Java enum and nested classes

Question

I'm a beginner with Java (Objective-C is my most well known language) and I'm really struggling to locate a clean example of what I'm trying to achieve:

public class OuterClass extends ClassToExtend {

    public enum Enum { value1, value2 }

    public class InnerClass extends AnotherClassToExtend {

        public void aMethod(int position) {
            switch (position) {
                case Enum.value1:
                    //Do something
                case Enum.value2:
                    //Do Something else
            }
        }
    }
}

Obviously this does not work (the references to the enum) but should give an idea of what I am trying to do, what needs changing to make this work? I think I need to declare the enum somewhere to reference it?

I would be grateful for an explanation of the corrections so that I can learn and hopefully solve similar difficulties for myself in the future.

Thanks

EDIT: What if the method was an @Override and the signature could not be changed?

FOA change type of position argument from int to Enum, since you've defined it, you should use it. For the switch just use case value1: and case value2. — BigMike
– BigMike, Commented Apr 4, 2013 at 15:02

Perception · Accepted Answer · 2013-04-04 15:19:32Z

3

Firstly, you must switch on the enum itself, so you need to change the following line:

public void aMethod(int position) {

To accept your enum instead of an int. Secondly, the values of the enum need to be referenced directly within the switch, as the enum is already in the scope of the current object.

public class OuterClass extends ClassToExtend {

    public enum Enum { value1, value2 };

    public class InnerClass extends AnotherClassToExtend {

        public void aMethod(Enum position) {
            switch (position) {
                case value1:
                    //Do something
                case value2:
                    //Do Something else
            }
        }
    }
}

edited Apr 4, 2013 at 15:19

Perception

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answered Apr 4, 2013 at 15:05

David

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4 Comments

BigMike Over a year ago

exact duplicate while posting an answer ^^ first time actually I see this kind of thing here on SO! +1 since is the very same answer I was typing

BigMike Over a year ago

@david99world I mean I got an "exact duplicate answer" while posting my answer (so I decide not to post it and +1 yours ^^)

David Over a year ago

Ah my apologies, I thought you meant it was the same as the current answer.

amcc Over a year ago

Thanks, I will mark this as correct since it explains the main reason as to why my implementation fails. (Enum and int are not interchangeable)

NimChimpsky · Accepted Answer · 2013-04-04 15:24:25Z

2

override from an abstract class requiring the method with the int paramater

I would do this :

public enum Enum { value1, value2 }
public class InnerClass  {
  public void aMethod(int position) {
    Enum value = Enum.values()[position];
    switch (value) {
      case value1:

edited Apr 4, 2013 at 15:24

answered Apr 4, 2013 at 15:06

NimChimpsky

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2 Comments

amcc Over a year ago

If the method was an override from an abstract class requiring the method with the int paramater, would this be the preferable solution?

amcc Over a year ago

Thank you, this actually solves my specific issue but due to the way I phrased my question the accepted answer is probably the more acceptable.

Uwe Plonus · Accepted Answer · 2013-04-05 06:02:19Z

2

You cannot switch on an int and then try to match this with an enum.

If you change you method signature to

public void aMethod(Enum position)

and use the bare enum values (e.g. value1) then it should work:

case value1:

edited Apr 5, 2013 at 6:02

answered Apr 4, 2013 at 15:03

Uwe Plonus

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Comments

Waqas Memon · Accepted Answer · 2013-04-04 15:38:03Z

0

your aMethod should not use int as argument type. Prior to JDK6, it was also not possible to use Strings in Switch Statement. Switch statements with String cases have been implemented in Java SE 7, at least 16 years after they were first requested.

You should also not forget break statements after each case. Otherwise, all your cases will be read.

public void aMethod(Enum position) {
 switch (position) {
                case value1:
                    System.out.println("I am Value 1");
                    break;
                case value2:
                    System.out.println("I am Value 1");
                    break;
 }
}

to test it, use

ob.aMethod(Enum.value1);

or

ob.aMethod(Enum.valueOf("value1"));

answered Apr 4, 2013 at 15:38

Waqas Memon

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1 Comment

amcc Over a year ago

My intention was not to use strings as the cases but rather for value1 of the enum to reference the integer for the index at which it was stated, ie value1 = int 0 etc

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