Custom fields on java enum not getting serialized

Question

I have a Java Enum as shown below:

public enum ExecutionMode {
  TYPE_A,
  TYPE_B,
  TYPE_C;

  private ExecutionMode(){} //no args constr- no really require         


        

Answer 1

If the values are constant, this is better and you don't need to serialize anything

public enum ExecutionMode {
  TYPE_A(x,t),
  TYPE_B(y,z),
  TYPE_C(b,s)

  private boolean incremental; //has get/set
  private String someStr;      //has get/set

  ExecutionMode(boolean incremental,String someStr){
        ///... set things appropriately
  } 
}

If you're setting these values at runtime, my inclination would be that this shouldn't be an enum in the first place - there should be a separate POJO that perhaps contains the values as well as a reference to an enum value.

Answer 2

From the Java language specification:

The final clone method in Enum ensures that enum constants can never be cloned, and the special treatment by the serialization mechanism ensures that duplicate instances are never created as a result of deserialization. Reflective instantiation of enum types is prohibited. Together, these four things ensure that no instances of an enum type exist beyond those defined by the enum constants.

What you are asking for would create more than one instance of, say, TYPE_A. This would break enums. Enums should be immutable.