Question

I’m new to using Java Enums and I’ve read that replace IF logic that compares String literals should be replaced with an Enum. I don’t quite understand how to replace my below code with an Enum, any ideas? Based on the col value being passed into applyEQ, I need to do a base the next method call on it’s value. I do know the possible values of col ahead of time and I’m using a constants file for now. Should I create an Enum and place it in my Interface of Constants file?

public class FilterHelper implements IFilterHelper {

   private final EQuery eQuery;

   public FilterHelper(EQuery query) {
      eQuery = query;
   }

    @Override
    public void applyEQ(String col, String val) throws Exception {
        int return = 0;
        if (col.equalsIgnoreCase(EConstants.NAME)) {
            ret = Sample.addName(eQuery, val);
        } else if (col.equalsIgnoreCase(EConstants.KEYWORDS)) {
            ret = Sample.addKey(eQuery, val);
        } else if (col.equalsIgnoreCase(EConstants.ROLE)) {
            ret = Sample.addRole(eQuery, val);
        }  

        if (return != 0) {
            throw new Exception("failed");
        }
    }
}

EConstants.java

public final class EConstants {    
    public static final String NAME = "cewName";
    public static final String KEYWORDS = "cewKeywords";
    public static final String ROLE = "cewRole";
}

Answer 1

First create an enum:

public enum EConstants {
    CEWNAME,
    CEWROLE,
    CEWKEYWORDS;
}

Then convert col String to this enum and use switch:

public void applyEQ(String col, String val) throws Exception {
    int ret = 0;
    final EConstants constant = EConstants.valueOf(col.toUpperCase());
    switch(constant) {
        case CEWNAME:
            ret = Sample.addName(eQuery, val);
            break;
        case CEWROLE:
            ret = Sample.addRole(eQuery, val);
            break;
        case CEWKEYWORDS:
            ret = Sample.addKey(eQuery, val);
            break;
        default:
            throw new Exception("Unhandled enum constant: " + constant);
    }
}

Note that EConstants.valueOf() can throw IllegalArgumentException if col.toUpperCase() does not match any of constant values.

BTW I hate local variables initialized in multiple places (and break keyword), try extracting method:

final EConstants constant = EConstants.valueOf(col.toUpperCase());
final int ret = processSample(val, constant);

And the method itself:

private int processSample(String val, EConstants constant) throws Exception {
    switch(constant) {
        case CEWNAME:
            return Sample.addName(eQuery, val);
        case CEWROLE:
            return Sample.addRole(eQuery, val);
        case CEWKEYWORDS:
            return Sample.addKey(eQuery, val);
        default:
            throw new Exception("Unhandled enum constant: " + constant);
    }
}