The methods java.lang.Class.getResourceAsStream and java.lang.ClassLoader.getResourceAsStream returns null if an exclamation mark is part of the working dir.
In other words:
Reading from a jar which is stored in a directory which contains an exclamation mark will throw a NullPointerException.

If you read a text file from a jar usually you use the instruction
Inputstream is = getClass().getResourceAsStream("a_file_in_jar");

Usually the method getResourceAsStream returns an Object of class InputStream if the file exists in the jar. But, if you store the jar file in a directory which directoryname contains an exclamation mark, e. g. "!oops" or "bug!" or "Go!Zilla" the method getResourceAsStream will return null instead of an InputStream object. This will cause a NullPointerException if you want to read from the file.

I've found this bug in 1.3.1_04, 1.4.0_01 and 1.4.1 beta in both Solaris and Windows JRE distributions.

Testcase:
---------
1. Make a directory where an exclamation mark is part of the directoryname
and change into that directory
(use ksh and "back slash, exclamation mark") to avoid shell-interpretation)
% ksh
$ mkdir Go\!Zilla
$ cd Go\!Zilla

2. Create source ReadFromJar.java

$ cat ReadFromJar.java
import java.io.*;

public class ReadFromJar {

  public static void main(String[] args) {
    new ReadFromJar();
  }
 
  public ReadFromJar() {
     readTextFromJar("ReadFromJar.java");
  }
 
  public void readTextFromJar(String s) {
    String thisLine;
    try {
      InputStream is = getClass().getResourceAsStream(s);
      // returns null if a ! is part of the directory name
      BufferedReader br = new BufferedReader (new InputStreamReader(is));
      while ((thisLine = br.readLine()) != null) {
         System.out.println(thisLine);
      }
    } catch (Exception e) {
      e.printStackTrace();
    }
  }
}

3. Compile ReadFromJar.java
$ java -version
java version "1.4.1-beta"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.1-beta-b14)
Java HotSpot(TM) Client VM (build 1.4.1-beta-b14, mixed mode)

$ javac ReadFromJar.java

4. Create a jar file and include source and class
$ jar cfv ReadFromJar.jar ReadFromJar*

5. Run the jar file, it should output the source code, but it throws an NullPointerException

$ java -classpath ReadFromJar.jar ReadFromJar
java.lang.NullPointerException
        at java.io.Reader.<init>(Reader.java:61)
        at java.io.InputStreamReader.<init>(InputStreamReader.java:55)
        at ReadFromJar.readTextFromJar(ReadFromJar.java:18)
        at ReadFromJar.<init>(ReadFromJar.java:10)
        at ReadFromJar.main(ReadFromJar.java:6)

6. To see that it is usually working, just move the jar to a different directory
$ mv ReadFromJar.jar /tmp
$ cd /tmp
$ java -classpath ReadFromJar.jar ReadFromJar
import java.io.*;

public class ReadFromJar {

  public static void main(String[] args) {
    new ReadFromJar();
  }
 
  public ReadFromJar() {
     readTextFromJar("ReadFromJar.java");
  }
 
  public void readTextFromJar(String s) {
    String thisLine;
    try {
      InputStream is = getClass().getResourceAsStream(s);
      // returns null if a ! is part of the directory name
      BufferedReader br = new BufferedReader (new InputStreamReader(is));
      while ((thisLine = br.readLine()) != null) {
         System.out.println(thisLine);
      }
    } catch (Exception e) {
      e.printStackTrace();
    }
  }
}