Generate fixed length Strings filled with whitespaces

Question

I need to produce fixed length string to generate a character position based file. The missing characters must be filled with space character.

As an example, the fi

Answer 1

Here is the code with tests cases ;) :

@Test
public void testNullStringShouldReturnStringWithSpaces() throws Exception {
    String fixedString = writeAtFixedLength(null, 5);
    assertEquals(fixedString, "     ");
}

@Test
public void testEmptyStringReturnStringWithSpaces() throws Exception {
    String fixedString = writeAtFixedLength("", 5);
    assertEquals(fixedString, "     ");
}

@Test
public void testShortString_ReturnSameStringPlusSpaces() throws Exception {
    String fixedString = writeAtFixedLength("aa", 5);
    assertEquals(fixedString, "aa   ");
}

@Test
public void testLongStringShouldBeCut() throws Exception {
    String fixedString = writeAtFixedLength("aaaaaaaaaa", 5);
    assertEquals(fixedString, "aaaaa");
}


private String writeAtFixedLength(String pString, int lenght) {
    if (pString != null && !pString.isEmpty()){
        return getStringAtFixedLength(pString, lenght);
    }else{
        return completeWithWhiteSpaces("", lenght);
    }
}

private String getStringAtFixedLength(String pString, int lenght) {
    if(lenght < pString.length()){
        return pString.substring(0, lenght);
    }else{
        return completeWithWhiteSpaces(pString, lenght - pString.length());
    }
}

private String completeWithWhiteSpaces(String pString, int lenght) {
    for (int i=0; i<lenght; i++)
        pString += " ";
    return pString;
}

I like TDD ;)

Answer 2

You can also write a simple method like below

public static String padString(String str, int leng) {
        for (int i = str.length(); i <= leng; i++)
            str += " ";
        return str;
    }

Answer 3

Utilize String.format's padding with spaces and replace them with the desired char.

String toPad = "Apple";
String padded = String.format("%8s", toPad).replace(' ', '0');
System.out.println(padded);

Prints 000Apple.

---

Update more performant version (since it does not rely on String.format), that has no problem with spaces (thx to Rafael Borja for the hint).

int width = 10;
char fill = '0';

String toPad = "New York";
String padded = new String(new char[width - toPad.length()]).replace('\0', fill) + toPad;
System.out.println(padded);

Prints 00New York.

But a check needs to be added to prevent the attempt of creating a char array with negative length.

Answer 4

Since Java 1.5 we can use the method java.lang.String.format(String, Object...) and use printf like format.

The format string "%1$15s" do the job. Where 1$ indicates the argument index, s indicates that the argument is a String and 15 represents the minimal width of the String. Putting it all together: "%1$15s".

For a general method we have:

public static String fixedLengthString(String string, int length) {
    return String.format("%1$"+length+ "s", string);
}

Maybe someone can suggest another format string to fill the empty spaces with an specific character?

Answer 5

The Guava Library has Strings.padStart that does exactly what you want, along with many other useful utilities.

Answer 6

public static String padString(String word, int length) {
    String newWord = word;
    for(int count = word.length(); count < length; count++) {
        newWord = " " + newWord;
    }
    return newWord;
}