Java adding "0" at the end of the number

Question

So my problem was such that I had to compute 10^n such that n ~ 10^5. Obviously it wouldn't fit in any data type hence I decided to use a string instead. Finally, I did find the solution in the beginners book https://beginnersbook.com/2014/07/java-right-padding-a-string-with-spaces-and-zeros/.

I don't want the BigInteger solution of multiplying 10 n times.

public class PadRightExample2 {
    public static void main(String[] argv) {
        System.out.println("#" + rightPadZeros("mystring", 10) + "@");
        System.out.println("#" + rightPadZeros("mystring", 15) + "@");
        System.out.println("#" + rightPadZeros("mystring", 20) + "@");
    }

    public static String rightPadZeros(String str, int num) {
        return String.format("%1$-" + num + "s", str).replace(' ', '0');
    }
}

Output:

#mystring00@
#mystring0000000@
#mystring000000000000@

Can anybody explain what is %1$- and what is s used for ?

Possible duplicate of [Understanding the $ in Java's format strings](https://stackoverflow.com/questions/1915074/understanding-the-in-javas-format-strings) — ech0, Jul 14 '18 at 11:37
I didn't understand after going through that that's why I asked . — Sushant Pradhan, Jul 14 '18 at 11:42
Did you try reading the [documentation](https://docs.oracle.com/javase/7/docs/api/java/util/Formatter.html) regarding the formatter? — ech0, Jul 14 '18 at 11:45
`Obviuosly it wouldn't fit in any data type` - this is wrong. Use [BigDecimal](https://docs.oracle.com/javase/8/docs/api/java/math/BigDecimal.html) for numbers of any size. — Robert, Jul 14 '18 at 11:50
@Robert Best answer off all! BigDecimal will get as large as you'd like (Until your computer/JVM doesn't run out of memory of course)... You should provide this as answer... Somebody should up vote your comment! — 0x1C1B, Jul 14 '18 at 11:55
@0x1C1B Except that OP want a result like `#mystring0000000@` and `BigDecimal`/`BigInteger` cannot help build that. I mean, Robert is right, `BigDecimal` can be used numbers of any size, but `0000000` is not "a number of any size", since numbers in computers don't have a defined number of leading zeroes. — Andreas, Jul 14 '18 at 12:05
@Andreas Sure but if I understand him right, he just use this because of "no data type would fit" the size of his calculation and that's wrong there is an easier way just use `BigDecimal` and prevent this elaborate and "error-prone" string calculation or Does I understand him wrong? — 0x1C1B, Jul 14 '18 at 12:08
@0x1C1B Yes, you understand wrong, so let me ask you: How would you implement `rightPadZeros("mystring", 15)` to return `mystring0000000` using `BigDecimal`? Because that is what OP wants. — Andreas, Jul 14 '18 at 12:11
@Andreas Yea sure you're right! But I'm sure @Robert wasn't intend to solve the string calculation issue, instead he tried to prevent a elaborate string calculation and solve it in a more efficient way (And you wouldn't deny that `BigDecimal` is the easier way or?)... If you strict try to answer the original question than of course `BigDecimal` isn't a fitting answer you're right — 0x1C1B, Jul 14 '18 at 12:15
@0x1C1B Which was my point in commenting your comment for Robert to write it as an answer. Robert was appropriately commenting that *"wouldn't fit in any data type"* is an incorrect statement, since `BigDecimal` can do that, but `BigDecimal` is not a solution for the problem, and hence is not an answer to the question, so your suggestion to write it as an answer was misguided. — Andreas, Jul 14 '18 at 12:21
@Andreas Last statement: The devil is in the detail. You're right it was a good improvement but **not** a fitting answer — 0x1C1B, Jul 14 '18 at 12:23
I stand corrected . BigDecimal/BigInteger can be used but for this particular case I want to avoid it .I wanted sth which could do the thing in one line . Like I've posted above. — Sushant Pradhan, Jul 14 '18 at 14:09

Nikolas Charalambidis · Accepted Answer · 2018-07-14T12:01:42.693

1

% stands for the format of String
1$ means the first additional parameter args of String.format(String format, Object... args), 2$ would be the second one, etc..
- is the left justification, in connection with number declares the length of the final output, briefly said. The documentation of java.util.Formatter explains is a bit better:

Left justifies the output. Spaces ('\u0020') will be added at the end of the converted value as required to fill the minimum width of the field.
s stands for the String parameter type

The typical example is logging, where you parse the arguments with %s which is practically the same. With a dollar character and number %1$s you specify the argument number and -10 makes the final output length of 10.

#mystring00@            // mystring00 has length 10
#mystring0000000@       // mystring0000000 has length 15
#mystring000000000000@  // #mystring000000000000 has length 20

Most of the information could be found in the documentation of java.util.Formatter, which is used within String::format.

The snippet you have found might be a bit confusing because it works even without 1$ because the arguments are passed in order.

Try the following: String.format("%2$-" + num + "s", str, "test").replace(' ', '0');. The result will be

#test000000@
#test00000000000@
#test0000000000000000@

Whereas String.format("%1$-" + num + "s", str, "test").replace(' ', '0'); leads to the original result from your snippet. Notice the 1$ and 2$ difference.

edited Jul 14 '18 at 12:01

answered Jul 14 '18 at 11:46

Nikolas Charalambidis

40,893
16
117
183

You might want to edit it to say that `s` is actually the parameter type. Would make it simpler for someone who doesn't understand it correctly. – ech0 Jul 14 '18 at 11:47
1

@chromaerror: Right, thanks... that is more precise. – Nikolas Charalambidis Jul 14 '18 at 11:47
the first String argument is "String str" over here? – Sushant Pradhan Jul 14 '18 at 11:48
@SushantPradhan: Yes, that is. – Nikolas Charalambidis Jul 14 '18 at 11:49
@SushantPradhan if you do not know how to distinguish parameters, I would whole-heartedly recommend you to do something more basic, instead of this. For example, going through some basic java tutorials. – ech0 Jul 14 '18 at 11:51
thanks @chromaerror for the advice but I'll pass on it ;) – Sushant Pradhan Jul 14 '18 at 11:53
@SushantPradhan Doesn't sound wise, but do as you please. – ech0 Jul 14 '18 at 11:53
@SushantPradhan: Take a look to the edited part of my answer explaining why you can omit `1$` in your snippet. – Nikolas Charalambidis Jul 14 '18 at 11:56
1

*"`$1` means the first additional parameter"* Didn't you mean `1$`? – Andreas Jul 14 '18 at 12:00
@Andreas: A bunch of typos. Thank you for your eagle eyes :)) – Nikolas Charalambidis Jul 14 '18 at 12:03

Pieter Mantel · Answer 2 · 2018-07-14T12:29:27.967

-1

Maybe I'm not understanding the question correctly, but cant you do:

public static String rightPadZeros(String str, int num) {
    String add = "";
    for(int i = 0; i < num;i++) add += "0";
    return str + add;
}

I dont quite understand why you would want two zeros when num=10, but if you want that, do:

public static String rightPadZeros(String str, int num) {
    String add = "";
    for(int i = 0; i < num - 8;i++) add += "0";
    return str + add;
}

EDIT: apparenetely that was bad for performance, so this might be better:

public static String rightPadZeros(String str, int num) {
    return str + new String(new char[num]).replace("\0", "0");
}

edited Jul 14 '18 at 12:29

answered Jul 14 '18 at 11:43

Pieter Mantel

123
1
9

my num~10^5 so doing this exceeded the time limit constraint of the question . :( – Sushant Pradhan Jul 14 '18 at 11:45
Then you can do `return str + new String(new char[num]).replace("\0", "0");` if you don't want to use a for loop. – Pieter Mantel Jul 14 '18 at 11:55
1

String += String in a loop, 10000 times? Bad for performance. – Andreas Jul 14 '18 at 12:01
Yeah, thats what @SushantPradhan said as well. That's why I improved it. – Pieter Mantel Jul 14 '18 at 12:28
@PieterMantel thanks man ! It's easier to understand than the previous solution ! XD – Sushant Pradhan Jul 15 '18 at 07:18
@SushantPradhan I dont want to take all the credit, I found it [here](https://stackoverflow.com/a/4903603/7132142) – Pieter Mantel Jul 15 '18 at 08:28

Java adding "0" at the end of the number

2 Answers2