java-native-access/jna · error · IllegalArgumentException

Unsupported size

Error message

Unsupported size: <size>

What it means

IntegerType.setValue throws this IllegalArgumentException when the constructor/fromNative path is given a size (in bytes) that is not 1, 2, 4, or 8. IntegerType backs C integer types (uint8_t, int16_t, etc.) and only supports those native widths.

Solutions

1. Use size 1, 2, 4, or 8 matching the actual C type (int8/uint8=1, int16=2, int32=4, int64=8).
2. Fix the subclass constructor super(size) call to a supported width.
3. For sizes not representable, model with a byte array in a Structure or use Memory directly.

Example fix

// before
class UInt24 extends IntegerType { UInt24(int v){ super(3, v); } }
// after
class UInt32 extends IntegerType { UInt32(int v){ super(4, v); } }

static void checkIntegerTypeSize(int size) {
  if (size != 1 && size != 2 && size != 4 && size != 8)
    throw new IllegalArgumentException("IntegerType size must be 1,2,4, or 8, got " + size);
}

try {
  IntegerType v = new MyInt(raw, size);
} catch (IllegalArgumentException e) {
  if (e.getMessage().startsWith("Unsupported size:")) {
    throw new IllegalStateException("Size " + size + " has no IntegerType backing; use 1/2/4/8", e);
  }
  throw e;
}

When it happens

Trigger: Constructing a custom IntegerType subclass with new MyIntegerType(size, value) where size is e.g. 3, 16, or 0; calling fromNative with a FromNativeContext specifying an invalid size; a library returning a size outside {1,2,4,8}.

Common situations: Hand-written IntegerType subclasses for exotic C types (e.g. 3-byte or 128-bit integers); copy-paste errors in the size argument; custom type mappers supplying wrong sizes.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• Argument value 0x exceeds native capacity ( bytes) mask=0x
• Allocation size must be greater than zero
• Area is not polygonal: " + area
• Array fields must be initialized
• Arrays of length zero not allowed: type

AI-assisted analysis of java-native-access/jna@d036ad9781 (2026-09-12). Data as JSON: /api/errors/21ecd7c703923853. Report an issue: GitHub.

Appendix: source

Thrown at src/com/sun/jna/IntegerType.java:104

            case 2:
                if (unsigned) {
                    this.value = value & 0xFFFFL;
                }
                truncated = (short) value;
                this.number = Short.valueOf((short) value);
                break;
            case 4:
                if (unsigned) {
                    this.value = value & 0xFFFFFFFFL;
                }
                truncated = (int) value;
                this.number = Integer.valueOf((int) value);
                break;
            case 8:
                this.number = Long.valueOf(value);
                break;
            default:
                throw new IllegalArgumentException("Unsupported size: " + size);
        }
        if (size < 8) {
            long mask = ~((1L << (size * 8)) - 1);
            if ((value < 0 && truncated != value)
                    || (value >= 0 && (mask & value) != 0)) {
                throw new IllegalArgumentException("Argument value 0x"
                        + Long.toHexString(value) + " exceeds native capacity ("
                        + size + " bytes) mask=0x" + Long.toHexString(mask));
            }
        }
    }

    @Override
    public Object toNative() {
        return number;
    }

    @Override

View on GitHub (pinned to d036ad9781)