Reflection API

Reflection API : A Brief Introduction:-

      "Reflection API is a powerful technique (that provides the facility) to find-out its environment as well as to inspect the class itself. Reflection API was included in Java 1.1."

  

      The classes of Reflection API are the part of the package java.lang.reflect and the methods of Reflection API are the parts of the package java.lang.class. It allows the user to get the complete information about interfaces, classes, constructors, fields and  various methods being used. It also provides an easy way to create a Java Application that was not possible before Java 1.1. You can create methods like event handlers, hash code etc and also find-out the objects and classes.

     
     With the help of Reflection API you can get the information about any class of the java.lang package. There are some useful methods like getName() and getInterfaces(), which allows us to retrieve the name of the class and the interfaces of the package respectively.

1.  Getting the implemented Interfaces:-  

         In this section you will learn how to retrieve an Interface (that included in the program) by using the getInterfaces() method. Here is an example that provides the usage of the getInterfaces() method in more detail.

         Create an object of class Finterface and assign it with java.util.Integer.class.. Now retrieve Interfaces (included in the program) and store their references in an array of class Class by using the getInterfaces() method.

  

Here is the code of the Example :
Finterface.java:

import java.lang.reflect.*; public class Finterface {   public static void main(String str[]){   Class cls = java.util.List.class;   Class[] intfs = cls.getInterfaces();   int len = intfs.length;   for (int i =0; i < len; i++)   {   System.out.println(intfs[i]);   }   } }

Here is the output of this Example :

 interface java.util.Collection 

Retrieving the class name through Reflection API:-  

     

        A more generic way, how to retrieve the name of the class (that is used in the program) that reflects the package name by using the getName() method. Here is an example that provides the proper way to use the getName() method.
      Here we create an object of class Fclass and assign the reference of the class java.util.Integer.class to it. Now retrieve the class name (that is included in the program) by using the getName() method.

 

Here is the code of the Example :



Fclass.java-

import java.lang.reflect.*; public class Fclass{   public static void main(String[] args){   Class cls = java.lang.Integer.class;   String info;   info = cls.getName(); // It will show java.lang.Integer   System.out.println(info);   } }

Here is the output of the Example :
   java.lang.Integer  

Finding out the super class name of the class:-

 

   

   Here we show you the way to find out the Superclass name by using the getSuperclass() method. The given example demonstrates the use of getSuperclass() method in more detail.

     Create a class "Fsupercls". Populate it with the Checkbox objects. Now retrieve the Superclass name by using the getSuperclass() method.

Here is the code of the Example :

Fsupercls.java: 

import java.lang.reflect.*; import java.awt.*; public class Fsupercls  {  public static void main(String[] args) {  Checkbox big = new Checkbox();  printName(big);  }  static void printName(Object objct) {  Class cls = objct.getClass();  Class sup = cls.getSuperclass();   System.out.println(sup);  } }

Here is the output of the Example :
class java.awt.Component

Getting the method name used in the Application:- 

    In this section we describe how to retrieve method name by using the getMethods() method. Here is an example that demonstrates the use of the getMethods() method in more detail.

     Define a class named "Fmethod" and then create an object of this class and get the reference of java.util.Integer.class into it. Now retrieve the method name by using the getMethods() method.

Here is the code of the Example :

Fmethod.java:

import java.lang.reflect.*; public class Fmethod{   public static void main(String[] args){   Class cls = java.lang.Integer.class;   Method method = cls.getMethods()[0];   String info;   info = method.getName();    System.out.println(info);   } }

Here is the output of the Example :


hashCode