Enums that cross reference each other produce different results depending on order called

Question

I have two enums that cross reference each other. Each one has a constructor that has a parameter for other enum.

They look something like:

SchoolEnum(ImmuneEnum value)
{
   this.immune = value;
}

ImmuneEnum(SchoolEnum value)
{
   this.school = value;
}

However depending on which Enum I call first, I can get a null value for the reference variable.

ImmunityEnum immune = ImmunityEnum.IMMUNE_KANNIC; 
SchoolEnum school = SchoolEnum.KANNIC;
System.out.println(school.getImmune())
System.out.println(immune.getSchool());

Produces the output: null Kannic

SchoolEnum school = SchoolEnum.KANNIC;
ImmunityEnum immune = ImmunityEnum.IMMUNE_KANNIC; 
System.out.println(school.getImmune())
System.out.println(immune.getSchool());

Produces the output: immunekannic null

It seems to be a bit of the "chicken and egg" problem as to when the enum is instantiated. But is there a way to have each one properly reference the other? I am considering making two singleton hashmaps that artificially cross reference the two, but is there a better idea?

Answer 1

What if you passing String parameters into your constructors:

public enum SchoolEnum {
   Kannic("immnunekannic");
   private String immune;
   public SchoolEnum (String immune) {this.immune = immune;}
   public ImmuneEnum getImmune() {
       return ImmuneEnum.valueOf(immune);
   }
}

public enum ImmnueEnum {
   immunekannic("Kannic");
   private String scholl;
   public ImmnueEnum (String school) {this.school = school;}
   public SchoolEnum getSchool() {
       return SchoolEnum.valueOf(school);
   }
}

But honestly it's a bit strange to create this type of domain model. What's your use case?

Answer 2

It's not the prettiest solution in the world, but how about setting the cross-references afterwards?:

enum SchoolEnum {
    KANNIC;
    private ImmunityEnum immune;
    public ImmunityEnum getImmune() {
        return immune;
    }
    public void setImmune(ImmunityEnum immune) {
        this.immune = immune;
    }
}

enum ImmunityEnum {
    IMMUNE_KANNIC;
    private SchoolEnum school;
    public SchoolEnum getSchool() {
        return school;
    }
    public void setSchool(SchoolEnum school) {
        this.school = school;
    }
}

Now use it like this:

SchoolEnum school = SchoolEnum.KANNIC;
school.setImmune(ImmunityEnum.IMMUNE_KANNIC);
ImmunityEnum immune = ImmunityEnum.IMMUNE_KANNIC; 
immune.setSchool(SchoolEnum.KANNIC);

System.out.println(school.getImmune());
System.out.println(immune.getSchool());

Answer 3

public enum SchoolEnum  {
  KANNIC {

    @Override
    public ImmunityEnum  getImmune() {
      return ImmunityEnum.IMMUNE_KANNIC;
    }
  };

  public abstract ImmunityEnum getImmune();
}

public enum ImmunityEnum {
  IMMUNE_KANNIC {

    @Override    
    public SchoolEnum getSchool() {
      return SchoolEnum.KANNIC;
    }
  };

  public abstract SchoolEnum getSchool();
}