There are several reasons. First off, it’s not necessary for performance. The JVM already optimizes things at runtime, so there’s no point in adding redundant complexity to the compiler. However, another major reason noone has mentioned here is debugging. Making the bytecode as close to the original source as possible makes it a lot easier … Read more
Try specifying a garbage collector manually. Concurrent Mark Sweep is a good general purpose one that provides a good balance between low-pause and reasonable throughput. If you are on Java 7 or later Java 6, G1 collector is probably better since it is able to also prevent memory fragmentation. You can check the Java SE … Read more
This is what I think is happening (keep in mind I’m not familiar with HotSpot): 0xf36c9fd0: mov 0x6c(%ecx),%ebp ; vfoo 0xf36c9fd3: test %ebp,%ebp ; vfoo is null? 0xf36c9fd5: je 0xf36c9ff7 ; throw NullPointerException (I guess) 0xf36c9fd7: movl $0x1,0x8(%ebp) ; vfoo.x = 1 0xf36c9fde: mov 0x68(%ecx),%ebp ; sz 0xf36c9fe1: inc %ebx ; i++ 0xf36c9fe2: test %edi,0xf7725000 … Read more
It just selects the “Server Hotspot VM”. See documentation (Solaris/Linux) for java. According to Wikipedia: Sun’s JRE features 2 virtual machines, one called Client and the other Server. The Client version is tuned for quick loading. It makes use of interpretation, compiling only often-run methods. The Server version loads more slowly, putting more effort into … Read more
Here is a working “hello world” made with ObjectWeb ASM (a library which I recommend): package hello; import java.lang.reflect.Method; import org.objectweb.asm.ClassWriter; import org.objectweb.asm.Label; import org.objectweb.asm.MethodVisitor; import org.objectweb.asm.Opcodes; public class HelloWorldASM implements Opcodes { public static byte[] compile(String name) { ClassWriter cw = new ClassWriter(0); MethodVisitor mv; cw.visit(V1_6, ACC_PUBLIC + ACC_SUPER, “hello/HelloWorld”, null, “java/lang/Object”, null); cw.visitSource(“HelloWorld.java”, … Read more
The following will list all the providers and the algorithms supporter. What version of Java are you using? Unless you’re on an old version JCE should be included as standard. import java.security.Provider; import java.security.Security; public class SecurityListings { public static void main(String[] args) { for (Provider provider : Security.getProviders()) { System.out.println(“Provider: ” + provider.getName()); for … Read more
jvm.dll is the actual Windows implementation of the JVM (or better, the main entry point). C or C++ applications can use this DLL to run an embedded Java runtime, and that would allow the application to interface directly with the JVM, e.g. if they want to use Java for its GUI. java.exe is a wrapper … Read more
Idiomatic Clojure favors defining independent functions that operate on a very small set of core data structures; this unbundling of methods and data is a strong statement against object orientation and in favour of a functional style. Rich Hickey (creator of Clojure) has repeatedly stated the importance of this; for example here: “Clojure eschews the … Read more
You can run with -XX:+PrintFlagsFinal to print the values of all flags at startup of the JVM. Alternatively, you can use the jinfo tool to check the value of a flag in a running JVM: > jinfo -flag UseCompressedOops 7364 -XX:+UseCompressedOops Use jps to find the pid of the process.
Disclosure – I’m the vert.x guy 🙂 Vert.x is a fully fledged platform for building polyglot, scalable, asynchronous web-enabled applications. It is heavily inspired from node.js but goes further than node.js and provides a distributed event bus which reaches from the server right into client side JavaScript thus creating a super simple model for so-called … Read more