I have a TestCase as follows...

package example;

import java.util.Date;

import junit.framework.TestCase;

public class JavaBeanTest extends TestCase {

public JavaBeanTest(String testName) {
 super(testName);
}

public void testThrowawayCopy() throws Exception {
 // setup
 final JavaBean bean = new JavaBean();
 bean.setId(1L);
 bean.setName("hello");
 // exercise
 final JavaBean copy = bean.throwawayCopy();
 bean.setExpired(new Date());
 copy.setId(2L);
 copy.setName("world");
 // verify
 assertEquals("id affected by copy.setId(long) call", 2L, bean.getId());
 assertEquals("name not affected by copy.setName(String) call", "hello",
bean.getName());
 assertNotNull("expired has changed", bean.getExpired());

 assertEquals("id has changed", 2L, copy.getId());
 assertEquals("name has changed", "world", copy.getName());
 assertNull("expired not affected by bean.setExpired(Date) call",
copy.getExpired());
}

public static Test suite() {
 TestSuite suite = new TestSuite();
 Test test = new JavaBeanTest("testThrowawayCopy");
 for (int i = 0; i < 1000; i++) {
  suite.addTest(test);
 }
 return suite;
}

}

...for which I have a JavaBean class as follows...

package example;

import java.lang.reflect.Method;
import java.util.Date;

public class JavaBean {

private long id;
private String name;
private Date expired;

public JavaBean() {
 // default constructor for JavaBean
}

public Date getExpired() {
 return expired;
}

public void setExpired(Date expired) {
 this.expired = expired;
}

public long getId() {
 return id;
}

public void setId(long id) {
 this.id = id;
}

public String getName() {
 return name;
}

public void setName(String name) {
 this.name = name;
}

public JavaBean throwawayCopy() {
 return new ThrowawayJavaBean();
}

private final class ThrowawayJavaBean extends JavaBean {

 private boolean propagateId;

 private ThrowawayJavaBean() {
  copyProperties();
  propagateId = true;
 }

 private void copyProperties() {
  try {
   Method[] methods = JavaBean.this.getClass().getDeclaredMethods();
   for (int i = 0; i < methods.length; i++) {
    final Method source = methods[i];
    if (source.getName().startsWith("get")) {
     Method target = getClass().getMethod("set" +
source.getName().substring(3), new Class[] { source.getReturnType() });
     target.invoke(this, new Object[] { source.invoke(JavaBean.this, new
Object[] {}) });
    }
   }
  } catch (Exception e) {
   throw unchecked(e);
  }
 }

 public void setId(long id) {
  super.setId(id);

  if (propagateId) {
   JavaBean.this.setId(id);
  }
 }

 private RuntimeException unchecked(Exception e) {
  if (e instanceof RuntimeException) {
   return (RuntimeException) e;
  }
  return new RuntimeException(e);
 }

}

}

This code has been adapted from some code in a production application at my
work.  The production code actually uses Spring's
BeanUtils.copyProperties(Object source, Object target) method in the
ThrowawayJavaBean constructor, but we should be accomplishing the same thing
by using reflection directly.

As you can see, the ThrowawayJavaBean class is a *private* nested class.
During load tests of the production application, the production code
(running in Tomcat) *sometimes* experiences an IllegalAccessException due to
the fact that we're using reflection against a private nested class.  The
problem has never occurred when the visibility of the nested class is
public.  Additionally, I have *never* seen the exception occur in the JUnit
TestRunner with neither the code I have presented above, nor the production
code itself.

My confusion lies with the question of why the IllegalAccessException occurs
only infrequently in the production code running under Tomcat instead of
always occurring.  That is, why doesn't (wouldn't) it happen all the
time--for example, in my TestCase?

Thanks for your time.