PrivateFieldHelper Class

Heres a little class I wrote to set private fields. I plan to use it a little for testing, but only when I'm backed into a corner, and can't change code otherwise.

/**
 * 
 * @author Josh Cough
 * 
 */
public class PrivateFieldHelperImpl implements PrivateFieldHelper {

 Class clazz;

 /**
  * 
  * @param c
  */
 public PrivateFieldHelperImpl(Class c) { this.clazz = c; }

 /*
  * (non-Javadoc)
  * @see com.joshcough.reflect.PrivateFieldHelper#setStaticFieldValue(java.lang.String, java.lang.Object)
  */
 public void setStaticFieldValue(String fieldName, Object newValue)
   throws IllegalArgumentException, NoSuchFieldException {
  setPrivateFieldValue(findPrivateStaticField(fieldName), null, newValue);
 }

 /*
  * (non-Javadoc)
  * @see com.joshcough.reflect.PrivateFieldHelper#getStaticFieldValue(java.lang.String)
  */
 public Object getStaticFieldValue(String fieldName) 
  throws NoSuchFieldException, IllegalArgumentException  {
  return getPrivateFieldValue(null, findPrivateStaticField(fieldName));
 }

 /*
  * (non-Javadoc)
  * @see com.joshcough.reflect.PrivateFieldHelper#getInstanceFieldValue(java.lang.Object, java.lang.String)
  */
 public Object getInstanceFieldValue(Object instance, String fieldName) 
  throws NoSuchFieldException, IllegalArgumentException  {
  return getPrivateFieldValue(instance, findPrivateInstanceField(fieldName));
 }
 
 /*
  * (non-Javadoc)
  * @see com.joshcough.reflect.PrivateFieldHelper#setInstanceFieldValue(java.lang.Object, java.lang.String, java.lang.Object)
  */
 public void setInstanceFieldValue(Object instance, String fieldName, Object newValue)
   throws IllegalArgumentException, NoSuchFieldException {
  setPrivateFieldValue(findPrivateInstanceField(fieldName), instance, newValue);
 }
 
 /**
  * 
  * @param f
  * @return
  * @throws 
  */
 private Object getPrivateFieldValue(Object instance, Field f) {
  f.setAccessible(true);
  Object o;
  try {
   o = f.get(instance);
  }  catch (IllegalAccessException e) {
   throw new PrivateFieldException(e);
  }
  f.setAccessible(false);
  return o;
 }

 /**
  * 
  * @param f
  * @param newValue
  * @throws 
  */
 private void setPrivateFieldValue(Field f, Object instance, Object newValue){
  f.setAccessible(true);
  try {
   f.set(instance, newValue);
  } catch (IllegalAccessException e) {
   throw new PrivateFieldException(e);
  }
  f.setAccessible(false);
 }

 /**
  * 
  * @param fieldName
  * @return
  * @throws NoSuchFieldException
  */
 private Field findPrivateStaticField(String fieldName) throws NoSuchFieldException {
  for (Field f : clazz.getDeclaredFields()) {
   if (f.getName().equals(fieldName)) {
    if (Modifier.isStatic(f.getModifiers()))
     return f;
   }
  }
  throw new NoSuchFieldException();
 }

 /**
  * 
  * @param fieldName
  * @return
  * @throws NoSuchFieldException
  */
 private Field findPrivateInstanceField(String fieldName) throws NoSuchFieldException {
  for (Field f : clazz.getDeclaredFields()) {
   if (f.getName().equals(fieldName)) {
    if (! Modifier.isStatic(f.getModifiers()))
     return f;
   }
  }
  throw new NoSuchFieldException();
 }
 
}