C中％04X的含义以及如何在java中编写相同内容

Question

In the java project i am working on, some portion of the project was written previously by someone else in C and now i need to write the same in Java.

There is a statement in C code for printing to a file:

fprintf(ff, "%04X ", image[y*width+x]);

Firstly i am not sure about the meaning of %04X . I think it means that if image[i] has length five or more then print only leftmost four chararacters. To do the same in Java i thought about masking the value using and operation

 image[i] & 0xFFFF

Can someone please tell me the correct meaning of %04X and how to do the same in Java? Thanks.

Answer 1

The value is formatted as a hexadecimal integer with four digits and leading zeros. Java uses the same format string syntax. You can find it in the javaDoc of Formatter .

Excerpt:

'x', 'X'     integral    The result is formatted as a hexadecimal integer

A related functions are

// create a String with the formatted value.
String formatted = String.format("%04X ", image[y*width+x]);

// write a formatted value to the console (*)
System.out.printf("%04X ", image[y*width+x]);

_{(*) - write it to the PrintStream System.out which is usually the console but can be redirected to a file or something else}

Answer 2

Lets break the format code "%04X" into its separate parts:

• The X means that it will print an integer, in hexadecimal, large X for large hexadecimal letters
• The 4 means the number will be printed left justified with at least four digits, print spaces if there is less than four digits
• The 0 means that if there is less than four digits it will print leading zeroes.

Answer 3

The X in %04X means hexadecimal, with ABCDEF instead of abcdef, and the 04 means print at least four digits, padding with leading zeros. It will use more digits if needed.