Puzzle (What’s my class, Take 2)

package demo;

import java.io.File;

public class App {
  public static void main( String[] args ) {
    String name = App.class.getName().replaceAll( "\\.", File.separator ) + ".class";
    System.out.println( name );
  }
}

Java is said to be write once and run everywhere and that’s true, if you avoid some corner cases. The above will fail on a Windows operating system.

Exception in thread "main" StringIndexOutOfBoundsException: String index out of range: 1
  at java.lang.String.charAt(String.java:558)
  at java.util.regex.Matcher.appendReplacement(Matcher.java:696)
  at java.util.regex.Matcher.replaceAll(Matcher.java:806)
  at java.lang.String.replaceAll(String.java:2000)
  at com.javapuzzlers.MeToo.main(MeToo.java:6)

This example was taken from PUZZLE 21: WHAT’S MY CLASS, TAKE 2 in Java™ Puzzlers: Traps, Pitfalls, and Corner Cases.

“Although this behavior is platform dependent, it isn’t exactly what we were looking for. What went wrong on Windows? It turns out that the second parameter of String.replaceAll() is a not an ordinary string but a replacement string, as defined in the java.util.regex specification (Java-API). A backslash appearing in a replacement string escapes the following character, causing it to be treated literally. When you run the program on Windows, the replacement string is a lone backslash character, which is invalid. Admittedly, the exception could be a little more informative.”