试题4

import java.math.BigInteger;

public class Test {
    public static void main(String [] args){
        BigInteger one = new BigInteger("1");
        BigInteger two = new BigInteger("2");
        BigInteger three = new BigInteger("3");
        BigInteger sum = new BigInteger("0");
        sum.add(one);
        sum.add(two);
        sum.add(three);
        System.out.println(sum.toString());
    }
}

输出结果：0

由于sum.add() 后面没有赋值，结果不会改变，还是0.