Generic instance maker and class definition in separate files - problem

Question

file: genericinstantiator.java
package testGenericInstantiator;
public final class GenericInstantiator {
     public <T> T makeInstance(Class<T> c) {
          T instance = null;
          try {
               instance = c.newInstance();
          } catch (IllegalAccessException e) {
               // TODO Auto-generated catch block
               e.printStackTrace();
          } catch (InstantiationException e) {
               // TODO Auto-generated catch block
               e.printStackTrace();
          return instance;
file: genericinstantiatorusage.java
package testGenericInstantiator.usage;
import testGenericInstantiator.GenericInstantiator;
final class SillyClass {
     public void sayBoo() {
          System.out.println("boo");
public final class GenericInstantiatorUsage {
     public static void main(String[] args) {
          GenericInstantiator gi = new GenericInstantiator();
          SillyClass sc = gi.makeInstance(SillyClass.class);
          sc.sayBoo();
          System.exit(0);
thrown exception:
java.lang.IllegalAccessException
on the line 'instance = c.newInstance();' in instantiator
reason in jdk:
if the class or its nullary constructor is not accessible.
question:
how to avoid this? (in my situation, the place of making instance and its class MUST be separated in another files)
Edited by: gizmo640 on Mar 27, 2008 11:39 AM

Answer 1

package testGenericInstantiator;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
public final class GenericInstantiator {
     public <T> T makeInstance(Class<T> c) throws IllegalArgumentException, InstantiationException, IllegalAccessException, InvocationTargetException, SecurityException, NoSuchMethodException {
          T instance = null;     
          Class[] emptyParams = {};
          Constructor<T> con = c.getDeclaredConstructor(emptyParams);
          con.setAccessible(true);
          instance = con.newInstance();
          return instance;
}setting constructor to accessible works well too