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reflection api

Posted on 2011-09-05
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Last Modified: 2012-05-12
I would like to know about reflection api. When we use it. What are the uses of it. How to use it. Thanks in advance
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Question by:gudii9
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for_yan earned 500 total points
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this is simple explanation:
http://java.sun.com/developer/technicalArticles/ALT/Reflection/


Reflection is a feature in the Java programming language. It allows an executing Java program to examine or "introspect" upon itself, and manipulate internal properties of the program. For example, it's possible for a Java class to obtain the names of all its members and display them.

The ability to examine and manipulate a Java class from within itself may not sound like very much, but in other programming languages this feature simply doesn't exist. For example, there is no way in a Pascal, C, or C++ program to obtain information about the functions defined within that program.

One tangible use of reflection is in JavaBeans, where software components can be manipulated visually via a builder tool. The tool uses reflection to obtain the properties of Java components (classes) as they are dynamically loaded.
A Simple Example

To see how reflection works, consider this simple example:
   import java.lang.reflect.*;
 
   public class DumpMethods {
      public static void main(String args[])
      {
         try {
            Class c = Class.forName(args[0]);
            Method m[] = c.getDeclaredMethods();
            for (int i = 0; i < m.length; i++)
            System.out.println(m[i].toString());
         }
         catch (Throwable e) {
            System.err.println(e);
         }
      }
   }


For an invocation of:

  java DumpMethods java.util.Stack

the output is:

  public java.lang.Object java.util.Stack.push(
    java.lang.Object)
   public synchronized 
     java.lang.Object java.util.Stack.pop()
   public synchronized
      java.lang.Object java.util.Stack.peek()
   public boolean java.util.Stack.empty()
   public synchronized 
     int java.util.Stack.search(java.lang.Object)

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That is, the method names of class java.util.Stack are listed, along with their fully qualified parameter and return types.

This program loads the specified class using class.forName, and then calls getDeclaredMethods to retrieve the list of methods defined in the class. java.lang.reflect.Method is a class representing a single class method.
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