JetBrains/intellij-community · error · IllegalArgumentException

attribute '{attributeName}' is not a proper float: {str}

Error message

attribute '{attributeName}' is not a proper float: {str}

What it means

Thrown by LwXmlReader.getRequiredFloat when a required attribute fails Float.parseFloat. Float-valued attributes occur in form layout metadata; a malformed string (non-numeric, comma decimal, trailing units) produces IllegalArgumentException with the attribute name and raw value.

Source

Thrown at java/compiler/forms-compiler/src/com/intellij/uiDesigner/lw/LwXmlReader.java:120

    final String str = element.getAttributeValue(attributeName);
    if (str == null) {
      return defaultValue;
    }
    try {
      return Double.parseDouble(str);
    }
    catch (NumberFormatException e) {
      throw new IllegalArgumentException("attribute '" + attributeName + "' is not a proper double: " + str);
    }
  }

  public static float getRequiredFloat(final Element element, final String attributeName) {
    final String str = getRequiredString(element, attributeName);
    try {
      return Float.parseFloat(str);
    }
    catch (NumberFormatException e) {
      throw new IllegalArgumentException("attribute '" + attributeName + "' is not a proper float: " + str);
    }
  }

  static Object getRequiredPrimitiveTypeValue(final Element element, final String attributeName, final Class valueClass) {
    final String str = getRequiredString(element, attributeName);
    try {
      final Method method = valueClass.getMethod("valueOf", String.class);
      return method.invoke(null, str);
    }
    catch (NumberFormatException e) {
      throw new IllegalArgumentException("attribute '" + attributeName + "' is not a proper float: " + str);
    }
    catch (Exception e) {
      throw new RuntimeException(e);
    }
  }

  static StringDescriptor getStringDescriptor(final Element element, final String valueAttr,

View on GitHub (pinned to be881553f2)

Solutions

  1. Set the attribute to a plain decimal number without suffixes, e.g. "1.5".
  2. If unsure of the expected range, check a designer-saved form using the same component.
  3. Avoid pasting Java source literals into form XML.

Example fix

<!-- before -->
<indent sizeIncr="1.5f"/>

<!-- after -->
<indent sizeIncr="1.5"/>
Defensive patterns

Strategy: validation

Validate before calling

// Validate float-shaped values before parse
if (!str.trim().matches("-?\\d+(\\.\\d+)?([eE][+-]?\\d+)?[fF]?")) throw new IllegalStateException("'" + attr + "' must be a float, got: " + str);
// note: strip a trailing f/F before writing back to XML

Try / catch

try { LwXmlReader.getRequiredFloat(element, attr); } catch (IllegalArgumentException e) { if (e.getMessage().contains("not a proper float")) { /* write a plain decimal without 'f' suffix */ } else throw e; }

Prevention

When it happens

Trigger: A form-XML attribute read via getRequiredFloat holds a value Float.parseFloat rejects — e.g. "thin", "1,5", "12f". Note the parse happens on the trimmed value from getRequiredString, and the attribute itself must already exist or error 53 fires first.

Common situations: Hand-edited form XML with descriptive words in numeric attributes; Java-style float literals pasted in ('1.5f'); locale-edited decimal commas.

Related errors

AI-assisted analysis of JetBrains/intellij-community@be881553f2 (2026-08-14). Data as JSON: /api/errors/79a7c9780e675638. Report an issue: GitHub.