Dynamic Class loading

[Kathy Thiyagar]

Hi,

I am trying to read a file and create a new instance of the classes whenever it finds the class name from this file and would like to know how to get the Constructor. My code works fine, but when it reaches the Constructor line, it throws ClassNotFoundException. I have all of the required classes compiled in the same folder. Looks like, I am doing something silly here. Can someone point me in the right direction? I am new to this Reflection stuffs.

package test;

import java.util.*;
import java.io.*;
import java.lang.reflect.*;

@SuppressWarnings("unchecked")
public class DynamicLoadingDemo
{
   public static void main(String[] args)
   {
      try
      {
         BufferedReader in = new BufferedReader(new FileReader("E:\\test\\Config.txt"));
         String s;
          while((s = in.readLine())!= null)
          {
               int colon = s.indexOf(':');
               String type = s.substring(0, colon).trim();
               System.out.println(type);
               Integer offset = new Integer(s.substring(colon + 1).trim());
               System.out.println(offset);
               //find and call the right constructor:
               Class eventClass = Class.forName(type);
               System.out.println("EventClass now is: " + eventClass);
               Constructor ctor = eventClass.getConstructor(new Class[] { eventClass, long.class}); // This is where it fails.
               System.out.println("Constructor now is: " + ctor);
          }
      }
      catch(Exception e)
      {
          System.out.println(e);
      }
   }
}

Thanks in advance.

Kathy T.

[Pramod P Deore]

Hello Kathy, Welcome to javaranch

It will be easy if you give code for class which String "type" is stored

 String type = s.substring(0, colon).trim();    

[Kathy Thiyagar]

Hi Pramod,

Thank you for your quick reply. The file that is loading is as follows.

TestClassA : 0
TestClassB : 1

You can create a simple TestClassA and TestClassB and compile them under the test folder. The whole program is really big and for demo, I have only listed partial code here. This code compiles without any issues except this is not getting the Constructor.

Thanks,

Kathy

[Pramod P Deore]

Actually when I created file then the program runs fine.
I think you had not write Constructor properly.

[Pramod P Deore]

when I created file Config.txt and in that I had write "Code:123".

In Code class I had following code

public class Code
{
	public Code(Code c, long l)
	{
		System.out.println ("Inside two arg");
	}
	
	
	public static void main(String[] args)
	{
	}

}

when I run program it print

Inside while
Code
123
EventClass now is: class Code
Constructor now is: public Code(Code,long)

But when I removed the constructor then it will give error as

Inside while
Code
123
EventClass now is: class Code
java.lang.NoSuchMethodException: Code.<init>(Code, long)

So it must not getting the constructor which takes argument as(Code c, long l) .

so check your constructor in that class.

[Kathy Thiyagar]

Thanks Pramode. You are correct. It makes sense. Once again, thank you so much. Take care.

Regards,

Kathy

[Pramod P Deore]

You are most welcome

[Kathy Thiyagar]

Pramode, I have corrected my code and it is working like charm. I have been spending few hours trying to figure out what I am doing wrong here. You are really a Java Guru.

Thanks,

Regards,

Kathy.

[Pramod P Deore]

Here on ranch there are many talented progammer. I am just no one compare to them. It is good to hear that your program run fines.
Best Luck

[Seetharaman Venkatasamy]

@Kathy Thiyagar : *use code tag*, when you post code