Java printf: How define/declare empty spaces through a Conversion implicitly?

Question

In Java having the following

printf("%-5s Hello %s %n", "", "There!")

It prints

     Hello There!

Where exists 5 empty spaces located to the left.

Until here it works how is expected, but ...

I want to know if is possible: How avoid the "" declaration and change %-5s to something that printf can interpret that represents an empty space?

I mean: for example %-5e where e is assumed to represent an empty character and therefore is not necessary anymore declare "" explicitly.

Something similar like %n where it does not required an argument through the printf. Is clear that %s requires an argument, in this case "" but being curious if my request can be accomplished.

I read the Formatter javadoc for that required feature and seems does not exist.

I already did do a research on SO and some suggested solutions is use the + within printf, but to be honest it reduces readability

Therefore the goal is (formatted for better presentation):

From: printf("%-5s Hello %s %n", "", "There!")
To:   printf("%-5e Hello %s %n",     "There!") // %-5e is the functionality I need or looking for

All you want is a way to print 5 spaces before Hello There!. How about System.out.printf(" ".repeat(5) + " Hello %s %n", "There!");? — Arvind Kumar Avinash
– Arvind Kumar Avinash, Commented Jun 20, 2020 at 14:21
Is possible do that without use +? I don't want lost readability — Manuel Jordan
– Manuel Jordan, Commented Jun 20, 2020 at 14:31
In fact, even my previous comment is not applicable in your case as you are using Java-8 (I just saw one of your comments). In order to make it easier for future visitors to this question, I've tagged it with Java-8 now. — Arvind Kumar Avinash
– Arvind Kumar Avinash, Commented Jun 20, 2020 at 16:12
Is this really carrying the intended semantics? What about printf("%11s %s %n", "Hello", "There!")? — Holger
– Holger, Commented Jun 22, 2020 at 11:37
Your approach is totally valid, proceed to put it how the answer, to be marked by my side. — Manuel Jordan
– Manuel Jordan, Commented Jun 22, 2020 at 14:00

Eritrean · Accepted Answer · 2020-06-20 14:50:23Z

1

If you are using Java 12 or higher and all you need is to adjusts the indentation of the resulting string, you could use String#indent. Using your example to insert 5 spaces at the beginning:

System.out.printf("Hello %s %n".indent(5),  "There!");

Since indent also normalizes line termination characters, you could also remove %n

System.out.printf("Hello %s ".indent(1),  "There!");
System.out.printf("Hello %s ".indent(2),  "There!");
System.out.printf("Hello %s ".indent(3),  "There!");
System.out.printf("Hello %s ".indent(4),  "There!");

to get something like:

 Hello There! 
  Hello There! 
   Hello There! 
    Hello There!

edited Jun 20, 2020 at 14:50

answered Jun 20, 2020 at 14:38

Eritrean

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score 0 · Accepted Answer · 2020-06-20 15:53:24Z

0

You should define new printf like this.

static Pattern EMPTY_CONVERSION = Pattern.compile("%-?(\\d+)e");

public static String printf(String format, Object... args) {
    StringBuffer sb = new StringBuffer();
    Matcher m = EMPTY_CONVERSION.matcher(format);
    while (m.find())
        m.appendReplacement(sb, " ".repeat(Integer.parseInt(m.group(1))));
    m.appendTail(sb);
    return String.format(sb.toString(), args);
}

If you use Java 8, make your own repeat.

e is reserved for floating point conversions, so you might want to change it.

edited Jun 20, 2020 at 15:53

answered Jun 20, 2020 at 15:39

user4910279

1 Comment

Manuel Jordan Over a year ago

I understand, "e" was just a representation, could be any character ... "%anything"

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