Login | Register   
RSS Feed
Download our iPhone app
Browse DevX
Sign up for e-mail newsletters from DevX

By submitting your information, you agree that devx.com may send you DevX offers via email, phone and text message, as well as email offers about other products and services that DevX believes may be of interest to you. DevX will process your information in accordance with the Quinstreet Privacy Policy.


Charting Unknown Waters in JDK 1.4

Java Specialist Dr. Heinz Kabutz has been digging through the classes in the java.util.* package of the JDK 1.4. This article highlights some of the gems he discovered right away.




Building the Right Environment to Support AI, Machine Learning and Deep Learning

ondering what I would dig up in the JDK 1.4 source code, I recently started looking through the classes in the java.util.* package—without even the subpackages. That alone kept me busy for most of an afternoon, and although I have not finished exploring that J2SE release yet, I already have enough material for several articles. The following are some of the gems I discovered right away.

Did You Know toString() was Broken for Collections?
In the collection classes, all hell breaks loose when you try to call toString() on a collection that contains itself. For example, consider the following code:

import java.util.Hashtable; public class HashtableTest { public static void main(String[] args) { Hashtable ht = new Hashtable(); ht.put("Heinz", "Kabutz"); ht.put(ht, "all"); ht.put("all", ht); ht.put(ht, ht); try { System.out.println(ht); } catch (StackOverflowError e) { System.out.println("Caused Stack Overflow Error!"); } } }

Running this program under JDK 1.3 or older versions generates a stack overflow. In JDK 1.4, however, the output is:

{Heinz=Kabutz, all=(this Map), (this Map)=all, (this Map)=(this Map)}

This same principle applies to the other collections in JDK 1.4.

Is it a good idea to use a Hashtable as a key, you might ask. Dont forget what happens when the hash code of a key changes during its life (see Issue 031 of The Java(tm) Specialists' Newsletter). Each time a Hashtable changes, its hash code changes as well. So you should not use it as a key. The question I have is why—despite the seemingly limitless amount of stupid code written every day—the people at Sun didn't anticipate programmers adding a collection to itself.

Comment and Contribute






(Maximum characters: 1200). You have 1200 characters left.



Thanks for your registration, follow us on our social networks to keep up-to-date