Assuming that I have got completely different classes with different class names. Should I use different serialVersionUID in the classes?
If so, why is it necessary?
How does the JRE the deserialization exactly?
no you don't need different SUID (all classes can use 1 for it)
when an object is serialized the class identifier (package.name.ClassName) and SUID are both part of the header to identify the class the object belongs to and to ensure that there is no incompatibility between the writing side and the reading side
but when you change a class structurally (add/remove a field) you should set a new SUID for that class (during debugging you can let the JVM create a new one at runtime based on the .class file)
Related
ByteBuddy has net.bytebuddy.jar.asm.commons.Remapper which allows e.g. runtime shading by using a classloader which transforms and remaps classes during loading. But I have a problem with remapping type references in ByteBuddy Advice classes. I assume it happens because BB does not actually load them as classes, but merely uses getResourceAsStream or similar to get byte array of the Advice class files.
So, question: how can I supply a Remapper for Advice classes?
You think about locating advice classes? You can supply an optional argument of type ClassFileLocator which is responsible for finding a class file for a given class. You'd need to look up a .class file with a different name or write a delegator that adjusts the class name before passing on to a different class file locator.
Official docs on visibility modifiers in Kotlin say that package-level elements marked private are be visible only in the module in which they are declared.
So class A declared in Module1.kt isn't visible in Module2.kt. But if I try to add to Module2.kt it's own class A I get the Redeclaration: A error.
Since I can't access in Module2.kt to Module1's A class, why isn't the name A free to use?
"A module is a set of Kotlin files compiled together" (Visibility Modifiers - Kotlin Programming Language).
In your example, Module1.kt and Module2.kt are separate source files and despite their names they are not necessarily part of separate modules:
If they are compiled together then they are part of the same module.
If they are compiled separately from one another then they will be part of different modules and each can define their own private class A.
Keep in mind that visibility is different from identity. Even if a class is not visible elsewhere it doesn't mean that it does not exist. Loading multiple class declarations with the same fully-qualified name can (and likely will) cause issues at run-time.
How does JVM loads class that are defined inside another class?
Example: Lets say, there is a class B that is defined inside class A
package test.sample;
Class A {
// some instructions
Class B {
// few more instructions
}
}
In this case,
How does classloader load the class B? (i.e., How does it identify class B?)
What will be the fully qualified name of class B?
Inner classes are a Java language feature, not a JVM feature. That is, Java compilers "flatten" the class structure, so the JVM just sees regular classes, usually with $ in their names. In this case, there would be classes test.sample.A and test.sample.A$B (the latter being the fully qualified name of B). Anonymous inner classes get compiler-defined names, typically starting at 1 and counting up: test.sample.A$6, for example. The compiler may add methods with names like access$200 to allow the enclosing class and inner class to access each others' private members. (Note that $ is legal, though discouraged, in user-defined class and method names, so the presence of a $ in a name does not mean it is compiler-generated; for that, there's the Synthetic attribute and ACC_SYNTHETIC modifier bit, exposed reflectively via methods like Class.isSynthetic().)
The JVM loads these classes just like any other class, typically looking for a file test/sample/A$B.class in some JAR file, but also possibly loading them across a network, generating them on-the-fly with a bytecode manipulation library, etc.
When generating class files that reference an inner class (defining, containing, or simply using), Java compilers emit InnerClasses attributes specifying the containment relationships, for the aid of separate compilation and reflection (Class.getDeclaringClass() and Class.getEnclosingClass()). Class files for classes defined inside a method also contain an EnclosingMethod attribute referring to the enclosing method, for reflection (Class.getEnclosingMethod() and Class.getEnclosingConstructor()). However, these attributes are only checked for syntactic well-formedness by the JVM during loading and linking; inconsistencies are not reported until the reflective methods are actually called.
I have two frameworks in my Xcode project that both define a class with the same name (B.framework and C.framework both have a class named MyClass), resulting in a couple warnings like so:
Duplicate symbol _OBJC_METACLASS_$_MyClass originally in B.framework/B(MyClass.o) now lazily loaded from C.framework/C(MyClass.o)
Duplicate symbol _OBJC_CLASS_$_MyClass originally in B.framework/B(MyClass.o) now lazily loaded from C.framework/C(MyClass.o)
Then at run time only one of the implementations is loaded, and trying to use the other one will result in a "unrecognized selector sent to instance" because they are totally different classes (even though they have the same name).
I use one of the MyClass implementations directly in my code, but the other framework only uses its MyClass internally and I have no idea why its even exported (its not even mentioned in the frameworks header files, i used nm to view the symbols).
How can I make both frameworks work?
There's no such thing as "exported" classes in Obj-C. Or rather, there's no such thing as "non-exported" classes. This problem is precisely why the use of 2- or 3-letter prefixes on classes is strongly recommended for all Obj-C code. Your only solution (besides not using these frameworks) is to edit one (or both) of the frameworks to change the class name, or if you don't have access to the source, then you need to contact the vendor and ask them to make that change.
So we have a java class with two ArrayLists of generics. It looks like
public class Blah
{
public ArrayList<ConcreteClass> a;
public ArrayList<BaseClass> b;
}
by using [ArrayElementType('ConcreteClass')] in the actionscript class, we are able to get all the "a"s converted fine. However with "b", since the actual class coming across the line is a heterogeneous mix of classes like BaseClassImplementation1, BaseClassImplementation2 etc, it gets typed as an object. Is there a way to convert it to the specific concrete class assuming that a strongly typed AS version of the java class exists on the client side
thanks for your help!
Regis
To ensure that all of your DTO classes are marshalled across AS and Java, you need to define each remote class as a "remote class" in AS by using the "RemoteClass" attribute pointing to the java class definition like this [RemoteClass(alias="com.myco.class")].
BlazeDS will perform introspection on the class as it is being serialized/de-serialized and convert it appropriately (see doc below). It doesn't matter how the classes are packed or nested in an array, as long as it can be introspected it should work.
If you need special serialization for a class you can create your own serialization proxys (called beanproxy) by extending "AbastractProxy" and loading them into blazeds using the PropertyProxyRegistry register method on startup.
You will find most of this in the Blaze developers guide http://livedocs.adobe.com/blazeds/1/blazeds_devguide/.
Creating your own beanproxy class look here: //livedocs.adobe.com/blazeds/1/javadoc/flex/messaging/io/BeanProxy.html