JetBrains/intellij-community · warning · ConfigurationException

Not a valid java identifier part in prefix '{0}'

Error message

Not a valid java identifier part in prefix '{0}'

What it means

setPrefixSuffix in the Java code-style generation settings validates the 'Name prefix'/'Name suffix' fields: after trimming, a non-empty value must be a full Java identifier (StringUtil.isJavaIdentifier). If it is not, a ConfigurationException is thrown with this message, so the Settings dialog reports the field in error and refuses to apply. The prefix/suffix is spliced into generated identifiers (e.g. 'my' prefix -> 'myField'), hence the identifier constraint.

Source

Thrown at java/java-impl/src/com/intellij/application/options/CodeStyleGenerationConfigurable.java:569

    javaSettings.REPLACE_SUM = myReplaceSumCb.isSelected();


    myCommenterForm.apply(settings);
    javaSettings.setRepeatAnnotations(myRepeatAnnotationsModel.getItems());

    for (Project project : ProjectManager.getInstance().getOpenProjects()) {
      DaemonCodeAnalyzer.getInstance(project).settingsChanged();
    }
  }

  private static String setPrefixSuffix(String text, boolean prefix) throws ConfigurationException {
    text = text.trim();
    if (text.isEmpty()) return text;
    if (!StringUtil.isJavaIdentifier(text)) {
      final @Nls String message = JavaBundle.message(prefix
                                                     ? "code.style.generation.settings.error.not.valid.identifier.part.in.prefix"
                                                     : "code.style.generation.settings.error.not.valid.identifier.part.in.suffix", text);
      throw new ConfigurationException(message);
    }
    return text;
  }

  @Override
  public void apply() throws ConfigurationException {
    apply(mySettings);
  }

  public boolean isModified(CodeStyleSettings settings) {
    JavaCodeStyleSettings javaSettings = settings.getCustomSettings(JavaCodeStyleSettings.class);
    boolean isModified = isCheckboxModified(myCbPreferLongerNames, javaSettings.PREFER_LONGER_NAMES);

    isModified |= isFieldModified(myFieldPrefixField, javaSettings.FIELD_NAME_PREFIX);
    isModified |= isFieldModified(myStaticFieldPrefixField, javaSettings.STATIC_FIELD_NAME_PREFIX);
    isModified |= isFieldModified(myParameterPrefixField, javaSettings.PARAMETER_NAME_PREFIX);
    isModified |= isFieldModified(myLocalVariablePrefixField, javaSettings.LOCAL_VARIABLE_NAME_PREFIX);
    isModified |= isFieldModified(mySubclassPrefix, javaSettings.SUBCLASS_NAME_PREFIX);

View on GitHub (pinned to be881553f2)

Solutions

1. Enter only characters legal in a Java identifier: letters, digits (not first), '$' and '_' — e.g. 'my' or 'm'.
2. Clear the field entirely if you do not want a prefix/suffix (empty is accepted after trim).
3. Remember the value is prepended/appended verbatim to generated member names, so keep it a plain identifier fragment.

Example fix

// before (Settings input, rejected)
name prefix: "my."

// after
name prefix: "my"

// Before calling apply() programmatically or writing settings:
String prefix = myPrefixField.getText().trim();
if (!prefix.isEmpty() && !com.intellij.openapi.util.text.StringUtil.isJavaIdentifier(prefix)) {
  Messages.showErrorDialog("Name prefix must be a valid Java identifier", "Invalid Input");
  return;
}

try { configurable.apply(); } catch (ConfigurationException e) { Messages.showErrorDialog(e.getMessage(), "Cannot Apply"); }

When it happens

Trigger: Typing a non-identifier value such as 'my.', 'a-b', '1x', or 'get()' into Settings | Editor | Code Style | Java | Code Generation name prefix/suffix fields and pressing Apply/OK.

Common situations: Trying to use a dotted or hyphenated prefix; pasting text with trailing punctuation; attempting to simulate a full naming scheme (e.g. 'mFoo') that is not a bare identifier.

Related errors

• ''{0}'' is invalid extracted class name
• ''{0}'' is invalid field name for delegation
• ''{0}'' is invalid parameter name
• ''{0}'' is invalid inner class name
• ''{0}'' is invalid parameter class name

AI-assisted analysis of JetBrains/intellij-community@be881553f2 (2026-08-14). Data as JSON: /api/errors/be474ff0f16b1cc0. Report an issue: GitHub.