What is the simplest way to convert a Java string from all caps (words separated by underscores) to CamelCase (no word separators)?
JavaRegexStringJava Problem Overview
The title pretty much says it all. What's the simplest/most elegant way that I can convert, in Java, a string from the format "THIS_IS_AN_EXAMPLE_STRING" to the format "ThisIsAnExampleString"? I figure there must be at least one way to do it using String.replaceAll() and a regex.
My initial thoughts are: prepend the string with an underscore (_), convert the whole string to lower case, and then use replaceAll to convert every character preceded by an underscore with its uppercase version.
Java Solutions
Solution 1 - Java
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");
Solution 2 - Java
Take a look at WordUtils in the Apache Commons lang library:
Specifically, the capitalizeFully(String str, char[] delimiters) method should do the job:
String blah = "LORD_OF_THE_RINGS";
assertEquals("LordOfTheRings", WordUtils.capitalizeFully(blah, '_').replaceAll("_", ""));
Green bar!
Solution 3 - Java
static String toCamelCase(String s){
String[] parts = s.split("_");
String camelCaseString = "";
for (String part : parts){
camelCaseString = camelCaseString + toProperCase(part);
}
return camelCaseString;
}
static String toProperCase(String s) {
return s.substring(0, 1).toUpperCase() +
s.substring(1).toLowerCase();
}
Note: You need to add argument validation.
Solution 4 - Java
With Apache Commons Lang3 lib is it very easy.
import org.apache.commons.lang3.StringUtils;
import org.apache.commons.lang3.text.WordUtils;
public String getName(String text) {
return StringUtils.remove(WordUtils.capitalizeFully(text, '_'), "_");
}
Example:
getName("SOME_CONSTANT");
Gives:
"SomeConstant"
Solution 5 - Java
Here is a code snippet which might help:
String input = "ABC_DEF";
StringBuilder sb = new StringBuilder();
for( String oneString : input.toLowerCase().split("_") )
{
sb.append( oneString.substring(0,1).toUpperCase() );
sb.append( oneString.substring(1) );
}
// sb now holds your desired String
Solution 6 - Java
Java 1.8 example using Streams
String text = "THIS_IS_SOME_TEXT";
String bactrianCamel = Stream.of(text.split("[^a-zA-Z0-9]"))
.map(v -> v.substring(0, 1).toUpperCase() + v.substring(1).toLowerCase())
.collect(Collectors.joining());
String dromedaryCamel = bactrianCamel.toLowerCase().substring(0, 1) + bactrianCamel.substring(1);
System.out.printf("%s is now %s%n", text, dromedaryCamel);
THIS_IS_SOME_TEXT is now thisIsSomeText
Solution 7 - Java
public static void main(String[] args) {
String start = "THIS_IS_A_TEST";
StringBuffer sb = new StringBuffer();
for (String s : start.split("_")) {
sb.append(Character.toUpperCase(s.charAt(0)));
if (s.length() > 1) {
sb.append(s.substring(1, s.length()).toLowerCase());
}
}
System.out.println(sb);
}
Solution 8 - Java
The Apache Commons project does now have the CaseUtils class, which has a toCamelCase method that does exactly as OP asked:
CaseUtils.toCamelCase("THIS_IS_AN_EXAMPLE_STRING", true, '_');
Solution 9 - Java
You can use org.modeshape.common.text.Inflector.
Specifically:
> String camelCase(String lowerCaseAndUnderscoredWord, > boolean uppercaseFirstLetter, char... delimiterChars) > > By default, this method converts strings to UpperCamelCase.
Maven artifact is: org.modeshape:modeshape-common:2.3.0.Final
on JBoss repository: https://repository.jboss.org/nexus/content/repositories/releases
Here's the JAR file: https://repository.jboss.org/nexus/content/repositories/releases/org/modeshape/modeshape-common/2.3.0.Final/modeshape-common-2.3.0.Final.jar
Solution 10 - Java
Not sure, but I think I can use less memory and get dependable performance by doing it char-by-char. I was doing something similar, but in loops in background threads, so I am trying this for now. I've had some experience with String.split being more expensive then expected. And I am working on Android and expect GC hiccups to be more of an issue then cpu use.
public static String toCamelCase(String value) {
StringBuilder sb = new StringBuilder();
final char delimChar = '_';
boolean lower = false;
for (int charInd = 0; charInd < value.length(); ++charInd) {
final char valueChar = value.charAt(charInd);
if (valueChar == delimChar) {
lower = false;
} else if (lower) {
sb.append(Character.toLowerCase(valueChar));
} else {
sb.append(Character.toUpperCase(valueChar));
lower = true;
}
}
return sb.toString();
}
A hint that String.split is expensive is that its input is a regex (not a char like String.indexOf) and it returns an array (instead of say an iterator because the loop only uses one things at a time). Plus cases like "AB_AB_AB_AB_AB_AB..." break the efficiency of any bulk copy, and for long strings use an order of magnitude more memory then the input string.
Whereas looping through chars has no canonical case. So to me the overhead of an unneeded regex and array seems generally less preferable (then giving up possible bulk copy efficiency). Interested to hear opinions / corrections, thanks.
Solution 11 - Java
public String withChars(String inputa) {
String input = inputa.toLowerCase();
StringBuilder sb = new StringBuilder();
final char delim = '_';
char value;
boolean capitalize = false;
for (int i=0; i<input.length(); ++i) {
value = input.charAt(i);
if (value == delim) {
capitalize = true;
}
else if (capitalize) {
sb.append(Character.toUpperCase(value));
capitalize = false;
}
else {
sb.append(value);
}
}
return sb.toString();
}
public String withRegex(String inputa) {
String input = inputa.toLowerCase();
String[] parts = input.split("_");
StringBuilder sb = new StringBuilder();
sb.append(parts[0]);
for (int i=1; i<parts.length; ++i) {
sb.append(parts[i].substring(0,1).toUpperCase());
sb.append(parts[i].substring(1));
}
return sb.toString();
}
Times: in milli seconds.
Iterations = 1000
WithChars: start = 1379685214671 end = 1379685214683 diff = 12
WithRegex: start = 1379685214683 end = 1379685214712 diff = 29
Iterations = 1000
WithChars: start = 1379685217033 end = 1379685217045 diff = 12
WithRegex: start = 1379685217045 end = 1379685217077 diff = 32
Iterations = 1000
WithChars: start = 1379685218643 end = 1379685218654 diff = 11
WithRegex: start = 1379685218655 end = 1379685218684 diff = 29
Iterations = 1000000
WithChars: start = 1379685232767 end = 1379685232968 diff = 201
WithRegex: start = 1379685232968 end = 1379685233649 diff = 681
Iterations = 1000000
WithChars: start = 1379685237220 end = 1379685237419 diff = 199
WithRegex: start = 1379685237419 end = 1379685238088 diff = 669
Iterations = 1000000
WithChars: start = 1379685239690 end = 1379685239889 diff = 199
WithRegex: start = 1379685239890 end = 1379685240585 diff = 695
Iterations = 1000000000
WithChars: start = 1379685267523 end = 1379685397604 diff = 130081
WithRegex: start = 1379685397605 end = 1379685850582 diff = 452977
Solution 12 - Java
You can Try this also :
public static String convertToNameCase(String s)
{
if (s != null)
{
StringBuilder b = new StringBuilder();
String[] split = s.split(" ");
for (String srt : split)
{
if (srt.length() > 0)
{
b.append(srt.substring(0, 1).toUpperCase()).append(srt.substring(1).toLowerCase()).append(" ");
}
}
return b.toString().trim();
}
return s;
}
Solution 13 - Java
protected String toCamelCase(String input) {
if (input == null) {
return null;
}
if (input.length() == 0) {
return "";
}
// lowercase the first character
String camelCaseStr = input.substring(0, 1).toLowerCase();
if (input.length() > 1) {
boolean isStartOfWord = false;
for (int i = 1; i < input.length(); i++) {
char currChar = input.charAt(i);
if (currChar == '_') {
// new word. ignore underscore
isStartOfWord = true;
} else if (Character.isUpperCase(currChar)) {
// capital letter. if start of word, keep it
if (isStartOfWord) {
camelCaseStr += currChar;
} else {
camelCaseStr += Character.toLowerCase(currChar);
}
isStartOfWord = false;
} else {
camelCaseStr += currChar;
isStartOfWord = false;
}
}
}
return camelCaseStr;
}
Solution 14 - Java
public String CamelCase(String str)
{
String CamelCase="";
String parts[] = str.split("_");
for(String part:parts)
{
String as=part.toLowerCase();
int a=as.length();
CamelCase = CamelCase + as.substring(0, 1).toUpperCase()+ as.substring(1,a);
}
return CamelCase;
}
This is the Simplest Program to convert into CamelCase. hope it Will Help You..
Solution 15 - Java
public static String toCamelCase(String value) {
value = value.replace("_", " ");
String[] parts = value.split(" ");
int i = 0;
String camelCaseString = "";
for (String part : parts) {
if (part != null && !part.isEmpty()) {
if (i == 0) {
camelCaseString = part.toLowerCase();
} else if (i > 0 && part.length() > 1) {
String oldFirstChar = part.substring(0, 1);
camelCaseString = camelCaseString + part.replaceFirst(oldFirstChar, oldFirstChar.toUpperCase());
} else {
camelCaseString = camelCaseString + part + " ";
}
i++;
}
}
return camelCaseString;
}
public static void main(String[] args) {
String string = "HI_tHiS_is_SomE Statement";
System.out.println(toCamelCase(string));
}
Solution 16 - Java
Sorry for mine five cents, I think in java too many words)) I just wondering. Why is the regexp engine in java not so familiar with lambdas as in JS((
Anyway. With java 8+ construction appears in my mind:
Arrays.stream("THIS_IS_AN_EXAMPLE_STRING".split("_"))
.collect(StringBuilder::new,
(result, w) -> result
.append(w.substring(0, 1).toUpperCase())
.append(w.substring(1).toLowerCase()),
StringBuilder::append)
.toString())
If you care about memory consumption, the below code care about it:
"THIS_IS_AN_EXAMPLE_STRING".chars().collect(StringBuilder::new,
(result, c) -> {
// Detect place for deal with
if (result.length() > 0 && result.charAt(result.length() - 1) == '_') {
result.setCharAt(result.length() - 1,
Character.toUpperCase((char) c));
} else if (result.length() > 0) {
result.append(Character.toLowerCase((char) c));
} else {
result.append(Character.toUpperCase((char) c));
}
}, StringBuilder::append).toString()
Solution 17 - Java
It will convert Enum Constant into Camel Case. It would be helpful for anyone who is looking for such funtionality.
public enum TRANSLATE_LANGUAGES {
ARABIC("ar"), BULGARIAN("bg"), CATALAN("ca"), CHINESE_SIMPLIFIED("zh-CN"), CHINESE_TRADITIONAL("zh-TW"), CZECH("cs"), DANISH("da"), DUTCH("nl"), ENGLISH("en"), ESTONIAN("et"), FINNISH("fi"), FRENCH(
"fr"), GERMAN("de"), GREEK("el"), HAITIAN_CREOLE("ht"), HEBREW("he"), HINDI("hi"), HMONG_DAW("mww"), HUNGARIAN("hu"), INDONESIAN("id"), ITALIAN("it"), JAPANESE("ja"), KOREAN("ko"), LATVIAN(
"lv"), LITHUANIAN("lt"), MALAY("ms"), NORWEGIAN("no"), PERSIAN("fa"), POLISH("pl"), PORTUGUESE("pt"), ROMANIAN("ro"), RUSSIAN("ru"), SLOVAK("sk"), SLOVENIAN("sl"), SPANISH("es"), SWEDISH(
"sv"), THAI("th"), TURKISH("tr"), UKRAINIAN("uk"), URDU("ur"), VIETNAMESE("vi");
private String code;
TRANSLATE_LANGUAGES(String language) {
this.code = language;
}
public String langCode() {
return this.code;
}
public String toCamelCase(TRANSLATE_LANGUAGES lang) {
String toString = lang.toString();
if (toString.contains("_")) {
String st = toUpperLowerCase(toString.split("_"));
}
return "";
}
private String toUpperLowerCase(String[] tempString) {
StringBuilder builder = new StringBuilder();
for (String temp : tempString) {
String char1 = temp.substring(0, 1);
String restString = temp.substring(1, temp.length()).toLowerCase();
builder.append(char1).append(restString).append(" ");
}
return builder.toString();
}
}
Solution 18 - Java
One more solution to this may be as follows.
public static String toCamelCase(String str, String... separators) {
String separatorsRegex = "\\".concat(org.apache.commons.lang3.StringUtils.join(separators, "|\\"));
List splits = Arrays.asList(str.toLowerCase().split(separatorsRegex));
String capitalizedString = (String)splits.stream().map(WordUtils::capitalize).reduce("", String::concat);
return capitalizedString.substring(0, 1).toLowerCase() + capitalizedString.substring(1);
}
Solution 19 - Java
public static final String UPPER_CAMEL = "initUp";
public static final String LOWER_CAMEL = "initLow";
public String toCamel(String src, String separator, String format) {
StringBuilder builder = new StringBuilder(src.toLowerCase());
int len = builder.length();
for (int idx = builder.indexOf(separator); idx > 0 && idx < len; idx = builder.indexOf(separator, idx)) {
builder = builder.replace(idx, idx + 2, (String.valueOf(builder.charAt(idx + 1)).toUpperCase()));
}
switch (format) {
case LOWER_CAMEL:
builder.setCharAt(0, Character.toLowerCase(builder.charAt(0)));
break;
default:
builder.setCharAt(0, Character.toUpperCase(builder.charAt(0)));
break;
}
return builder.toString();
}
Invocation as
toCamel("THIS_IS_AN_EXAMPLE_STRING", "_", UPPER_CAMEL)
Execution Time: 14 ms
Solution 20 - Java
A simple snnipet:
public static String camelCase(String in) {
if (in == null || in.length() < 1) { return ""; } //validate in
String out = "";
for (String part : in.toLowerCase().split("_")) {
if (part.length() < 1) { //validate length
continue;
}
out += part.substring(0, 1).toUpperCase();
if (part.length() > 1) { //validate length
out += part.substring(1);
}
}
return out;
}
Solution 21 - Java
protected String toCamelCase(CaseFormat caseFormat, String... words){
if (words.length == 0){
throw new IllegalArgumentException("Word list is empty!");
}
String firstWord = words[0];
String [] restOfWords = Arrays.copyOfRange(words, 1, words.length);
StringBuffer buffer = new StringBuffer();
buffer.append(firstWord);
Arrays.asList(restOfWords).stream().forEach(w->buffer.append("_"+ w.toUpperCase()));
return CaseFormat.UPPER_UNDERSCORE.to(caseFormat, buffer.toString());
}
Solution 22 - Java
Java 8 for multiple strings:
import com.google.common.base.CaseFormat;
String camelStrings = "YOUR_UPPER, YOUR_TURN, ALT_TAB";
List<String> camelList = Arrays.asList(camelStrings.split(","));
camelList.stream().forEach(i -> System.out.println(CaseFormat.UPPER_UNDERSCORE.to(CaseFormat.UPPER_CAMEL, i) + ", "));