Commons Lang、BitField#isSet()

import org.apache.commons.lang.BitField;

public class C2009042800 {
    public static void main(String[] args) {
        BitField bf;

        bf = new BitField(5);
        System.out.println(bf.isSet(1));

        bf = new BitField(5);
        System.out.println(bf.isSet(2));

        bf = new BitField(5);
        System.out.println(bf.isSet(4));


        bf = new BitField(5);
        System.out.println(bf.isSet(15));

        bf = new BitField(7);
        System.out.println(bf.isSet(15));

        bf = new BitField(7);
        System.out.println(bf.isSet(7));

        bf = new BitField(15);
        System.out.println(bf.isSet(7));

        bf = new BitField(5);
        System.out.println(bf.isSet(10));
    }
}

で、

true
false
true
true
true
true
true
false