Question

This is a simplified example. I have this enum declaration as follows:

public enum ELogLevel {
    None,
    Debug,
    Info,
    Error
}

I have this code in another class:

if ((CLog._logLevel == ELogLevel.Info) || (CLog._logLevel == ELogLevel.Debug) || (CLog._logLevel == ELogLevel.Error)) {
    System.out.println(formatMessage(message));
}

My question is if there is a way to shorten the test. Ideally i would like somethign to the tune of (this is borrowed from Pascal/Delphi):

if (CLog._logLevel in [ELogLevel.Info, ELogLevel.Debug, ELogLevel.Error])

Instead of the long list of comparisons. Is there such a thing in Java, or maybe a way to achieve it? I am using a trivial example, my intention is to find out if there is a pattern so I can do these types of tests with enum value lists of many more elements.

EDIT: It looks like EnumSet is the closest thing to what I want. The Naïve way of implementing it is via something like:

if (EnumSet.of(ELogLevel.Info, ELogLevel.Debug, ELogLevel.Error).contains(CLog._logLevel))

But under benchmarking, this performs two orders of magnitude slower than the long if/then statement, I guess because the EnumSet is being instantiated every time it runs. This is a problem only for code that runs very often, and even then it’s a very minor problem, since over 100M iterations we are talking about 7ms vs 450ms on my box; a very minimal amount of time either way.

What I settled on for code that runs very often is to pre-instantiate the EnumSet in a static variable, and use that instance in the loop, which cuts down the runtime back down to a much more palatable 9ms over 100M iterations.

So it looks like we have a winner! Thanks guys for your quick replies.

Answer 1

what you want is an enum set

http://docs.oracle.com/javase/1.5.0/docs/api/java/util/EnumSet.html

put the elements you want to test for in the set, and then use the Set method contains().

import java.util.EnumSet;


public class EnumSetExample
{
  enum Level { NONE, DEBUG, INFO, ERROR };

  public static void main(String[] args)
  {
    EnumSet<Level> subset = EnumSet.of(Level.DEBUG, Level.INFO);

    for(Level currentLevel : EnumSet.allOf(Level.class))
    {
      if (subset.contains(currentLevel))
      {
        System.out.println("we have " + currentLevel.toString());
      }
      else
      {
        System.out.println("we don't have " + currentLevel.toString());
      }
    }
  }

}