How to Pad a String in Java

How can I pad a String in Java?

Apache StringUtils has several methods: leftPad, rightPad, center and repeat.

But please note that — as others have mentioned and demonstrated in this answer — String.format() and the Formatter classes in the JDK are better options. Use them over the commons code.

Left padding a String with Zeros

If your string contains numbers only, you can make it an integer and then do padding:

String.format("%010d", Integer.parseInt(mystring));

If not I would like to know how it can be done.

Java pad string with specific characters

Other way how you can do it:

String.format("%8s", "helllo").replace(' ', '*');

In this case you do not need to add library.

Java pad string with space

Hope this might help

    String email = "abc@jhkj.com";
    System.out.println(String.format("Home:%1$3s%s%s", "", email));

Output:
Home: abc@jhkj.com

How to pad Strings with Unicode characters in Java

There are actually a few issues here, other than that some fonts display the flag wider than the other characters. I assume that you want to count the Chinese flag as a single character (as it is drawn as a single element on the screen).

The String class reports an incorrect length

The String class works with chars, which are 16-bit integers of Unicode code points. The problem is that not all code points fit in 16 bits, only code points from the Basic Multilingual Plane (BMP) fit in those chars. String's length() method returns the number of chars, not the number of code points.

Now String's codePointCount method may help in this case: it counts the number of code points in the given index range. So providing string.length() as second argument to the method returns the total count of code points.

Combining characters

However, there's another problem. The Chinese flag, for example, consists of two Unicode code points: the Regional Indicator Symbol Letters C (, U+1F1E8) and N (, U+1F1F3). Those two code points are combined into a flag of China. This is a problem you are not going to solve with the codePointCount method.

The Regional Indicator Symbol Letters seem to be a special occasion. Two of those characters can be combined into a national flag. I am not aware of a standard way to achieve what you want. You may have to take that manually into account.

I've written a small program to get the length of a string.

static int length(String str) {
    String a = "\uD83C\uDDE6";
    String z = "\uD83C\uDDFF";

    Pattern p = Pattern.compile("[" + a + "-" + z + "]{2}");
    Matcher m = p.matcher(str);
    int count = 0;
    while (m.find()) {
        count++;
    }
    return str.codePointCount(0, str.length()) - count;
}

How to pad a formatted string

What is it about "msg" that does not let me pad it?

It's longer than 10 characters.

That 10 is the width of the Formatter class.

Reading that documentation, you'll see

The optional width is a non-negative decimal integer indicating the minimum number of characters to be written to the output.

So, minimum, meaning any string longer than that are printed as-is.

If you want to pad, just add 10 to the length of the string.

String msg = "some really, really long message";
String fmt = "%1$" + (10 + msg.length()) + "s";
String pad = String.format(fmt, msg);
// "          some really, really long message"

Java padding a string read from a file

A simple solution:

public static String pad_num(String line){
    String[] groups = line.split("-");
    String left = groups[0],
            right = groups[1];

    if(left.length() < right.length()) {
        do {
            left = '0'+left;
        } while (left.length() < right.length());
    } else if(right.length() < left.length()) {
        do {
            right = '0'+right;
        } while (right.length() < left.length());
    }

    return left+'-'+right;
}

---

If you don't have fixed operator, you can pass it as an argument:

public static String pad_num(String line, String operator){
    //prevent ArrayIndexOutOfBoundsException
    if(!line.contains(operator)) {
        return line;
    }

    //prevent PatternSyntaxException by compiling it as literal
    String[] groups = Pattern.compile(operator, Pattern.LITERAL).split(line);

    //do the same
    ...

    return left+operator+right;
}

how to string pad with variables instead of hard coded numbers inside %s in java

You could use "%-"+namePad+"s" instead of "%-5s"

Although, I am unsure you really need that variable at all. You are using String.format, but giving no variables to format, so try this instead.

String.format("%d - %-21s", id, name);

Or, as before

int pad = 21;
return String.format("%d - %-"+pad+"s*", id, name);

---

For example, (with the * added to show the padding)

static class Person {
    int id;
    String name;

    public Person(int id, String name) {
        this.id = id; this.name = name;
    }

    public String toString() {
        return String.format("%d - %-21s*", id, name);
    }
}

public static void main (String[] args) throws java.lang.Exception
{
    Person[] people = { 
        new Person(1, "Bill Gates"),
        new Person(2, "Trump"),
        new Person(3, "Tail"), 
        new Person(4, "James Bond")
    };

    for (Person p : people) {
        System.out.println(p);
    }
}

Output

1 - Bill Gates           *
2 - Trump                *
3 - Tail                 *
4 - James Bond           *

---

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