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. For example, we could adapt the toSet() collector to always produce an unmodifiable set with: Java 9 made it convenient to create instances of a list with small numbers of elements by providing Sets.of() static factory methods that create compact, unmodifiable instances. I feel like your answer is just repeating things I've already stated in the question, ie. When adding a new disk to RAID 1, why does it sync unused space? I could not find anything in the JLS to indicate that this should happen. Unfortunately, the order of superinterfaces are not supposed to be significant, therefore there is no well defined order in which to initialize them. And Initialization will be into the picture. Give it two days to see all developments. How did this note help previous owner of this old film camera? Elements to be added may be specified individually or as an array. Collectors.toSet() returns a Collector that accumulates the input elements into a new Set. Please note that duplicate elements will be rejected. We can use toCollection() to ensure that the returned type of Set is HashSet, as shown below: We could adapt a collector to perform an additional finishing transformation. How should I have explained the difference between an Interface and an Abstract class? The default method doesn't have to be called or overridden or even mentioned, nor does the presence of an abstract method trigger initialization. E e8, E e9) Attempts to create them with null elements result in. What is the difference between an interface and abstract class? Enter your email address to subscribe to new posts. where the respective step has been included in the implementation: http://hg.openjdk.java.net/jdk8/build/hotspot/rev/4735d2c84362. Nevermind.most of the time when they don't understand or do not have an explanation they will downvote :( .This happens on SO generally. Why had climate change not been proven beyond doubt for so long? Connect and share knowledge within a single location that is structured and easy to search. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. 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. Refer to the following post for details: Thats all about initializing Set in Java. Elements cannot be added, removed, or replaced. The obvious question is why Java 9 has included so many extra methods when only var-args can suffice? This means that the interface was initialized. Any attempts to modify the returned set will result in an UnsupportedOperationException. 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. Therefore, identity-sensitive operations on these instances (reference equality (==), identity hash code, and synchronization) are unreliable and should be avoided. Reference: JEP 269: Convenience Factory Methods for Collections. Asking for help, clarification, or responding to other answers. This is because every invocation of a varargs method will cause an array allocation and initialization and, not to forget, GC overhead. I've raised this question on the OpenJDK compiler-dev mailing list. bash loop to replace middle of string after a certain character. A side note: The JVM Spec contains a description that is similar to that of the JLS: @assylias and Sotirios, thanks for your comments. that an interface will be initialized if it contains a. I think java people forgot to consider the case of default method, Or they just refer the default methods as non-constant member of interface(my assumption, can not find in any doc). 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. static Set of(E elements). Interface contains a default method (Java 8), Java people forgot to consider the case of default method. Why does the capacitance value of an MLCC (capacitor) increase after heating? Why did the gate before Minas Tirith break so very easily? @SotiriosDelimanolis There are a couple bugs that seem relevant. One might think this is part of the class/interface preparation stage (JLS 12.3.2) which initializes things like method tables. The example as follows: and indeed I get the expected output. initialized. So, it might be that there are both specification and HotSpot bugs here. . interface. Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, My guess would be - such interfaces considered abstract classes in terms of initialization order. Explicitly calling a default method in Java, When to use: Java 8+ interface default method, vs. abstract method. ), They just refer the default methods as non-constant member of They are structurally immutable. My speculation is that the HotSpot implementation wanted to avoid adding class/interface initialization checking into the critical path of the invokevirtual call. In the case of a class, it is well accepted that it can cause side effects that subclasses depend on. This creates an anonymous inner class with just an instance initializer in it. Thanks for digging this up. We can use the Java 8 Stream to construct small sets by obtaining stream from static factory methods and accumulating the input elements into a new set using collectors. Before a class is initialized, its direct superclass must be (Specification Doc bug. I'd say it's missing. initialized before the interface is initialized. The field was just to demonstrate that the interface was initialized or not. static Set of(E e1, E e2, E e3, E e4, . However, if a default method is added to interface I. which clearly indicates that interface I is being initialized where it wasn't before! I asked for official sources. Is there a PRNG that visits every number exactly once, in a non-trivial bitspace, without repetition, without large memory usage, before it cycles? (But mentioned no where, again Specification Doc bug.). The set will throw an UnsupportedOperationException if any modification operation is performed on it. Java 9 provides 12 overloaded versions of this method with one varargs method, which can handle any number of elements. One such method is Collections.unmodifiableSet() returns an unmodifiable view of the specified set. (+1) It may be that the new "step 7.5" was inadvertently omitted from the spec, or that it was proposed and rejected and the implementation never was fixed up to remove it. After all, interface is not meant for these features (static fields/methods) we pile on for convenience. . Even though Java 8 and above returns a HashSet, this might change in future releases. To learn more, see our tips on writing great answers. You can now choose to sort by Trending, which boosts votes that have happened recently, helping to surface more up-to-date answers. This indicates that this implementation followed some specification, but it seems that the written specification on the website has not been updated accordingly. . Thanks for contributing an answer to Stack Overflow! step 9 in the Detailed Initialization Procedure, docs.oracle.com/javase/specs/jvms/se8/html/jvms-5.html#jvms-5.5, http://hg.openjdk.java.net/jdk8/build/hotspot/rev/4735d2c84362, Document about default methods in hotspot, How APIs can take the pain out of legacy system headaches (Ep. 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. So, If InterfaceType will contain any default methods, It will be INHERITED (used) in implementing class. I am not giving the default method example as you already given that in your question. Trending is based off of the highest score sort and falls back to it if no posts are trending. time that an implementing class is initialized. @SotiriosDelimanolis I mentioned the reason in answer for Default methodbut unfortunately any JLS not found for default method yet. Another alternative is to use Double Brace Initialization. In other words, the static field of the interface is initialized (step 9 in the Detailed Initialization Procedure) and the static initializer of the type being initialized is executed. So we better not establish this kind of side effects in interface initializations. When to use LinkedList over ArrayList in Java? static Set of(E e1, E e2) Similarly, the superinterfaces of an interface are not Using spring managed beans in an interface default method? The reason is theres a subtle runtime performance advantage. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. 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. For example. Interface will be initialized in following cases. We should avoid this approach as it costs an extra class at each usage. Should I remove older low level jobs/education from my CV at this point? No votes so far! 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. Apache Commons Collections SetUtils class provides unmodifiableSet() that returns an unmodifiable set backed by the given set. 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. What drives the appeal and nostalgia of Margaret Thatcher within UK Conservative Party? 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. Is there a way to generate energy using a planet's angular momentum. I wrote this as a comment as I'm not sure whether this is correct statement :). 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. rev2022.7.21.42639. 465), Design patterns for asynchronous API communication. Java language specification and example is given in JLS 12.4.1 (Example does not contain default methods. Prior to Java 8 and default methods, invokevirtual could never end up executing code in an interface, so this didn't arise. The specification doesnt guarantee the type of set returned by toSet(). Consider the InterfaceType interface given as. 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 The instanceKlass.cpp file from the OpenJDK contains the initialization method InstanceKlass::initialize_impl that corresponds to the Detailed Initialization Procedure in the JLS, which is analogously found in the Initialization section in the JVM Spec. Making statements based on opinion; back them up with references or personal experience. It seems like JLS section 12.4.1 ought to cover this definitively. For example. We are sorry that this post was not useful for you! Sets with both additive and multiplicative gaps. The var-args version is likely to run slower than the overloadings that do not use varargs. Java Interface Implementation - Automatic Initializer. This may cause memory leaks or problems with serialization. It also holds hidden references to the enclosing instance and any captured objects. They reject duplicate elements at creation time. Therefore the superclass is initialized prior to the subclass. However, if the interface declares a default method, then initialization does occur. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. The Interleaving Effect: How widely is this used? In particular, the Example 12.4.1-3 from this section covers interface initialization. ), I can not find JLS for Default methods, there may be two possibilities. static Set of(E e1)1 Calling any mutator method will always cause, They disallow null elements. 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. The Collections class consists of several static methods that operate on collections and return a new collection backed by a specified collection. Is this condition missing from the Java Language Specification, did I miss something, or am I interpreting it wrongly? @KishanSarsechaGajjar: What do you mean by non constant field in interface? Java is often criticized for its verbosity. Announcing the Stacks Editor Beta release! 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. . For my own curiosity, I tried it and, as expected, the interface InterfaceType was not initialized. 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? In above case, Interface will be initialized and loaded because you are using the field InterfaceType.init. I'm looking for a reference for the default method. I don't think it gets more official than this. Callers should make no assumptions about the identity of the returned instances. initialized, but interfaces implemented by the class are not For example. Therefore if we follow that principle, it'll be no concern to us in which order interfaces are initialized. static Set of() Duplicate elements passed to a static factory method result in. While searching through the Java Language Specification to answer this question, I learned that. They, along with the 14 upvotes (as of this writing) on assylias' comment, have alleviated my concerns about any potential unfairness. The mere presence of the default method is enough to trigger the initialization. Grep excluding line that ends in 0, but not 10, 100 etc. But, If you are accessing constant field of interface (which is initialized in normal way), The interface initialization is not required. Can a timeseries with a clear trend be considered stationary? Shouldn't we do the same thing for superintefaces as well? When is an interface with a default method initialized? Be the first to rate this post. Factories are free to create new instances or reuse existing ones. 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. This creates a new class that inherits from HashSet. They are serializable if all elements are serializable. In case of Default Methods, You are implementing InterfaceType. EDIT: As a reference, the commit (from October 2012!) Unfortunately, that's what I am looking for. It throws a NullPointerException if the given set is null and an UnsupportedOperationException if any modification operation is performed on it. Any subclass of Foo would expect that they'll see $1000 in the bank, anywhere in the subclass code. They are value-based. Do NOT follow this link or you will be banned from the site! Find centralized, trusted content and collaborate around the technologies you use most. Any variable/field in interface is static final by default. static Set of(E e1, E e2, E e3, E e4, . Collections also have an unmodifiableSortedSet(SortedSet s) method that returns an unmodifiable view of the specified sorted set. Java8: Why is it forbidden to define a default method for a method from java.lang.Object. The order of elements in the list is the same as the order of the provided arguments or of the elements in the provided array. Collections.addAll() adds all the specified elements to the specified collection. Disclosure: I work for Oracle on OpenJDK. Does Java support default parameter values? However, the behavior of Oracle JDK and OpenJDK (javac and HotSpot) differs from what's specified here. But perhaps this went too far and accidentally did full initialization instead. Guava also provides several static utility methods pertaining to set instances. Why is "final" not allowed in Java 8 interface methods? Tannakian-type reconstruction of etale fundamental group. JEP 269: Convenience Factory Methods for Collections. Why can't I define a static method in a Java interface? This post will discuss various methods to initialize a set in Java in a single line. If we want a set containing only a single element, we can use Collections.singleton() that returns an immutable set containing that element. E e8, E e9, E e10) How can I use parentheses when there are math parentheses inside? It should be in section 12.4 of the JLS, but does not appear to be there.