java - 我计算光行进距离的代码出错

Question

我需要编写一个程序，生成 5 行输出，显示程序运行时自 Unix 纪元以来光(在真空中)传播的距离。

1. 字符串:“自 Unix 纪元以来，光已经传播......”。
2. 公里数(假设光速恰好为 299792458 m/s):x.xxx 公里。
3. 天文单位数，假设 149597870700.0 m/au:x.xxx au。
4. 光年数，假设 9460730472580800.0 m/ly:x.xxx ly。
5. 秒差距数，假设为 3.085677581e16 m/pc(请注意，3.085677581e16 是 Java 用普通科学记数法表示 3.085677581⋅10^16 的方式):x.xxx 电脑。

在我的代码中，我收到整数过高的错误，并且在使用 print 方法时遇到问题。有人可以帮忙吗？

我收到的错误是:

 Assignment02.java:16: error: integer number too large: 9460730472580
     long ly = km / 9460730472580;
                    ^
Assignment02.java:20: error: ')' expected
        "Since the Unix epoch, light has traveled..."
                                                     ^
Assignment02.java:25: error: not a statement
        (km), au, ly, pc);
         ^
Assignment02.java:25: error: ';' expected
        (km), au, ly, pc);
           ^
Assignment02.java:25: error: not a statement
        (km), au, ly, pc);
              ^
Assignment02.java:25: error: ';' expected
        (km), au, ly, pc);
                ^
Assignment02.java:25: error: not a statement
        (km), au, ly, pc);
                  ^
Assignment02.java:25: error: ';' expected
        (km), au, ly, pc);
                    ^
Assignment02.java:25: error: not a statement
        (km), au, ly, pc);
                      ^
Assignment02.java:25: error: ';' expected
        (km), au, ly, pc);

这是我的代码:

public class Assignment02  {

  public static void main (String[] args)  {

    // Stores the return value of System.currentTimeMillis() in variab$
    long now = System.currentTimeMillis();
    // Calculation of how far light has travelled until "now" in kilometer$
    long km = (299792 * now)/1000 ;
    // Calculatuion of how far light has travelled until "now" in astronomical units$
    long au =  km / 149597870;
    // Calculation of how far light has travelled until "now" in light years$
    long ly = km / 9460730472580;
    // Calculation of how far light has traveled until "now" in parsecs
    long pc = km / 3.085677581e16;
    System.out.printf(
      "Since the Unix epoch, light has traveled..."+
      "%d km"+
      "%d au"+
      "%d ly"+
      "%d pc",
      (km), au, ly, pc);

  }

}

Answer 1

您可以像这样修复编译错误并打印语句:

• 在大整数值末尾添加了 L，使其成为 long 文字。
• 添加了对 long 的强制转换以转换 double 值。
• 添加了 %n 来打印格式字符串，以便在输出中添加换行符。

long now = System.currentTimeMillis();
long km = (299792 * now)/1000 ;
long au =  km / 149597870;
long ly = km / 9460730472580L;
long pc = (long) (km / 3.085677581e16);
System.out.printf("Since the Unix epoch, light has traveled...%n"+
                  "%d km%n"+
                  "%d au%n"+
                  "%d ly%n"+
                  "%d pc",
                  (km), au, ly, pc);

当然，您可能实际上想要输出double值，而不是long值:

long now = System.currentTimeMillis();
long km = (299792 * now)/1000 ;
long au =  km / 149597870;
double ly = km / 9460730472580d;
double pc = km / 3.085677581e16;
System.out.printf("Since the Unix epoch, light has traveled...%n"+
                  "%d km%n"+
                  "%d au%n"+
                  "%.1f ly%n"+
                  "%f pc",
                  (km), au, ly, pc);

输出

Since the Unix epoch, light has traveled...
451349163977648 km
3017082 au
47.7 ly
0.014627 pc