bytecode

Motivation I have a SomeObject.java file: class SomeObject { String name; } Compiling it creates a bytecode-containing SomeObject.class file. 0xCAFEBABE... If we use SomeObject on the JVM, it is loaded by the current classloader and all works fine. Now let's assume that I'd like to have some dynamic code generation. I can write my custom annotation @Target(ElementType.TYPE) public @interface Data { ... } and add it as a modifier to the class declaration: @Data class SomeObject { String name; } I can also retain it for the runtime with @Retention(RetentionPolicy.RUNTIME) : @Retention

for bytecode instrumentation in java, there is the asm framework and the bcel and javaassist libraries. However I need to do instrumentation in native code, since some java classes are already loaded by the time the javaagent runs, eg java.lang.Thread, java.lang.Class, etc is there any library for instrumenting java classes in native code? Edit: Seems there is a bit of confusion. What I want is: Create a native java agent, which uses JVMTI apis to change the bytecode of a class while its being loaded, using the OnClassLoad event hook. I encountered this problem during my doctoral research. The

I want to understand class files and inner/nested classes a bit better and I'm wondering about the following things: Is the InnerClasses attribute used to refer tothe inner/nested classes in the ´containing´ class or is it used in the inner/nested classes to refer to the ‘container’ class? Is the InnerClasses attribute in class files sufficient? E.g. Do inner/nested classes have to follow the name mangling with $ or is this just a convention? Is there a way to make a class look like an inner/nested class to the JVM without setting the InnerClasses attribute and does this depend on the JLM

App Engine uses a "precompilation" process with the Java bytecode of an app to enhance the performance of the app in the Java runtime environment. Precompiled code functions identically to the original bytecode. Is there any detailed information what this does? I found this in a googlegroups message : Yes, pre-compilation reduces the time to load an application. This will benefit you on your first request after a deploy, after you've been cycled out or if more application instances are created to scale up with your load. You will see up to 30% improved loading time on your first request. Pre

I'm writing a toy interpreter with a REPL in Java. I'd like to generate bytecode from the language and run that, instead of interpreting an AST and running that instead. Since my Java is a bit rusty, is it possible to run generated bytecode on the fly on the JVM? You can use java.lang.Classloader.defineClass(), which turns bytecode into a Class object. You can the call newInstance() on the resulting Class object, and off you go. Have a look at Javassist which contains a snippet compiler allowing you to compile Java snippets to bytecode and define them as a method in a class which you can then

I have written a Java bytecode parser using Haskell, and it works just fine. However the next step has me completely stumped. My Haskell program needs to modify the .class file so that, when executed, the Java program prints: " Entering [method name here] " before executing a method, and " Exiting [method name here] " after executing a method. All I know is that we will need to append the constant pool and method table with calls to System.out.println , but I feel I'm still missing something. What is the best way to approach this problem? How do you know how to call System.out.println in

When I observe my Java project byte code, I see the following byte code : java.lang.Object.()V java.lang.Boolean.(Z)V What is the meaning of <init>()V and <init>(Z)V java.lang.Object.()V is a void method ( V ) on java.lang.Object that takes no arguments. java.lang.Boolean.(Z)V is a void method on java.lang.Boolean that takes a single boolean ( Z since B is byte ) argument. In short, abc.def.WXYZ(IIIIIIIIIIIIII)J ^ ^ ^ target_class argument-types return_type See JNI Type Signatures for more detail. The JNI uses the Java VM’s representation of type signatures. Table 3-2 shows these type