[LANG-20] Infinite loop in ToStringBuilder.reflectionToString for inner classes

• Type: Bug
• Status: Closed
• Priority: Blocker
• Resolution: Fixed
• Affects Version/s: 2.0
• Fix Version/s: 2.0

Environment

Operating System: All
Platform: PC

• Bugzilla Id: 15986
• Assignee: Unassigned
• Reporter: Per Velschow
• Created: 11/Jan/03 13:27
• Updated: 16/May/06 12:44
• Resolved: 16/May/06 12:44

Description

ToStringBuilder.reflectionToString() enters an infinite loop when used with the
following example:

/////////////////////////////
public class Outer {
Inner inner = new Inner();
class Inner {
public String toString()

{ return ToStringBuilder.reflectionToString(this); }

}
public String toString()

{ return ToStringBuilder.reflectionToString(this); }

public static void main(String[] args)

{ Outer outer = new Outer(); System.out.println(outer); }

}
/////////////////////////////

The reason is that the two classes refer to each other via the explicit field
inner and the implicit field Outer.this.

The bug can be resolved by skipping the implicit fields. Is there any good
reason for printing those anyway?

I am not sure what is the best way to detect if a field is an implicit field.
But I patched the code myself in a way that seemed to work:

/////////////////////////////
public static String reflectionToString(Object object, ToStringStyle style,
boolean outputTransients) {
if (object == null)

{ throw new IllegalArgumentException("The object must not be null"); }

if (style == null)

{ style = getDefaultStyle(); }

Field[] fields = object.getClass().getDeclaredFields();
Field.setAccessible(fields, true);
ToStringBuilder builder = new ToStringBuilder(object, style);
for (int i = 0; i < fields.length; ++i) {
Field f = fields[i];
if (!f.getName().startsWith("this$")) {
if (outputTransients || !Modifier.isTransient(f.getModifiers())) {
if (!Modifier.isStatic(f.getModifiers())) {
try

{ builder.append(f.getName(), f.get(object)); }

catch (IllegalAccessException ex)

{ //this can't happen. Would get a Security exception instead //throw a runtime exception in case the impossible happens. throw new InternalError("Unexpected IllegalAccessException"); }

}
}
}
}
return builder.toString();
}
/////////////////////////////

Notice the extra if statement that tests for field names starting with "this$".
I don't know if this is guaranteed to work always, though.