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));
    }
}