Question

So I have my enum

public enum Sample {
   ValueA{
      @Override
   public String getValue(){ return "A"; }   
 },
 ValueB{
    @Override
   public String getValue(){ return "B"; }

   public void doSomething(){ }
 };
abstract public String getValue();
};

and I have some other code trying to use the enum.

Sample.ValueB.doSomething();

Which seems like it should be valid, but produces the error “The method doSomething() is undefined for the type Sample”. As opposed to

Sample value = Sample.ValueB;
value.doSomething();

which produces the same error and seems reasonable.

I assume there is a reasonable answer as to why the first one doesn’t work and it relates to the two examples being equivalent under the hood. I was hoping someone could point me towards the documentation on why it is that way.

Answer 1

The type of the “field” ValueA is Sample. That means that you can only invoke methods on ValueA that Sample provides. From JLS §8.9.1. Enum Constants:

Instance methods declared in these class bodies may be invoked outside the enclosing enum type only if they override accessible methods in the enclosing enum type.

More importantly: From a design perspective enum values should be uniform: if some operation is possible with one specific value, then it should be possible with all values (although it might result in different code being executed).