我在理解这个Java如何使用我正在提供它的参数时遇到了问题

Question

我遇到的问题是在运行命令时理解这段代码:java Driver 1000000它返回:sum(1000000)= 1784293664

无论我试图看多久,我都无法理解为什么以及代码如何做到这一点我只是想知道是否有人可以提供任何帮助来理解这些代码实际对数字做了什么？

class Sum
{
  private int sum;

  public int get() {
    return sum;
  }

  public void set(int sum) {
    this.sum = sum;
  }
}

class Summation implements Runnable
{
  private int upper;
  private Sum sumValue;

  public Summation(int upper, Sum sumValue) {
    this.upper = upper;
    this.sumValue = sumValue;
  }

  public void run() {
    int sum = 0;

    for (int i = 0; i <= upper; i++)
      sum += i;

    sumValue.set(sum);
  }
}

public class Driver
{
  public static void main(String[] args) {
    if (args.length != 1) {
      System.err.println("Usage Driver <integer>");
      System.exit(0);
    }

    if (Integer.parseInt(args[0]) < 0) {
      System.err.println(args[0] + " must be >= 0");
      System.exit(0);
    }

    // Create the shared object
    Sum sumObject = new Sum();
    int upper = Integer.parseInt(args[0]);

    Thread worker = new Thread(new Summation(upper, sumObject));
    worker.start();

    try {
      worker.join();
    } catch (InterruptedException ie) { }
    System.out.println("sum(" + upper + ") = " + sumObject.get());
  }
}

提前致谢

安德鲁

Answer 1

总结数字1到1百万:

(1 + 1000000) * 1000000 / 2 = 500000500000

这会导致int你用来保存总和的溢出.结果是:

500000500000 (mod 2^32) = 1784293664

用a long来存储总和; 它具有最大值9223372036854775807并且可以保持总和.