Closed issue: Should reabstraction be permitted? The LDM notes say that reabstraction is permitted in an interface. Not in a class. We decided to allow modifiers explicitly stated on interface members, unless there is a reason to disallow some of them. This brings an interesting question around virtual modifier. Should it be required on members with default implementation? Alternatively, we could say that virtual modifier is required for a virtual member. This approach might provide better experience when a method is moved from a class to an interface:.
Closed Issue: Should a concrete method with implementation be implicitly virtual? We understand that the implementation of I1.
What if the assembly containing I2 is changed as follows and recompiled. What happens when the program is run? An invocation of C as I1. Decision: Made Runs I2. M , which is the unambiguously most specific override at runtime. This "partial" implementation of the event is not permitted because, as in a class, the syntax for an event declaration does not permit only one accessor; both or neither must be provided.
You could accomplish the same thing by permitting the abstract remove accessor in the syntax to be implicitly abstract by the absence of a body:. Note that this is a new proposed syntax. In the current grammar, event accessors have a mandatory body. Closed Issue: Can an event accessor be implicitly abstract by the omission of a body, similarly to the way that methods in interfaces and property accessors are implicitly abstract by the omission of a body?
Decision: No, event declarations require both concrete accessors or neither. Closed Issue: We should confirm that this is permitted otherwise adding a default implementation would be a breaking change :. Decision: Yes, adding a body to an interface member declaration shouldn't break C. The previous question implicitly assumes that the sealed modifier can be applied to an override in an interface. This contradicts the draft specification.
Do we want to permit sealing an override? Source and binary compatibility effects of sealing should be considered. Decision: Let's not allowed sealed on overrides in interfaces. The only use of sealed on interface members is to make them non-virtual in their initial declaration.
The draft of the proposal prefers class overrides to interface overrides in diamond inheritance scenarios:. We require that every interface and class have a most specific override for every interface method among the overrides appearing in the type or its direct and indirect interfaces. If there is no override, the method itself is considered the most specific override. Closed Issue: Confirm the draft spec, above, for most specific override as it applies to mixed classes and interfaces a class takes priority over an interface.
Boxing in this way defeats the principal benefits of a struct type. Moreover, any mutation methods will have no apparent effect, because they are operating on a boxed copy of the struct:. Decision: Not worry about it and just leave it as a wart. The draft spec suggests a syntax for base interface invocations inspired by Java: Interface. We need to select a syntax, at least for the initial prototype. Decision: The syntax is base Interface.
The interface so named must be a base interface, but does not need to be a direct base interface. Open Issue: Should base interface invocations be permitted in class members? In an interface, non-public members from base interfaces are overridden using the override modifier. If it is an "explicit" override that names the interface containing the member, the access modifier is omitted. Closed Issue: If it is an "implicit" override that does not name the interface, does the access modifier have to match?
Decision: Only public members may be implicitly overridden, and the access must match. Open Issue: Is the access modifier required, optional, or omitted on an explicit override such as override void IB. Open Issue: Is override required, optional, or omitted on an explicit override such as void IB.
How does one implement a non-public interface member in a class? Perhaps it must be done explicitly? Closed Issue: How does one implement a non-public interface member in a class? Decision: You can only implement non-public interface members explicitly. Decision : No override keyword permitted on interface members. What if the assembly containing I3 is changed as follows and recompiled.
Decision : Throw an exception 5. Given that interfaces may be used in ways analogous to the way abstract classes are used, it may be useful to declare them partial. This would be particularly useful in the face of generators. Proposal: Remove the language restriction that interfaces and members of interfaces may not be declared partial. Open Issue: Is a static Main method in an interface a candidate to be the program's entry point? Can we please confirm or reverse our decision to permit non-virtual public methods in an interface?
Semi-Closed Issue: We think it is going to be useful, but will come back to it. This is a mental model tripping block. Open Issue: Does an override declaration in an interface introduce a new member?
In a class, an overriding method is "visible" in some senses. For example, the names of its parameters take precedence over the names of parameters in the overridden method. It may be possible to duplicate that behavior in interfaces, as there is always a most specific override. But do we want to duplicate that behavior? Active 1 year, 2 months ago. Viewed 18k times. Is it just because of syntax or because of something more fundamental? OK it's implicit but why would it hurt to make it explicit?
Jeff Puckett A "class interface"? Add a comment. Active Oldest Votes. Bala R Bala R k 22 22 gold badges silver badges bronze badges. OK it's implicit but why would it hurt to make it explicit.
IMHO you should only have to specify something when there is an alternative. When there is no alternative, why specify it? This is one of the reasons I dislike VB. NET, keywords such as Function and Sub are so redundant and clutter my code adding nothing. The comment you quoted from StackOverflow is now outdated. Saying that adding the public modifier is bad writing since it implies it can be non-public is contradictory. The method can be non-public.
DavidCampbell: Well, I think this question might be better asked after Java 9 comes out. Now I am vindicated because Java 8 and 9 complicate things Java is plenty redundant already. It's information a developer should already be aware of, which is why it's inferred. The less useless information on the screen, the easier it is to process the important information.
Hopefully I've persuaded you to come to the dark side Get it? Cause implicit stuff can't be seen. If not, it was worth a shot haha. In the end, it comes down to what makes the code easier to manage for the developer — Dioxin. Vince, no, I wouldn't extend Object, though I don't throw a fit when I see code that does so.
JimmyJames, if one is consistent adding public abstract to items that are so, I don't see any confusion. Am I missing something? OTOH, I do see your point on clutter. For example, I don't add final before method arguments unless something funny requires it like an anonymous inner class etc I wouldn't throw a fit if I saw extends Object , but it would definitely raise a flag and make me question why.
As I mentioned in the post, doing such things could imply that the developer may have a misunderstanding of how something works may not know that all objects already extend Object , hence the explicit extension — Dioxin. Show 7 more comments. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password.
Let me first create a simple Java interface that contains a single method:. This interface represents an interface which contains a single method called produce which can produce a single object.
Since the return value of produce is Object , it can return any Java object. The above class CarProducer implements the MyProducer interface. The implementation of the produce method returns a new Car object every time it is called.
Here is how it looks to use the CarProducer class:. Notice how the object returned from the carProducer. Using Java Generics you can type the MyProducer interface so you can specify what type of object it produces when you use it. Here is first a generic version of the MyProducer interface:. Now when I implement the MyProducer interface in the CarProducer class, I have to include the generic type declaration too, like this:.
Now, when creating a CarProducer I can specify its generic interface type, like this:. As you can see, since the generic type for the CarProducer instance is set to Car , it is no longer necessary to cast the object returned from the produce method, since the original method declaration in the MyProducer interface states, that this method returns the same type as is specified in the generic type when used.
But - now it is actually possible to specify another generic type for a CarProducer instance than the type it actually returns from it's produce method implementation. If you scroll up, you can see that the CarProducer. So, the following declaration is possible, but would return in a ClassCastException when executed:. Instead, you can lock down the generic type of the MyProducer interface already when you implement it, in the CarProducer class.
Here is an example of specifying the generic type of a generic interface when implementing it:. Now you cannot specify the generic type of the CarProducer when using it. It is already typed to Car. Here is how using the CarProducer looks:. As you can see, it is still not necessary to cast the object returned by produce , as the CarProducer implementation declares that to be a Car instance. Java generics is covered in more detail in my Java Generics Tutorial.
From Java 8 a new concept was introduced called functional interfaces. In short, a functional interface is an interface with a single, unimplemented method non-default, non-static method. I have explained functional interfaces in my Java functional interface tutorial , which is part of my Java Functional Programming Tutorial. Functional interfaces are often intended to be implemented by a Java Lambda Expression. Tutorials About RSS. Java Language.
The variable can be accessed directly from the interface, like this: System. Implementing an Interface Before you can really use an interface, you must implement that interface in some Java class. Interface Instances Once a Java class implements an Java interface you can use an instance of that class as an instance of that interface.
For instance: import com. MyInterface; import com. Interface Default Methods Before Java 8 Java interfaces could not contain an implementation of the methods, but only contain the method signatures. Interface Static Methods A Java interface can have static methods. Here is an example of calling the static print method from the above MyInterface interface: MyInterface.
Interfaces and Inheritance It is possible for a Java interface to inherit from another Java interface, just like classes can inherit from other classes.
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