FULL PRODUCT VERSION :
java version "1.8.0_05"
Java(TM) SE Runtime Environment (build 1.8.0_05-b13)
Java HotSpot(TM) 64-Bit Server VM (build 25.5-b02, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows [Version 6.3.9600]

A DESCRIPTION OF THE PROBLEM :
java.text.MessageFormat selects wrong format from the array of formats, which can result in an exception being thrown. Please see "Source code for an executable test case" below. The code + actual/expected result show the issue clearly.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Please see "Source code for an executable test case" below

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
There are no files on C:\.
There is one file on C:\.
There are 2 files on C:\.
ACTUAL -
Exception in thread "main" java.lang.IllegalArgumentException: Cannot format given Object as a Number
at java.text.DecimalFormat.format(DecimalFormat.java:507)
at java.text.Format.format(Format.java:157)
at java.text.MessageFormat.subformat(MessageFormat.java:1322)
at java.text.MessageFormat.format(MessageFormat.java:865)
at java.text.Format.format(Format.java:157)
at bugreports.MessageFormatBug.main(MessageFormatBug.java:26)

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.util.*;
import java.text.*;

public class MessageFormatBug {

public static void main(String[] args) {
MessageFormat messageFmt = new MessageFormat("");
messageFmt.setLocale(Locale.ENGLISH);
messageFmt.applyPattern("There {0} on {2}.");

double[] fileLimits = {0, 1, 2};
String[] fileStrings = { "are no files", "is one file", "are {1} files" };
ChoiceFormat choiceFmt = new ChoiceFormat(fileLimits, fileStrings);

Format[] formats = {choiceFmt, NumberFormat.getInstance(), null};

messageFmt.setFormats(formats);

Object[] messageArguments = {null, null, "C:\\"};

for (int nbFiles = 0; nbFiles < 3; nbFiles++) {
messageArguments[0] = nbFiles;
messageArguments[1] = nbFiles;
System.out.println(messageFmt.format(messageArguments));
}
}

}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
In java.text.MessageFormat ( this version: http://hg.openjdk.java.net/jdk8u/jdk8u/jdk/file/4bb758a77fd7/src/share/classes/java/text/MessageFormat.java#l1259 ), changing formats[i] to formats[argumentNumber] on lines 1259, 1260, 1262 solves the problem & correctly prints the expected result.