Found Fishbowl through my Google Relevance link today and found well expressed shared neurons.

11:37:06 AM    

Careful considered subclassing combined with helpfull overloading can easily lead to this:

java.lang.StackOverflowError 
 at java.lang.String.<init>(String.java:422) 
 at java.lang.StringBuffer.toString(StringBuffer.java:1225) 
 at test.TestSub.act(Main.java:23) 
 at test.TestBase.act(Main.java:36) 
 at test.TestSub.act(Main.java:27)
 at test.TestSub.act(Main.java:23) 
 at test.TestBase.act(Main.java:36)
....

Code snippet to play this game at home:

 8 package test;
 9
14 public class Main {
15
16 public static void main(String[] args) {
17 (new TestSub()).act(5);
18 }
19 }
20
21 class TestSub extends TestBase{
22 public void act(int i) {
23 act(""+i); //changing this to super.act(i) solves the problem!
24 }
25
26 public void act(String s) {
27 super.act(s);
28 }
29 }
30
31 class TestBase {
32 public void act(int i){
33 System.out.println(i);
34 }
35 public void act(String s){
36 act(Integer.parseInt(s));
37 }
38 }

Lesson to learn:

• If you have overloaded methods in a class that is to be subclassed (not final) then you should make sure that the javadoc going with it clearly states how the internal overloading is done.
• If you are overriding methods, always check the baseclass javadoc for overloaded side-effects like this. And delegate to super instead of to an overloaded version on the same level.

By the way I got to learn this the hard way making my own XMLFilter with overriden: XMLFilterImpl.parse(String SystemId) AND XMLFilterImpl.parse(InputSource input).
The resolution is snap, the insight is immediate, the bite was nevertheless unexpected.

11:21:42 AM