Question

我无法让BigInteger为其添加另一个BigInteger。有什么建议相关代码：

在课堂上宣布：

private BigInteger mTotientSum;

在构造函数中完成：

BigInteger mTotientSum = BigInteger.ZERO;

相对方法：

  BigInteger totientMultiplier = BigInteger.valueOf(mTotientMulitplier);
  for (long i = 1; i <= mMaxNum; i++)
  {
     BigInteger j = BigInteger.valueOf(i);
     System.out.println(j.toString());
     BigInteger num = j.multiply(totientMultiplier);
     System.out.println(num.toString());
     BigInteger totient = calculateTotient(num);
     System.out.println(totient);
     mTotientSum = mTotientSum.add(totient); //This is line 113
     System.out.println("Sum at" + i + " = " + mTotientSum.toString());
  }

我得到的输出是：

1
510510
17
16
16
Exception in thread "main" java.lang.NullPointerException
          at Totient.run(Totient.java:113) (Note that line 113 is noted above.)
      at Totient.main(Totient.java:131)

Answer 1

您正在构造函数中隐藏变量。致电

BigInteger mTotientSum = BigInteger.ZERO;

您只是初始化本地mTotientSum变量并将类字段保留为null。

不要在构造函数中重新声明变量。而是做：

mTotientSum = BigInteger.ZERO;

看到区别？

BigInteger抛出空指针异常

1 个答案: