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Computing Thoughts
Generics and Packages
by Bruce Eckel
November 10, 2005
There appear to be some strange side effects on packages when using generics.


Consider the following file:

package code;

interface HasColor {
  java.awt.Color getColor();

class Dimension {
  int x, y, z;

class ColoredDimension<T extends Dimension & HasColor> {
  T item;
  ColoredDimension(T item) { this.item = item; }
  T getItem() { return item; }
  java.awt.Color f() { return item.getColor(); }
  int getX() { return item.x; }

When you run the compiler, you get the following error message: x is not public in code.Dimension; cannot be accessed from outside package
  int getX() { return item.x; }
1 error

Since all the code is in the same package, this is probably a bug. But with generics, it's always hard to tell.

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About the Blogger

Bruce Eckel ( provides development assistance in Python with user interfaces in Flex. He is the author of Thinking in Java (Prentice-Hall, 1998, 2nd Edition, 2000, 3rd Edition, 2003, 4th Edition, 2005), the Hands-On Java Seminar CD ROM (available on the Web site), Thinking in C++ (PH 1995; 2nd edition 2000, Volume 2 with Chuck Allison, 2003), C++ Inside & Out (Osborne/McGraw-Hill 1993), among others. He's given hundreds of presentations throughout the world, published over 150 articles in numerous magazines, was a founding member of the ANSI/ISO C++ committee and speaks regularly at conferences.

This weblog entry is Copyright © 2005 Bruce Eckel. All rights reserved.

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