Using a method to create enum values

Question

I have an enum: public enum X implements Y

I also have a class Ybuilder which can create instances of Y, let's say with Ybuilder.create(int value)

How can I set the enum values in my enum to be instances of Y created with Ybuilder? ideally it would be something simple like

public enum X implements Y {
  A (Ybuilder.create(0)),
  B (Ybuilder.create(1)),
};

X should have a constructor that takes Y as parameter type — Ramanlfc
– Ramanlfc, Commented Feb 29, 2016 at 18:40
depends on what you want , you can have instance members of type T that you can set — Ramanlfc
– Ramanlfc, Commented Feb 29, 2016 at 18:41

assylias · Accepted Answer · 2016-02-29 18:50:13Z

6

I don't think you can do it that way - one alternative would be to delegate to the Y instance created by the builder. For example:

interface Y { //Assume Y has two methods
   void m1();
   void m2();
}

public enum X implements Y {
  A (0),
  B (1);
  private final Y y;
  X(int value) { this.y = YBuilder.create(value); }

  //Then delegate to y to implement the Y interface

  public void m1() { y.m1(); return; }
  public void m2() { y.m2(); return; }
};

Note that I created the enums with the int argument but you can pass a Y directly if you prefer:

public enum X implements Y {
  A (Ybuilder.create(0)),
  B (Ybuilder.create(1));
  private final Y y;
  X(Y y) { this.y = y; }
};

edited Feb 29, 2016 at 18:50

answered Feb 29, 2016 at 18:41

assylias

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3 Comments

Andrew Latham Over a year ago

Is there a way to not have to implement all of Y's methods? Y actually has a lot of methods and it's annoying for this enum to have a bunch of methods that just return y.method();

Louis Wasserman Over a year ago

@AndrewLatham it looks a lot like enums aren't necessarily right for this use case; that you actually just want a bunch of constants.

Holger Over a year ago

Of course, there is a way not to have to implement all of Y's methods. Just don’t let X implement Y. Just add one method to X to get the Y instance and you’re done.

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