Java中的初学者 - 字符串格式=“| ％ - ” + maxW [J] +的‘s’; - 这个字符串做什么？

Question

I am a noob in Java and I came across the code below and couldn't figure out its function. maxw[] is an array of type int. row[] is an array of type String.

             String format = " | %-"+maxW[i]+"s";
       System.out.printf(format,row[i]);

My questions is : For this statement : System.out.printf(format,row[i]); only '|' and after that value of row[i] are getting printed so why are '%- (value of maxW[i]) and 's' not getting printed ?

Answer 1

Java format specifiers are described here .

This code is dynamically creating a format specifier that will left-justify a string (row[i]) with a minimum width specified by maxW[i].

Format specifiers follow the pattern on the first line below. Underneath I've aligned the code above, showing where it fits into the pattern.

    %[argument_index$][flags] [width] [.precision]conversion
" | %                  -     "+maxW[i]           +"s";

Answer 2

The format method assumes the String decribes a format as it states in the documentation. It handles %x or the like a special way replacing it with the first, second etc argument.

If you want to know more I suggest you read the Javadoc for this method.