How to Convert Camelcase into Human-Readable Names in Java

How do I convert CamelCase into human-readable names in Java?

This works with your testcases:

static String splitCamelCase(String s) {
   return s.replaceAll(
      String.format("%s|%s|%s",
         "(?<=[A-Z])(?=[A-Z][a-z])",
         "(?<=[^A-Z])(?=[A-Z])",
         "(?<=[A-Za-z])(?=[^A-Za-z])"
      ),
      " "
   );
}

Here's a test harness:

    String[] tests = {
        "lowercase",        // [lowercase]
        "Class",            // [Class]
        "MyClass",          // [My Class]
        "HTML",             // [HTML]
        "PDFLoader",        // [PDF Loader]
        "AString",          // [A String]
        "SimpleXMLParser",  // [Simple XML Parser]
        "GL11Version",      // [GL 11 Version]
        "99Bottles",        // [99 Bottles]
        "May5",             // [May 5]
        "BFG9000",          // [BFG 9000]
    };
    for (String test : tests) {
        System.out.println("[" + splitCamelCase(test) + "]");
    }

It uses zero-length matching regex with lookbehind and lookforward to find where to insert spaces. Basically there are 3 patterns, and I use String.format to put them together to make it more readable.

The three patterns are:

UC behind me, UC followed by LC in front of me

  XMLParser   AString    PDFLoader
    /\        /\           /\

non-UC behind me, UC in front of me

 MyClass   99Bottles
  /\        /\

Letter behind me, non-letter in front of me

 GL11    May5    BFG9000
  /\       /\      /\

References

regular-expressions.info/Lookarounds

How do I convert underscore into human-readable names in Java?

A naive way of accomplishing this would be to replace every '_' with a ' ', and then trim the whitespaces off the final string:

public static String splitUnderscore(String s) {
    return s.replace("_", " ").trim();
}

While the above works for most cases, to handle multiple adjacent underscores we could use a regular expression to replace any number of consecutive underscores with a single ' ':

public static String splitUnderscore(String s) {
    return s.replaceAll("_{1,}", " ").trim();
}

How do I convert CamelCase into human-readable Title Case in VBScript?

Probably an easier way to do this, but this should give you the results you're looking for.

MsgBox SplitCamelCase ("lowercase")         ' Returns: "lowercase"
MsgBox SplitCamelCase ("Class")             ' Returns: "Class"
MsgBox SplitCamelCase ("My Class")          ' Returns: "My Class"
MsgBox SplitCamelCase ("HTML")              ' Returns: "HTML"
MsgBox SplitCamelCase ("PDF Loader")        ' Returns: "PDF Loader"
MsgBox SplitCamelCase ("A String")          ' Returns: "A String"
MsgBox SplitCamelCase ("Simple XML Parser") ' Returns: "Simple XML Parser"
MsgBox SplitCamelCase ("GL 11 Version")     ' Returns: "GL 11 Version"
MsgBox SplitCamelCase ("CSDVersionCamel")   ' Returns: "CSD Version Camel"

Function SplitCamelCase(strTxt)
    Dim strNew, i

    strNew = ""

    For i = 1 To Len(strTxt)

        If Mid(strTxt, i, 1) = " " Then
            strNew = strNew & Mid(strTxt, i, 1)
        ElseIf IsNumeric(Mid(strTxt, i, 1)) Then
            If i > 1 Then
                If IsNumeric(Mid(strTxt, i - 1, 1)) Then
                    strNew = strNew & Mid(strTxt, i, 1)
                ElseIf Mid(strTxt, i - 1, 1) = " " Then
                    strNew = strNew & Mid(strTxt, i, 1)
                Else
                    strNew = strNew & " " & Mid(strTxt, i, 1)
                End If
            Else
                strNew = strNew & " " & Mid(strTxt, i, 1)
            End If
        ElseIf Mid(strTxt, i, 1) = UCase(Mid(strTxt, i, 1)) Then
            If i > 1 Then               
                If Mid(strTxt, i - 1, 1) = UCase(Mid(strTxt, i - 1, 1)) Then
                    If Mid(strTxt, i + 1, 1) = " " Then 
                        strNew = strNew & Mid(strTxt, i, 1)
                    ElseIf Mid(strTxt, i + 1, 1) = "" Then 
                        strNew = strNew & Mid(strTxt, i, 1) 
                    ElseIf IsNumeric(Mid(strTxt, i + 1, 1)) = True Then 
                        strNew = strNew & Mid(strTxt, i, 1)
                    ElseIf Mid(strTxt, i + 1, 1) = LCase(Mid(strTxt, i + 1, 1)) Then
                        If Mid(strTxt, i - 1, 1) = " " Then
                            strNew = strNew & Mid(strTxt, i, 1)
                        Else
                            strNew = strNew & " " & Mid(strTxt, i, 1)
                        End If
                    Else
                        strNew = strNew & Mid(strTxt, i, 1)
                    End If
                ElseIf Mid(strTxt, i - 1, 1) <> " " Then            
                    strNew = strNew & " " & Mid(strTxt, i, 1)
                Else
                    strNew = strNew & Mid(strTxt, i, 1)
                End If
            Else
                strNew = strNew & Mid(strTxt, i, 1)
            End If
        Else
            strNew = strNew & Mid(strTxt, i, 1)
        End If  
    Next

    SplitCamelCase = Trim(strNew)

End Function

What is the simplest way to convert a Java string from all caps (words separated by underscores) to CamelCase (no word separators)?

Another option is using Google Guava's com.google.common.base.CaseFormat

George Hawkins left a comment with this example of usage:

CaseFormat.UPPER_UNDERSCORE.to(CaseFormat.UPPER_CAMEL, "THIS_IS_AN_EXAMPLE_STRING");

Regex for converting CamelCase to camel_case in java

See this question and CaseFormat from guava

in your case, something like:

CaseFormat.UPPER_CAMEL.to(CaseFormat.LOWER_UNDERSCORE, "SomeInput");

Need to convert underscore separated words into human readable form?

Using java-8 you can do so in a single line :

String str = "NAME_OF_THINGS";

Arrays.stream(str.replaceAll("_", " ").toLowerCase().split(" "))
      .map(s -> Character.toUpperCase(s.charAt(0)) + s.substring(1) + " ")
      .forEach(System.out::print);

Here we replace all occurences of _ with " " and then convert the entire string to lowercase. Next we split it based on " " and then perform sub-string operation to achieve the result.

This gives the output :

Name Of Things

To get only the first letter capitalized use:

String newString = Character.toUpperCase(str.charAt(0)) + str.substring(1)
                            .replaceAll("_", " ").toLowerCase();

This gives :

Name of things

Convert camelCaseText to Title Case Text

const text = 'helloThereMister';
const result = text.replace(/([A-Z])/g, " $1");
const finalResult = result.charAt(0).toUpperCase() + result.slice(1);
console.log(finalResult);

How can I convert camelCase to a string with spaces? (e.g. camelCase to Camel Case)

#rereplace("camelCaseString","([A-Z])"," \1","all")#

edit: the version below will handle the lowercase first character.

#rereplace(rereplace("camelCaseString","(^[a-z])","\u\1"),"([A-Z])"," \1","all")#

How do I convert a camelCase string to underscore in java keeping some upper cases and the rests as lower cases?

You can use Matcher#appendReplacement and pass dynamic replacement, based on what was found by regex.

I also changed your regex a little bit, to not include lowercase part in match, but accept only uppercase character which is preceded by lowercase character. More info at: http://www.regular-expressions.info/lookaround.html

String text = "Hi How areYouToday";
Matcher m = Pattern.compile("(?<=[a-z])[A-Z]").matcher(text);

StringBuffer sb = new StringBuffer();
while (m.find()) {
    m.appendReplacement(sb, "_"+m.group().toLowerCase());
}
m.appendTail(sb);

System.out.println(sb.toString()); //Hi How are_you_today

OR Since Java 9

Matcher m = Pattern.compile("(?<=[a-z])[A-Z]").matcher(text);
String result = m.replaceAll(match -> "_" + match.group().toLowerCase());

because construct

StringBuffer sb = new StringBuffer();
while(m.find()){
    m.appendReplacement(sb, /*replacement for each match*/);
}
m.appendTail(sb);
String result = sb.toString();

was wrapped into Matcher#replaceAll(Function replacer) so it can be used as

String result = m.replaceAll( (MatchResult match) -> /*replacement for each match*/ );

How to convert camelCase to Camel Case?

"thisStringIsGood"
    // insert a space before all caps
    .replace(/([A-Z])/g, ' $1')
    // uppercase the first character
    .replace(/^./, function(str){ return str.toUpperCase(); })

displays

This String Is Good

(function() {
  const textbox = document.querySelector('#textbox')  const result = document.querySelector('#result')  function split() {      result.innerText = textbox.value        // insert a space before all caps        .replace(/([A-Z])/g, ' $1')        // uppercase the first character        .replace(/^./, (str) => str.toUpperCase())    };
  textbox.addEventListener('input', split);  split();}());

#result {  margin-top: 1em;  padding: .5em;  background: #eee;  white-space: pre;}

<div>  Text to split  <input id="textbox" value="thisStringIsGood" /></div>
<div id="result"></div>