![]() Javac -source 1.8 -target 1.8 CallDefaultMethodThroughReflection. It’s also available in this gist here.Ĭompile it with JDK 9 or 10 (because it also tries using JDK 9+ API: MethodHandles.privateLookupIn()), but compile it using this command, so you can also run the class on JDK 8: The following class tries all combinations. So far, I’ve just been trying to run different things on different JDKs. So, there’s a solution (hack) that works on Java 8 but not on 9 or 10, and there’s a solution that works on Java 9 and 10, but not on Java 8. Great, it works in Java 9 and 10, what about Java 8?Ĭaused by: : no private access for invokespecial: interface Duck, from ProxyDemoĪt $Lookup.findSpecial(MethodHandles.java:1002) One of the Jigsaw project’s goals is to precisely not allow such hacks to persist. If we run the program with the -illegal-access=deny flag:Įxception in thread "main" : Unable to make $Lookup() accessible: module java.base does not "opens " to unnamed module java.base/.checkCanSetAccessible(AccessibleObject.java:337)Īt java.base/.checkCanSetAccessible(AccessibleObject.java:281)Īt java.base/.checkCanSetAccessible(Constructor.java:192)Īt java.base/.setAccessible(Constructor.java:185) WARNING: All illegal access operations will be denied in a future release WARNING: Use -illegal-access=warn to enable warnings of further illegal reflective access operations WARNING: Please consider reporting this to the maintainers of ProxyDemo WARNING: Illegal reflective access by ProxyDemo (file:/C:/Users/lukas/workspace/playground/target/classes/) to constructor $Lookup() WARNING: An illegal reflective access operation has occurred When googling further, we might find the following solution, which accesses MethodHandles.Lookup‘s internals through reflection: Thit k interface luôn là mt công vic rt khó khn, bi vì khi chúng ta thay i các phng thc bên trong interface nó òi hi. Still this is a viable extreme standpoint but fruitless. Nhng trong Java 8 chúng ta s có thêm 2 khái nim mi i vi interface là phng thc default (default methods) và phng thc static (static methods). Now your colleague would have to argue that the JLS of Java 8 perverted interfaces and the JDK now contains classes which go against the purpose of interfaces. We get the following IllegalAccessException:Ĭaused by: : no private access for invokespecial: interface Duck, from Duck/packageĪt .makeAccessException(MemberName.java:850)Īt $Lookup.checkSpecialCaller(MethodHandles.java:1572)Īt $Lookup.unreflectSpecial(MethodHandles.java:1231)īummer. This argument was valid until default interface methods were introduced. The almost same code snippet no longer works. So, the original Google search turned up results that indicate we need to use the MethodHandles API. You simply cannot do this):Įxception in thread "main" Ĭaused by: Īt 0(Native Method)Īt (NativeMethodAccessorImpl.java:62)Īt (DelegatingMethodAccessorImpl.java:43)Īt .invoke(Method.java:498)Ĭaused by: Thread.currentThread().getContextClassLoader(),īut this will just generate a long long stack trace of nested exceptions (this isn’t specific to the method being a default method. So, we need to solve the conflicts ourselves.Duck duck = (Duck) Proxy.newProxyInstance( ![]() If there is not a unique winner according to the above rules, concrete classes must disambiguate manually. A default from List wins over a default from Collection, regardless of where or how or how many times List and Collection enter the inheritance graph. More specific interfaces win over less specific ones* (where specificity means "subtyping"). If a class in the superclass chain has a declaration for the method (concrete or abstract), you're done, and defaults are irrelevant. ![]() There are three rules to consider in the method lookup while dealing with default methods:Ĭlasses win over interfaces. Public default String m1() Īnd we have our multiple inheritance. How do we define a default method (whatever that is)? Now we can fully dive into Java Interface default methods. You have to handle conflicts by yourself. It’s like they were copied into the class. The methods defined in the trait «have the same semantics» as the method defined in the class (Flattening property). Traits: Allow us to define behaviour outside the class, but don't define state. Mixins automatically solves conflict by linearization (inserting the mixin in the method lookup chain from left to right). You can call super from inside the mixin, and can define both methods and variables. So, let's get on it.įirst of all, if you don’t know what I’m talking about, read my previous post -and please ignore the fact that it took me almost half a year to write this second part :) ![]() In my last post I've presented both traits and mixins, with the promise of identifying the Java 8 Interface Default Methods. ![]()
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