The specification of DecimalFormat states:

 Prefix:
         any Unicode characters except \uFFFE, \uFFFF, and special characters
 Suffix:
         any Unicode characters except \uFFFE, \uFFFF, and special characters

However, the implementation allows suffix with special characters like "#".

For example:

import java.text.*;

public class DecimalFormatTest01 {

    public static void main (String[] args) {
        String pattern1 = "###,000.000suffix2##";
        DecimalFormat df = new DecimalFormat();
        try {
            df.applyPattern(pattern1);
            System.out.println("FAILED: IllegalArgumentException expected for pattern " + pattern1);
            System.out.println("Suffix: " + df.getPositiveSuffix());
        } catch (IllegalArgumentException iae) {
            // OKAY
        }
    }
}

Output in JDK 6.0:

FAILED: IllegalArgumentException expected for pattern ###,000.000suffix2##
Suffix: suffix2