Is it possible to override methods in enum

It only takes a minute to sign up. Connect and share knowledge within a single location that is structured and easy to search. I am managing the changing of views in an Android app using this enum and associated methods. I am particularly interested in the Page enum's use of overriding previous and next for the first and last elements. Interesting question. Overriding methods in enum instances is not something I have encountered that I recall.

This is not to say it's a bad thing, just not very common. The concept is something I have solved using different mechanisms before, but I can understand why having the override makes sense to you. What I don't understand is why you did not just use a regular bound-clipping system. Why do you need the overrides at all? On the other hand, if you do override them, then please use a standard indentation for the override methods.

Cramming it all on one line is not helpful:. As far as the enum is concerned, the solution seems fine. Even clever, but still very readable, so that's not a problem.

Using ordinal is usually not recommended, but in this case I think it's justified. An alternative dates structure would be an ADT abstract data type representing the page transition actions, implemented as a regular class, with the same methods that you implemented in the enum. In principle, creating an ADT would be the right thing to do, but if you don't anticipate further evolution of managing your page transitions, then your simple solution is fine. If later you find yourself wanting to add any more logic to the enum, that will be a good time to ditch the enum.

If Page is an inner class, then it should be a public static enum , because it doesn't rely on anything in the enclosing class. The only way to test is write if page. This is not to say it's a bad thing, just not very common. Even clever, but still very readable, so that's not a problem. Using ordinal is usually not recommended, but in this case I think it's justified. By default, the enum value is its method name.

You can however override it, for example if you want to store enums as integers in a database, instead of using their method name. Check your current version with the following command:. This method may be overridden, though it typically isn't necessary or desirable. An enum type should override this method when a more "programmer-friendly" string form exists. Overrides: toString in class Object Returns: the name of this enum constant , Note that when using an enumeration type as the type of a set or as the type of the keys in a map, specialized and efficient set and map implementations are available.

All the constants of an enum type can be obtained by calling the implicit public static T[] values method of that type. Most programmers should use the toString method in preference to this one, as the toString method may return a more user-friendly name.

This method is designed primarily for use in specialized situations where correctness depends on getting the exact name, which will not vary from release to release. Returns: the name of this enum constant.

You can always move the method inside the enum and have it constructed like this:. Enum class, which returns enum constant name. The enum valueOf method helps to convert string to enum instance. We should use enum when we know all possible values of a variable at compile time or design time, though we can add more values in future as and when we identify them. In this java enum tutorial , we will learn what enums are and what problems they solve? A simple example to create enum.

As we know, generally we deal with four directions in daily life. Their names, angles and other properties are fixed. So, in programs, we can create enum for them. Syntax to create an enum is as below:. Logically, each enum is an instance of enum type itself. So given enum can be seen as below declaration. JVM internally adds ordinal and value methods to this class which we can call while working with enum.

Note that in Python 3. Enums are advantageous because they give a name to a constant, which makes code more readable; and because the individual members cannot be rebound, making Python Enums semi-constant because the Enum itself could still be rebound.

Besides more readable code, debugging is also easier as you see a name along with the value, not just the value. For example, as anyone who has worked with the datetime module knows, datetime and date have two different representations for the days of the week: or Rather than keep track of that ourselves we can add a method to the Weekday enum to extract the day from the datetime or date instance and return the matching enum member:.

Enum is a type, whose members are named constants, that all belong to or should a logical group of values. So far I have created Enum s for:. FederalHoliday is my most complex; it uses this recipe, and has methods to return the actual date the holiday takes place on for the year given, the next business day if the day in question is a holiday or the range of days skipped includes the holiday or weekends , and the complete set of dates for a year.

Here it is:. Disclosure: I am the author of the Python stdlib Enum , the enum34 backport, and the Advanced Enumeration aenum library. As described in python documentation, when python see some import statement it does the following things:. Put above files to the same directory.

When module. When you launch main. So import really happens only once. You can adjust this toy example to check cases that are interesting to you. I started my analysis disassembling the enum Color using javap -c. Here is an excerpt from:. The line ReflectEnum. This enum constant was not set to null.

So it broke the valueOf method of Color completely. But Enum. Since the enum array is declared as static final I followed Change private static final field using Java reflection to create and set a new enum array. But executing setEnumsArray Color. BLUE, Color. RED, Color. BLUE fails with. Then it should be possible to replace an enum singleton instance by another one. I have the following enum singleton:.