How to Find All the Constructors, Fields and Methods of a Class in JAVA

It is possible to use Reflection in Java; Java provides the API in a package named "reflect". Reflection is a feature in thye Java programming language. Reflection allows an executing Java program to "introspect" itself, and manipulate internal properties of the program. For example, it is possible for a Java class that has n number of constructors, methods and fields to be accessed; the details of all the functions (methods) with help of appropriate Class of the reflect package; for example you want to find the constructor of a class then you can use the Constructor class.

Constructor class

Using the Constructor class of the Java reflection API, you can inspect the Constructors of classes and instantiate objects at runtime.

Example

import java.lang.reflect.Constructor;
public class FindConstructor
{
     public static void main(String args[])
     {
          try
          {
              /* Make the Object of Class class and give the fully fath of desired class for finding the constructor  in this example we give the                               java.io.BufferedInputStream class */
              Class c = Class.forName("java.io.BufferedInputStream");
              System.out.println("Constructors:");
              /*by using getConstructor method for get the constructor for Class obj(c)*/
              Constructor constructors[] = c.getConstructors();
              for (int i = 0; i < constructors.length; i++)
              System.out.println(+i+ "-" + constructors[i]);
          }
          catch (Exception e)
          {
             System.out.println("Exception: " + e);
          }
     }
}

0utput

Fields Class

Using the Field class of the Java reflection API you can inspect the Fields of classes and obtain the object's field name, type and the getting and setting fields value.

Example

import java.lang.reflect.Field;
public class MyField
{
public static void main(String args[])
  {
   try
   {

/* Make the Object of Class class and give the fully fath of desired class for finding the constructor  in this example we give the java.lang.reflect.Field class as parameter of forName method */
        Class c = Class.forName("java.lang.reflect.Field");
        System.out.println("Fields:");
         Field fields[] = c.getFields();
        for (int i = 0; i < fields.length; i++)
          System.out.println(+i+"- " + fields[i]);
        }
        catch (Exception e)
        {
             System.out.println("Exception: " + e);
        }
    }
}

Output

Method class

A Method class  providing  information about, and access to, a single method on a class or interface. The reflected method may be a class method or an instance method (including an abstract method).

Example

import java.lang.reflect.Method;
public class MyMethod
{
    public static void main(String args[])
    {
         try
         {

            /* Make the Object of Class class and give the fully fath of desired class for finding the constructor  in this example we give the                   java.lang.reflect.Method class as parameter of forName method */
            Class c = Class.forName("java.lang.reflect.Method");
            System.out.println("methods:");
            Method methods[] = c.getMethods();
            for (int i = 0; i < methods.length; i++)
            System.out.println(+i+"- " + methods[i]);
         }
         catch (Exception e)
         {
              System.out.println("Exception: " + e);
         }
    }
}

Output 

 

Summary

With the help of this example you can access any field, constructor or method of any class and you can get the internal structure of an unknown class so reflection have its importantance.