Reflection problem: can not access a member of class java.lang.IllegalAcces

Question

package org.struts.ets.utility;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import org.struts.bean.FieldTrouble;
import org.struts.bean.GenericDAOBean;
public class DynamicObjectCreation
     public static void main(String... args)
          FieldTrouble ft = new FieldTrouble();
          try
               Class<?> c = ft.getClass();
               //Class<?> c = FieldTrouble.class;
               /*Class<?> c = null;
               try
                    c = Class.forName("org.struts.bean.FieldTrouble");
               } catch (ClassNotFoundException e)
                    e.printStackTrace();
               Field f = c.getDeclaredField("var1");
               //f.setInt(ft, 42); // IllegalArgumentException
               f.set(ft, new String("A"));
               System.out.println(ft.getVar1());
               // production code should handle these exceptions more gracefully
          } catch (NoSuchFieldException x)
               x.printStackTrace();
          } catch (IllegalAccessException x)
               x.printStackTrace();
}// If I put FieldTrouble.java in any other package than the current package I am running this code from. I get the following error:
java.lang.IllegalAccessException: Class org.struts.ets.utility.DynamicObjectCreation can not access a member of class org.struts.bean.FieldTrouble with modifiers ""
     at sun.reflect.Reflection.ensureMemberAccess(Unknown Source)
     at java.lang.reflect.Field.doSecurityCheck(Unknown Source)
     at java.lang.reflect.Field.getFieldAccessor(Unknown Source)
     at java.lang.reflect.Field.set(Unknown Source)
     at org.struts.ets.utility.DynamicObjectCreation.main(DynamicObjectCreation.java:35)
I tried all possible ways of creating class as:
Class<?> c = ft.getClass(); OR
Class<?> c = FieldTrouble.class; OR
               /*Class<?> c = null;
               try
                    c = Class.forName("org.struts.bean.FieldTrouble");
               } catch (ClassNotFoundException e)
                    e.printStackTrace();
Edited by: ..-__Kris__-.. on Feb 21, 2008 10:26 AM
Edited by: ..-__Kris__-.. on Feb 21, 2008 10:26 AM

Answer 1

Any hidden performance or memory issue here?
Let us consider an object:
public class SomeObject
     private String fieldA;
     private String fieldB;
     private String fieldC;
     private String fieldD;
     private String fieldE;
     //... say 50 declared fields....
     public SomeObject()
     public SomeObject(String fieldA, String fieldB)
          this.fieldA = fieldA;
          this.fieldB = fieldB;
// getters and setters..     
}When I create an object using the constructor with only two fields initialized such as the following code above, and look at what is happening to other fields as shown in the code below, I see that they are also AVAILABLE, now this is important, but they are set to null. What I wanted to know was, if I created an object with many fields, as many as 50 (getDeclaredFields = 50), and used a constructor with only two input fields to initialize an object, I still have 48 other fields available but set as NULL's. When I create more than 100,000 of these objects in a list and send to a .jsp page, I am unable to understand if this has more memory load than when you use a list of another object which has actually has only two declared fields in it. Each of this new object will have only two declared fields, when I say getDeclaredFields() it would return 2.
This is where I am unable to figure out if this has anything to do with performance or memory, rather, what is the difference between the many possible ways you can initialize an object when there are too many fields which you probably won't use? Either create a new constructor with only two input arguments OR a generic constructor with all fields as input arguments but all those fields which you won't use assigned NULL's OR create another new object with only two declared fields
SomeObject someObj = new SomeObject("abcd","cdef");
          Field[] fields = someObj.getClass().getDeclaredFields();
          System.out.println("Number of available fields: " + fields.length);
          for(int i = 0 ; i < fields.length ; i++)
               try
                    fields.setAccessible(true);
                    System.out.println("Field " + i + ", with value: " + fields[i].get(someObj));
                    fields[i].get(someObj);
               } catch (IllegalArgumentException e)
                    e.printStackTrace();
               } catch (IllegalAccessException e)
                    e.printStackTrace();
          }Edited by: ..-__Kris__-.. on Mar 23, 2008 5:04 PM
Edited by: ..-__Kris__-.. on Mar 23, 2008 5:05 PM