How to Implement a Bitfield Using Java Enums for Document Status Management

How can I implement a bitfield using Java enums to represent document processing statuses?

class DocumentStatus {

    public enum StatusFlag {

        DOCUMENT_STATUS_NOT_DEFINED(1<<0),
        DOCUMENT_STATUS_OK(1<<1), 
        DOCUMENT_STATUS_MISSING_TID_DIR(1<<2),
        DOCUMENT_STATUS_MISSING_TIF_FILE(1<<3),
        DOCUMENT_STATUS_MISSING_PDF_FILE(1<<4),
        DOCUMENT_STATUS_MISSING_OCR_FILE(1<<5),
        DOCUMENT_STATUS_PAGE_COUNT_TIF(1<<6),
        DOCUMENT_STATUS_PAGE_COUNT_PDF(1<<7),
        DOCUMENT_STATUS_UNAVAILABLE(1<<8);

        private final long statusFlagValue;

        StatusFlag(long statusFlagValue) {
            this.statusFlagValue = statusFlagValue;
        }

        public long getStatusFlagValue() {
            return statusFlagValue;
        }
    }
}

Implementing a bitfield using Java enums enhances type safety and clarity in handling multiple document states. This method replaces static integer constants, offering a cleaner and more maintainable approach to status management.

public EnumSet<StatusFlag> getStatusFlags(long statusValue) {
    EnumSet<StatusFlag> statusFlags = EnumSet.noneOf(StatusFlag.class);
    for (StatusFlag statusFlag : StatusFlag.values()) {
        if ((statusFlag.getStatusFlagValue() & statusValue) == statusFlag.getStatusFlagValue()) {
            statusFlags.add(statusFlag);
        }
    }
    return statusFlags;
}

Causes

• Using integer constants can lead to errors and make the code less readable.
• Legacy approaches often lack type safety and are harder to maintain.

Solutions

• Define an enum with specific flag values using bitwise shifting.
• Create methods to convert between numerical values and enum sets for database storage and retrieval.

Mistake: Not using the bitwise operator correctly when checking flag values.

Solution: Ensure you use the bitwise AND (&) operator to accurately determine whether a flag is set.

Mistake: Forgetting to define the enum values properly with shifting operations.

Solution: Always use shifting operations (e.g., 1 << n) for unique power of two values to avoid overlap.