object belongs to a class. * But, Everything is an object. * So, classes are '''objects''' apart from being classes. <syntaxhighlight lang="java5"> String s = "Hello"; C..."

New page

* Each object belongs to a class.
* But, Everything is an object.
* So, classes are '''objects''' apart from being classes.

<syntaxhighlight lang="java5">
String s = "Hello";
Class stringClassObj = s.getClass();
</syntaxhighlight>

* So the class object (stringClassObj) is an instance of which class ?
* It is an instance of java.lang.Class.
* java.lang.Class extends java.lang.Object since classes are objects.
* So java.lang.Class is a metaclass. Instances of java.lang.Class are classes.
* A class defines the behaviour of its instances. Similarly, a metaclass defines the behavior of the classes that are its instances.
* E.g. java.lang.Class has methods that defined the behavior of its instances.
** e.g. getName(), getDeclaredFields(), getMethods(),

* e.g. getMethods return objects which are of type Method class. Instances of java.lang.reflect.Method are methods.
* The method class defines behavior of all methods, for e.g. getReturnType(), getModifiers() etc.

[[Category:OODE]]

@@ Line 20: / Line 20: @@
 * java.lang.Class is not a complete class, since it is declared as final. We cannot add behavior to it or specialize it.
 * This whole meta thing is '''reflection''' - a program can reflect on itself.
 * Useful for tools. e.g. Eclipse. Automatic method drop down possibly reflects on the Class object and gets all its declared methods.
 [[Category:OODE]]

@@ Line 12: / Line 12: @@
 * java.lang.Class extends java.lang.Object since classes are objects.
 * So java.lang.Class is a metaclass. Instances of java.lang.Class are classes.
-* A class defines the behaviour of its instances. Similarly, a metaclass defines the behavior of the classes that are its instances.
+* A class defines the behaviour of its instances. Similarly, '''a metaclass defines the behavior of the classes that are its instances.'''
 * E.g. java.lang.Class has methods that defined the behavior of its instances.
 ** e.g. getName(), getDeclaredFields(), getMethods(),

@@ Line 17: / Line 17: @@
 * e.g. getMethods return objects which are of type Method class. Instances of java.lang.reflect.Method are methods.
-* The method class defines behavior of all methods, for e.g. getReturnType(), getModifiers() etc.
+* The method class defines behavior of all methods, so it is a meta-method. for e.g. getReturnType(), getModifiers() etc.
 * java.lang.Class is not a complete class, since it is declared as final. We cannot add behavior to it or specialize it.
 [[Category:OODE]]