Commons Lang、BitField#getShortRawValue(), #getShortValue()

import org.apache.commons.lang.BitField;

public class C2009042600 {
    public static void main(String[] args) {
        BitField bf;

        bf = new BitField(5);
        System.out.println(bf.getShortRawValue((short)15) + " " + bf.getShortValue((short)15));

        bf = new BitField(4);
        System.out.println(bf.getShortRawValue((short)15) + " " + bf.getShortValue((short)15));
    }
}

で、

5 5
4 1