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class, and several constructors of other classes that constitute upper 
inheritance hierarchyes. This class inherits from these classes using extends.
 
cDPI and threadDeEstaClase are general static variables (not local to "abrir"). 
Method probarEstaClase() is a non-static initialization method that is fired 
before the thread is started.

When I run this program, first  ConfiguracionProcesadorDeImagenes is started 
invoking its "abrir" method, and everything goes fine.

But when ConfiguracionProcesadorDeImagenes exits its run method and 
LaIniciacion class is started (when its "abrir" method is invoked using 
reflection) I get a InvocationTargetException. Both getTargetException() and 
printStackTrace() show that there has been a NullPointerException thrown by 
"abrir" this time.

Why does "abrir" throw a NullPointer Exception?
How can this be avoided?

Note: "abrir" must be static or no satisfactory behavior of the program is 
obtained.

Thanks a lot in advance,

JG.-



Here is the code of two classes that are also threads and perform the reflection 
procedure (I have already included this code in a previous message):

//AdministradorDeReflexion.java

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

/**
@version 2.0
@author Jose Gengler
@author jgengler at iname.com
*/
public class AdministradorDeReflexion extends Thread
implements Observer
{

	public String stringClaseAnterior = new String("1");
	public String stringClaseActual = new String("2");
	public String stringClaseSiguiente = new String("3");
	private boolean booleanPrimerUso = true;
	static int count;
	ActivadorDeClases activadorDeLaClaseActual;
	boolean booleanCerrandoElProcesadorActual = false;
	
	
	
	public AdministradorDeReflexion()
	{
	}

	void iniciarNuevoProcesador(String stringNuevaClase1)
	{
		System.gc();
		System.out.println("          " + stringClaseActual);
		System.out.println("          " + stringClaseSiguiente);
		stringClaseActual = stringNuevaClase1;
		stringClaseSiguiente = stringClaseActual;
		
		activadorDeLaClaseActual = null;
		activadorDeLaClaseActual  = new ActivadorDeClases(stringClaseActual);
		activadorDeLaClaseActual.start();

		while(stringClaseActual.equals(stringClaseSiguiente))
		{
			//count++;
			//System.out.println("                    " + count + "   " + booleanCerrandoElProcesadorActual);

			
			booleanCerrandoElProcesadorActual = 
			((Boolean)(activadorDeLaClaseActual.averiguarElValorDeUnaVariable("booleanCerrandoEstaClase"))).booleanValue();

			//System.out.println("" + booleanCerrandoElProcesadorActual);

			if(booleanCerrandoElProcesadorActual)
			{
				stringClaseActual = (String)(activadorDeLaClaseActual.averiguarElValorDeUnaVariable("stringClaseActual"));
				stringClaseAnterior = (String)(activadorDeLaClaseActual.averiguarElValorDeUnaVariable("stringClaseAnterior"));
				stringClaseSiguiente = (String)(activadorDeLaClaseActual.averiguarElValorDeUnaVariable("stringClaseFutura"));


				activadorDeLaClaseActual.cerrarActivadorDeClases();
			}
		}	

	
		
	}  

	public void update(Observable Procesador1, Object arg)
	{
	}
	public void run()
	{
		while(true)
		{

			
			if(booleanPrimerUso) 
			{
				iniciarNuevoProcesador("LaIniciacion");
				booleanPrimerUso = false;
			}				
			else 
if(!(stringClaseActual.equals(stringClaseSiguiente)))
			{
				iniciarNuevoProcesador(stringClaseSiguiente);
			}

		
			
		
		}
	}
	public static void main(String[] args)
	{
		AdministradorDeReflexion aDR = new 
AdministradorDeReflexion();
		aDR.start();
	}
}


********************

//ActivadorDeClases.java

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

/**
@version 2.0
@author Jose Gengler
@author jgengler at iname.com
*/
public class ActivadorDeClases 
extends Thread
// implements Observer
{
	String stringNombreDeLaClase = new String();
	public Class newClass;
	int count;
	boolean booleanCerrarActivadorDeClases = false;
	boolean booleanIniciandoUnaNuevaClase = true;
	



	public ActivadorDeClases(String stringNombreDeLaClase1)
	{
		stringNombreDeLaClase = stringNombreDeLaClase1;
		try
		{
			newClass = Class.forName(stringNombreDeLaClase);
		}	catch(ClassNotFoundException e) {System.out.println(e);}
	}

	public  void invocarUnMetodo(String stringNombreDelMetodo1)
	{
		try
		{
			Method theMethod;
			Class[] parameterTypes;
								
			parameterTypes = new Class[0];
			theMethod = newClass.getMethod(stringNombreDelMetodo1, parameterTypes);
			
			System.gc();
			System.out.println("" + theMethod);
			theMethod.invoke(null, new Object[0]);

						
		}	catch(NoSuchMethodException e) {System.out.println(e);}
			catch(IllegalAccessException e) {System.out.println(e);}
			catch(InvocationTargetException e) {	System.out.println(e);
								System.out.println(e.getTargetException());
								e.printStackTrace();
							}
		
	}

	public Object averiguarElValorDeUnaVariable(String stringNombreDeLaVariable1)
	{
		Object o = new Object();
		Field fieldParaAveriguarValoresDeVariables;
		try 				{
                  		fieldParaAveriguarValoresDeVariables = newClass.getField(stringNombreDeLaVariable1);


				o = fieldParaAveriguarValoresDeVariables.get(o);
								
			}	catch (NoSuchFieldException e) {System.out.println(e); } 
				catch (SecurityException e) {System.out.println(e); }
				catch (IllegalAccessException e) {System.out.println(e); }
		return(o);
	}

	public void cerrarEstaClase()
	{
		Object o = new Object();
		Field fieldParaAveriguarValoresDeVariables;
		
		try
		{
			fieldParaAveriguarValoresDeVariables = newClass.getField("booleanCerrandoEstaClase");
			boolean booleanFalso = false;
			Boolean objetoBoolean = new Boolean(booleanFalso);
			fieldParaAveriguarValoresDeVariables.set(o, objetoBoolean);

		}	catch (NoSuchFieldException e) {System.out.println(e); } 
			catch (SecurityException e) {System.out.println(e); }
			catch (IllegalAccessException e) {System.out.println(e); }
				
	}

	public void run()
	{
		while(true)
		{
			//count++;
			//System.out.println("                                                 " + count);
			
			if(booleanIniciandoUnaNuevaClase)
			{
				System.out.println("" + booleanIniciandoUnaNuevaClase);
				invocarUnMetodo("abrir");
				booleanIniciandoUnaNuevaClase = false;
			}
			if(booleanCerrarActivadorDeClases)
			{
				cerrarEstaClase();
				return;
			}
		}
	}

	public void cerrarActivadorDeClases()
	{
		booleanCerrarActivadorDeClases = true;
	}
}


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