Separation of words by capital letters-CodePudding

How to add space between words, without importing a library? Each word starts with a capital letter.

input:

HowAreYou

output:

how are you

This is my attempt which is not working:

public static String capSpace(String txt) {
    String word = null;
    for (int i = 0; i < txt.length(); i  ) {
        int a = txt.charAt(i);
        String g = " ";
        if (a == Character.toUpperCase(a)) {
            word = txt.substring(0, i)   " "   txt.substring(i);
        }
    }
    return word;
}

CodePudding user response：

I think you were on the right track, but we can simplify your logic a bit. Consider every character in txt. If it is uppercase (and not the first character) add a space, then add the lowercase version of the character. Otherwise add the character. Like,

public static String capSpace(String txt) {
    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < txt.length(); i  ) {
        char ch = txt.charAt(i);
        if (i != 0 && Character.isUpperCase(ch)) {
            sb.append(" ");
        }
        sb.append(Character.toLowerCase(ch));
    }
    return sb.toString();
}

And then to test it,

public static void main(String[] args) {
    System.out.println(capSpace("HowAreYou"));
}

Which outputs (as requested)

how are you

CodePudding user response：

Do not forget about performance. You should not modify String in a loop, because every iteration you create a new string. It's much better to use StringBuilder:

public static String capSpace(String str) {
    StringBuilder buf = new StringBuilder();

    for (int i = 0; i < str.length(); i  ) {
        char ch = str.charAt(i);

        if (Character.isUpperCase(ch) && buf.length() > 0)
            buf.append(' ');

        buf.append(Character.toLowerCase(ch));
    }

    return buf.toString();
}

CodePudding user response：

Stream.of("HowAreYou".split("(?=\\p{Upper})"))
    .map(String::toLowerCase)
    .collect(Collectors.joining(" "));

CodePudding user response：

Use String::replaceAll with a regular expression (?<!^)\p{Lu} selecting all uppercase letters except for the first letter in the string to insert the space, and then call String::toLowerCase to change the case of entire String at once (which should have better performance than lower-casing characters one by one):

public static String capSpace(String txt) {
    if (null == txt || txt.isEmpty()) {
        return txt;
    }
    return txt.replaceAll("(?<!^)\\p{Lu}", " $0").toLowerCase();
}

Tests:

System.out.println("|"   capSpace("HelloHowAreYou")   "|");

Output:

|hello how are you|

CodePudding user response：

You can split and then use static method String.join():

public static String capSpace(String str) {
    return String.join(" ", str.split("(?=[A-Z])")).toLowerCase();
}

Then:

String str = "HowAreYou";
    
System.out.println(capSpace(str));

Output:

how are you