==========$ cat -n T.java
     1 import java.math.BigDecimal;
     2
     3 class T {
     4 public static void main(String[] args) {
     5 System.out.printf("%a %n", new BigDecimal("12.3"));
     6 }
     7 }
==========$ ../j2se/build/linux-i586/j2sdk-image/bin/javac T.java
==========$ ../j2se/build/linux-i586/j2sdk-image/bin/java -esa T
Exception in thread "main" java.util.IllegalFormatConversionException: a != java.math.BigDecimal
        at java.util.Formatter$FormatSpecifier.failConversion(Formatter.java:3899)
        at java.util.Formatter$FormatSpecifier.print(Formatter.java:3410)
        at java.util.Formatter$FormatSpecifier.printFloat(Formatter.java:2699)
        at java.util.Formatter$FormatSpecifier.print(Formatter.java:2647)
        at java.util.Formatter.format(Formatter.java:2415)
        at java.io.PrintStream.format(PrintStream.java:899)
        at java.io.PrintStream.printf(PrintStream.java:800)
        at T.main(T.java:5)
==========$