java-native-access/jna · error · IllegalArgumentException

No such field: " + name

Error message

No such field: " + name

What it means

Structure.fieldOffset(String) throws this IllegalArgumentException when the requested name is not a mapped field of the structure. fields() only contains JNA-mapped public instance fields, so any typo or non-mapped member lookup fails after ensureAllocated() runs.

Solutions

1. Correct the field name to exactly match the declared public field (case-sensitive).
2. Make the field public, non-static, non-transient and of a JNA-supported type so it is mapped and gets an offset.
3. Programmatically list valid names first (structure.getFields() / fields().keySet()) to find the right spelling.
4. If the offset of an unmapped member is needed, wrap it in a supported JNA type or compute it manually outside fieldOffset.

Example fix

// before
class Point extends Structure {
    public int x;
    public int y;
}
int off = new Point().fieldOffset("X"); // IllegalArgumentException: No such field: X

// after
int off = new Point().fieldOffset("x");

Set<String> names = structure.getFields().stream().map(Field::getName).collect(Collectors.toSet());
if (!names.contains(name)) {
    throw new IllegalArgumentException(name + " is not a mapped field; valid: " + names);
}

static boolean hasField(Structure s, String name) {
    return s.getFields().stream().anyMatch(f -> f.getName().equals(name));
}

try {
    int off = structure.fieldOffset(name);
} catch (IllegalArgumentException e) {
    // name is not a mapped public field; list valid names for diagnosis
    throw new IllegalArgumentException("valid fields: " + structure.getFields(), e);
}

When it happens

Trigger: Calling structure.fieldOffset("fieldName") with a name that does not exactly match a mapped public field — typos, wrong case, private/protected/static fields, transient fields, or fields of unsupported types that JNA skipped during layout.

Common situations: Hand-writing native offset tables from Java structs; renaming a Java field without updating fieldOffset callers; assuming inherited or private fields participate in the layout.

Understand the failure class

Background: 'Could not be found', 'does not exist', 'not found in database': the resource-not-found family when an ID, slug, key, or URI lookup comes back empty — this error's family across 20 libraries.

Related errors

• Structure size must be greater than zero: " + size
• Array fields must be initialized
• Bad volume GUID path format:
• Byte boundary must be positive
• Can't determine size of nested structure

AI-assisted analysis of java-native-access/jna@d036ad9781 (2026-09-12). Data as JSON: /api/errors/aa0364eb1a88c2ab. Report an issue: GitHub.

Appendix: source

Thrown at src/com/sun/jna/Structure.java:628

            }
        }
        finally {
            busy().remove(this);
            if (this instanceof Structure.ByReference && reading().get(getPointer()) == this) {
                reading().remove(getPointer());
            }
        }
    }

    /** Returns the calculated offset of the given field.
     * @param name field to examine
     * @return return offset of the given field
     */
    protected int fieldOffset(String name) {
        ensureAllocated();
        StructField f = fields().get(name);
        if (f == null) {
            throw new IllegalArgumentException("No such field: " + name);
        }
        return f.offset;
    }

    /** Force a read of the given field from native memory.  The Java field
     * will be updated from the current contents of native memory.
     * @param name field to be read
     * @return the new field value, after updating
     * @throws IllegalArgumentException if no field exists with the given name
     */
    public Object readField(String name) {
        ensureAllocated();
        StructField f = fields().get(name);
        if (f == null)
            throw new IllegalArgumentException("No such field: " + name);
        return readField(f);
    }

View on GitHub (pinned to d036ad9781)