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

Question

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");

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!

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.

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"

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

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