One might think this is part of the class/interface preparation stage (JLS 12.3.2) which initializes things like method tables. So, it might be that there are both specification and HotSpot bugs here. Making statements based on opinion; back them up with references or personal experience. Find centralized, trusted content and collaborate around the technologies you use most. What is the difference between an interface and abstract class? Trending is based off of the highest score sort and falls back to it if no posts are trending. I'll try to make a case that an interface initialization should not cause any side-channel side effects that the subtypes depend on, therefore, whether this is a bug or not, or whichever way the Java fixes it, it should not matter to the application in which order interfaces are initialized. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. When is an interface with a default method initialized? initialized, but interfaces implemented by the class are not This approach is not time efficient as were initially creating an array, converting it to a list, and passing that list to create a set. I don't think it gets more official than this. initialized. ), I can not find JLS for Default methods, there may be two possibilities. What drives the appeal and nostalgia of Margaret Thatcher within UK Conservative Party? As per Javadoc, the set instances created by Set.of() have the following characteristics: If we need a set that can expand or shrink, we can use: Please note that unlike static methods on classes, static methods on interfaces are not inherited, so it will not be possible to invoke them via an implementing class nor an instance of the interface type. where the respective step has been included in the implementation: It is known at compile time that constant field of interface is not used anywhere, and the interface is not containing any default method (In java-8) so there is no need to initialize or load the interface. But perhaps this went too far and accidentally did full initialization instead. . . Announcing the Stacks Editor Beta release! I asked for official sources. @KishanSarsechaGajjar: What do you mean by non constant field in interface? Grep excluding line that ends in 0, but not 10, 100 etc. This creates an anonymous inner class with just an instance initializer in it. I'd say it's missing. Unfortunately, the order of superinterfaces are not supposed to be significant, therefore there is no well defined order in which to initialize them. In case of Default Methods, You are implementing InterfaceType. I am not giving the default method example as you already given that in your question. Why is "final" not allowed in Java 8 interface methods? How can I use parentheses when there are math parentheses inside? Enter your email address to subscribe to new posts. Therefore if we follow that principle, it'll be no concern to us in which order interfaces are initialized. 465), Design patterns for asynchronous API communication. We are sorry that this post was not useful for you!

Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. This indicates that this implementation followed some specification, but it seems that the written specification on the website has not been updated accordingly. I feel like your answer is just repeating things I've already stated in the question, ie. Any subclass of Foo would expect that they'll see $1000 in the bank, anywhere in the subclass code. They reject duplicate elements at creation time. I could not find anything in the JLS to indicate that this should happen. When elements are specified individually, this method provides a convenient way to add a few elements to an existing collection: Alternatively, one can populate a collection using a copy constructor from another collection. So we better not establish this kind of side effects in interface initializations. The example as follows: and indeed I get the expected output. It contains a new step that is not mentioned in the JLS and not in the JVM book that is referred to in the code: So this initialization has been implemented explicitly as a new Step 7.5. The set will throw an UnsupportedOperationException if any modification operation is performed on it. Asking for help, clarification, or responding to other answers. You can now choose to sort by Trending, which boosts votes that have happened recently, helping to surface more up-to-date answers. In above case, Interface will be initialized and loaded because you are using the field InterfaceType.init. (Specification Doc bug. I wrote this as a comment as I'm not sure whether this is correct statement :). bpel processes integrate interface user webservice endpoint defined wsdl process proxy create Similarly, the superinterfaces of an interface are not However, the behavior of Oracle JDK and OpenJDK (javac and HotSpot) differs from what's specified here. Unfortunately, that's what I am looking for. java initialize list arraylist declare values arrays length fixed linkedlist array create aslist example visit static Set of() How should I have explained the difference between an Interface and an Abstract class? Why does the capacitance value of an MLCC (capacitor) increase after heating? The specification doesnt guarantee the type of set returned by toSet(). Before a class is initialized, its direct superclass must be By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy.

If people think this gives me an unfair advantage at getting the bounty attached to this question, I'm willing to be flexible about it. Don't get me wrong, I understand that this should happen in case the implementing class doesn't provide an implementation for the method, but what if it does? Factories are free to create new instances or reuse existing ones. Is there a PRNG that visits every number exactly once, in a non-trivial bitspace, without repetition, without large memory usage, before it cycles? The mere presence of the default method is enough to trigger the initialization. The Interleaving Effect: How widely is this used? static Set of(E e1, E e2) There's been a reply from Alex Buckley (editor of the JLS) in which he raises more questions directed at the JVM and lambda implementation teams. Tannakian-type reconstruction of etale fundamental group. Any attempts to modify the returned set will result in an UnsupportedOperationException. web services domain xml programming definition name supposedly thing never again fun ll rpc promote english debian dictionary professional To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Reference: JEP 269: Convenience Factory Methods for Collections. For example, creating a set containing n elements involves constructing it, storing it in a variable, invoking the add() method on it n times, and then maybe wrapping it to make it unmodifiable: This post will discuss various methods to initialize a set in a single expression. Please note that duplicate elements will be rejected. No votes so far! This is because every invocation of a varargs method will cause an array allocation and initialization and, not to forget, GC overhead. The interface is not initialized because the constant field InterfaceType.init , which is being initialized by non constant value (method call), is not used anywhere. The field was just to demonstrate that the interface was initialized or not. Connect and share knowledge within a single location that is structured and easy to search. For example. How did this note help previous owner of this old film camera? Is this condition missing from the Java Language Specification, did I miss something, or am I interpreting it wrongly? One such method is Collections.unmodifiableSet() returns an unmodifiable view of the specified set. Apache Commons Collections SetUtils class provides unmodifiableSet() that returns an unmodifiable set backed by the given set. EDIT2: Coincidentally, I found this Document about default methods in hotspot which contains an interesting side note at the end: Because interfaces now have bytecode in them, we must initialize them at the Why did the gate before Minas Tirith break so very easily? They, along with the 14 upvotes (as of this writing) on assylias' comment, have alleviated my concerns about any potential unfairness. Shouldn't we do the same thing for superintefaces as well? It seems like JLS section 12.4.1 ought to cover this definitively. Explicitly calling a default method in Java, When to use: Java 8+ interface default method, vs. abstract method. Should I remove older low level jobs/education from my CV at this point? This creates a new class that inherits from HashSet. However, if the interface declares a default method, then initialization does occur. @SotiriosDelimanolis There are a couple bugs that seem relevant. It throws a NullPointerException if the given set is null and an UnsupportedOperationException if any modification operation is performed on it. In particular, the Example 12.4.1-3 from this section covers interface initialization. Another alternative is to use Double Brace Initialization. This may cause memory leaks or problems with serialization. static Set of(E e1)1 After all, interface is not meant for these features (static fields/methods) we pile on for convenience. (But mentioned no where, again Specification Doc bug.). My speculation is that the HotSpot implementation wanted to avoid adding class/interface initialization checking into the critical path of the invokevirtual call. This means that the interface was initialized. The var-args version is likely to run slower than the overloadings that do not use varargs.

They are structurally immutable. They are value-based. We can initialize a set by using HashSet constructor that can accept another collection, as shown below: Any duplicate elements present in the list will be rejected. He also notes that there's a bug in the spec here where it says "T is a class and a static method declared by T is invoked" should also apply if T is an interface. Java Interface Implementation - Automatic Initializer. Prior to Java 8 and default methods, invokevirtual could never end up executing code in an interface, so this didn't arise. @SotiriosDelimanolis I mentioned the reason in answer for Default methodbut unfortunately any JLS not found for default method yet. I'm looking for a reference for the default method. Interface with default method Initialisation, Java order of Initialization and Instantiation, Java interface static variable is not initialized, java.lang.NoSuchMethodError: VarHandle.compareAndSet(VariableHandlesExample,State,State)void, Force static part of class to run without instantiation. initialized before the interface is initialized. To learn more, see our tips on writing great answers. . It should be in section 12.4 of the JLS, but does not appear to be there. But, If you are accessing constant field of interface (which is initialized in normal way), The interface initialization is not required. Collectors.toSet() returns a Collector that accumulates the input elements into a new Set. The Collections class consists of several static methods that operate on collections and return a new collection backed by a specified collection.
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