java - System.out.format 的输出 ("%6f%n", 123.0);不符合预期

Question

我目前正在学习如何用java进行格式化，遇到了以下问题

我有

System.out.format("%6f%n", 123.0);

我期望结果为 123.0，左侧有一个空格(即输出的最小长度为 6)。然而，我却得到了

123.000000 //with no blank space on the left 

为什么会发生这种情况？为什么小数点后有六个0？有人可以向我解释一下吗？

Answer 1

您需要指定小数点后面的位数。如果不这样做，则假定为 6 位数字。所以你可以这样做:

System.out.format("%6.1f%n", 123.0);

来自Javadoc :

The number of digits in the result for the fractional part of m or a is equal to the precision. If the precision is not specified then the default value is 6. If the precision is less than the number of digits which would appear after the decimal point in the string returned by Float.toString(float) or Double.toString(double) respectively, then the value will be rounded using the round half up algorithm. Otherwise, zeros may be appended to reach the precision.