soappatrol soappatrol - 1 month ago 21
Java Question

Implementing a bitfield using java enums

I maintain a large document archive and I often use bit fields to record the status of my documents during processing or when validating them. My legacy code simply uses static int constants such as:

static int DOCUMENT_STATUS_NO_STATE = 0
static int DOCUMENT_STATUS_OK = 1
static int DOCUMENT_STATUS_NO_TIF_FILE = 2
static int DOCUMENT_STATUS_NO_PDF_FILE = 4


This makes it pretty easy to indicate the state a document is in, by setting the appropriate flags. For example:

status = DOCUMENT_STATUS_NO_TIF_FILE | DOCUMENT_STATUS_NO_PDF_FILE;


Since the approach of using static constants is bad practice and because I would like to improve the code, I was looking to use Enums to achieve the same. There are a few requirements, one of them being the need to save the status into a database as a numeric type. So there is a need to transform the enumeration constants to a numeric value. Below is my first approach and I wonder if this is the correct way to go about this?

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
}

}


/**
* Translates a numeric status code into a Set of StatusFlag enums
* @param numeric statusValue
* @return EnumSet representing a documents status
*/
public EnumSet<StatusFlag> getStatusFlags(long statusValue)
{
EnumSet statusFlags = EnumSet.noneOf(StatusFlag.class)
StatusFlag.each { statusFlag ->
long flagValue = statusFlag.statusFlagValue
if ( (flagValue&statusValue ) == flagValue )
{
statusFlags.add(statusFlag)
}
}

return statusFlags
}


/**
* Translates a set of StatusFlag enums into a numeric status code
* @param Set if statusFlags
* @return numeric representation of the document status
*/
public long getStatusValue(Set<StatusFlag> flags)
{
long value=0
flags.each { statusFlag ->

value|=statusFlag.getStatusFlagValue()
}

return value
}

public static void main(String[] args) {

DocumentStatus ds = new DocumentStatus();
Set statusFlags = EnumSet.of(
StatusFlag.DOCUMENT_STATUS_OK,
StatusFlag.DOCUMENT_STATUS_UNAVAILABLE)

assert ds.getStatusValue( statusFlags )==258 // 0000.0001|0000.0010

long numericStatusCode = 56
statusFlags = ds.getStatusFlags(numericStatusCode)

assert !statusFlags.contains(StatusFlag.DOCUMENT_STATUS_OK)
assert statusFlags.contains(StatusFlag.DOCUMENT_STATUS_MISSING_TIF_FILE)
assert statusFlags.contains(StatusFlag.DOCUMENT_STATUS_MISSING_PDF_FILE)
assert statusFlags.contains(StatusFlag.DOCUMENT_STATUS_MISSING_OCR_FILE)

}

}

Answer

your approach is exactly the way to do it.

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