[Java] Align characters even with mixed half-width and full-width characters

Introduction

When using String # format in Java with a mixture of half-width and full-width characters, the character position may shift. Even if I looked up too much, there was no easy way to solve it, so I tried to build a function.

solution

Immediately, but the solution is as follows. (For the time being, just copy and paste the following format () and getByteLength () to solve the problem)

main

    public static void main(String[] args){
        //Shift format statement
        System.out.println(String.format("%-20s", "Ahhhh")+" | ");
        System.out.println(String.format("%-20s", "aaaaa")+" | ");
        //Format statement that does not shift
        System.out.println(format("Ahhhh", 20)+" | ");
        System.out.println(format("aaaaa", 20)+" | ");
    }

    private static String format(String target, int length){
        int byteDiff = (getByteLength(target, Charset.forName("UTF-8"))-target.length())/2;
        return String.format("%-"+(length-byteDiff)+"s", target);
    }

    private static int getByteLength(String string, Charset charset) {
        return string.getBytes(charset).length;
    }

result

Ahhhh| 
aaaaa                | 
Ahhhh| 
aaaaa                | 

(It is a secret that | was misaligned when copying and pasting to Qiita ...) The following is a digression.

Reasons for deviation and countermeasures

In the first place, the reason why there is a difference between half-width and full-width is that the number of bytes differs as follows when expressing characters with ʻUTF-8`.

• Japanese: 3byte
• Alphanumeric characters: 1 byte

So, I am adjusting with ʻint byte Diff in main`. Also, from the following function, you can see that Japanese is 3 bytes and English is 1 byte.

analyze

    public static void main(String[] args){
        analyze("Ahhhh");
        analyze("aaaaa");
    }

    private static void analyze(String target){
        System.out.println("\n"+target);
        int length=20;
        System.out.println(format("length()", length)+":"+target.length());
        System.out.println(format("UTF-8 length()", length)+":"+getByteLength(target, Charset.forName("UTF-8")));
        System.out.println(format("diff", length)+":"+(getByteLength(target, Charset.forName("UTF-8"))-target.length())/2);
    }

result

Ahhhh
length()            :5
UTF-8 length()      :15
diff                :5

aaaaa
length()            :5
UTF-8 length()      :5
diff                :0

reference

• Java: How to fill in zeros and spaces
• Get the number of bytes in [Java] String