==========$ cat -n T.java
     1 class T {
     2 public static void main(String[] args) {
     3 System.out.printf("%c%n", 1237817231);
     4 }
     5 }
==========$ /java/re/j2se/1.5.0/promoted/latest/binaries/`platform`/bin/java -version
java version "1.5.0-beta2"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0-beta2-b47)
Java HotSpot(TM) Client VM (build 1.5.0-beta2-b47, mixed mode)
==========$ /java/re/j2se/1.5.0/promoted/latest/binaries/`platform`/bin/javac -source 1.5 T.java
==========$ /java/re/j2se/1.5.0/promoted/latest/binaries/`platform`/bin/java T
Exception in thread "main" ==========$

The reason is that IllegalFormatCodePointException.getmessage() throws a
fresh copy of IllegalFormatCodePointException.