public static String javaNameFromExternal(final String externalName) {
        requireNonNull(externalName);
        return replaceIfIllegalJavaIdentifierCharacter(replaceIfJavaUsedWord(nameFromExternal(externalName)));
    }
Turns the specified string into an underscore-separated string.

@param javaName  the string to parse
@return          as underscore separated
common-parent/codegen/src/main/java/com/speedment/common/codegen/util/Formatting.java