权限Demo

一个小demo

public class BigIntegerTest {    public static void main(String[] args) {        BigInteger num = new BigInteger("0");            num = num.setBit(2);            num = num.setBit(1);            System.out.println(num);            System.out.println(num.testBit(2));            System.out.println(num.testBit(1));            System.out.println(num.testBit(3));    }}