java - 为什么我不能将变量作为格式字符串传递给 Java 中的 System.out.printf (...)？

Question

我试图在 Java 中将字符串对象传递给 System.out.printf(...)，但我一直收到此错误 "java.util.FormatFlagsConversionMismatchException: Conversion = s, Flags = 0" 这对我来说实际上没有多大意义。

String format = "%" + (3 * n) + "s"; // n is an int defined somewhere above, could be 0
System.out.printf(format, "My string");

有人知道这是否被允许吗？

编辑更多细节:

int n = 0;
String fm = "%" + (3 * level) + "s";
String realFm = "%0s";
System.out.println("fm = " + fm);
System.out.println("realfm = " + realFm);
System.out.println("equals? " + (fm.equals(realFm)));
System.out.printf(fm, " ");

这是输出:

fm = %0s
realfm = %0s
equals? true
java.util.FormatFlagsConversionMismatchException: Conversion = s, Flags = 0

谢谢

Answer 1

是的，它是允许的，但如果 n 为 0 则它不会起作用。是否有可能发生这种情况(从错误消息看起来像)？

如果你在代码中添加一行来调试它会怎样:

// line added below for debugging. To remove later:
System.out.println("n is: " + n); 

String format = "%" + (3 * n) + "s"; // n is an int defined somewhere above
System.out.printf(format, "My string");

它是否打印过 n is: 0?

例如，

public static void main(String[] args) {

  // try the for loop with n = 0 vs. n = 1
  for (int n = 1; n <= 10; n++) {
     // line added below for debugging. To remove later:
     System.out.println("\nn is: " + n); 

     String format = "%" + (3 * n) + "s"; 
     System.out.printf(format, "My string");
  }      
}