extending an abstract class with generic enum type

Question

Is there a way to extend an abstract class with generic enum types? When I extend it and implement myMethod below, only the method from the abstract class gets called.

first i define abstract class with method myMethod where i would like to make decisions based on the enum value.

public abstract class MyAbstractClass <T extends enum<T>> {

    public void myMethod(T cmd) {
      //i want to override this
    }

    public void update(T cmd) {
      myMethod(cmd);
    }
}

define an enum and extend the class, but the child class myMethod never gets called(only the myMethod of abstract class gets called).

enum CMD {
   CMD_1, CMD_2
}

public class Child extends MyAbstractClass<CMD> {
...
  public void myMethod(CMD cmd) {
    if (cmd == CMD_1) { //do something }
  }
...
}

instantiate and call

Child child = new Child();
child.update(CMD.CMD_1);

Possible duplicate of [Can I override a private method in Java?](http://stackoverflow.com/questions/10623913/can-i-override-a-private-method-in-java) — Philipp Wendler, Apr 29 '17 at 11:44
thx for the link..if i correct my code to make it public it still doesnt seem to work. — prostock, Apr 29 '17 at 11:48
Use the construction suggested by @Bohemian. With the method which override the base one declared protected or public it must work. — Ilya Patrikeev, Apr 29 '17 at 12:02
What is `enum`? Perhaps you meant `Enum`? Did you actually try to compile the code you posted? — Lew Bloch, Apr 29 '17 at 14:50

Bohemian · Accepted Answer · 2017-04-29T11:58:08.680

1

Yes. Use T extends Enum<T>:

public abstract class MyAbstractClass <T extends Enum<T>> {
    public void myMethod(T cmd) {}
}

See live demo of your code, with this change, compiling OK.

edited Apr 29 '17 at 11:58

answered Apr 29 '17 at 11:23

Bohemian

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thx for getting back, but my initial post wasn't too clear so i edited it. actually my issue is when i extend the abstract class and try to use CMD to make a decision on actions to perform. myMethod, which i override, never gets called. instead the parent implementation gets called. – prostock Apr 29 '17 at 11:41
1

@prostock the overridden method *does* get called. See updated link with demo code proving this. – Bohemian Apr 29 '17 at 11:59

score 0 · Answer 2 · answered Apr 29 '17 at 12:29

If you want to select the behaviour according to the enum value, then one way to do it is to put the behaviour into each enum value, e.g.:

enum Command {
    CMD1 {
        @Override
        void execute() {
            System.out.println("Command.CMD1");
        }
    },
    CMD2 {
        @Override
        void execute() {
            System.out.println("Command.CMD2");
        }
    };

    abstract void execute();
}

public static void main(String[] args) {
    final Command cmd = Command.CMD1;

    cmd.execute();
}

extending an abstract class with generic enum type

2 Answers2