Getting a Class Descriptor
Problem
You want to get a Class
object from a class name
or instance.
Solution
If the class name is known at compile time, you can get the class
instance using the compiler keyword
.class
, which works on
any object. However, the Object
class does not
have class
as a field, so this strikes some
observers as a bit of a hack. Nonetheless, it works. Use it.
Otherwise, if you have an object (an instance of a class), you can
call the java.lang.Object
method
getClass( )
, which
returns the
Class
object for the object’s
class (now that was a mouthful!):
import java.util.*; /** * Show the Class keyword and getClass( ) method in action. */ public class ClassKeyword { public static void main(String[] argv) { System.out.println("Trying the ClassName.class keyword:"); System.out.println("Object class: " + Object.class); System.out.println("String class: " + String.class); System.out.println("Calendar class: " + Calendar.class); System.out.println("Current class: " + ClassKeyword.class); System.out.println( ); System.out.println("Trying the instance.getClass( ) method:"); System.out.println("Robin the Fearless".getClass( )); System.out.println(Calendar.getInstance().getClass( )); } }
When we run it, we see:
C:\javasrc\reflect>java ClassKeyword Trying the ClassName.class keyword: Object class: class java.lang.Object String class: class java.lang.String Calendar class: class java.util.Calendar Current class: class ClassKeyword Trying the instance.getClass( ) method: class ...
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