I would like to know what are the loop optimizations performed by Oracle Java 7 (or 8) Hotspot VM?

Is there a difference between java.vendor and java.vm.vendor properties in Java? It appears that the two are always the same. Is that a correction assumption? If you know of scenarios where thes...

I am building an application which can transfer data between a mobile and a Wi-Fi device... The mobile has got the AP enabled (through code) and another device connects to this specific network... ...

If anyone can give me brief information about the advantages and disadvantages of the two JVM since they all depend on the Standard JVM Specification.

I've been reading through the sun.misc.Unsafe class (openjdk6) as I was curious how many native methods it actually referred to. Understandably there are a large number of native methods in the cla...

I am going through the JIT HotSpot compiler logs (-XX:+PrintCompilation -XX:+UnlockDiagnosticVMOptions -XX:+PrintInlining) to make sure an important/hot method is being optimized/compiled. The meth...

Imagine that we have a 1000 objects of the same type scattered across the memory (they were created at different times and other objects have been created in between). We have an array which holds ...

For both on-heap and off-heap allocations. On-heap - in the context of three major garbage collectors: CMS, Parallel Old and and G1. What I know (or think that I know) to the moment: all object ...

Java 8 reserves 1G for Metaspace just after it starts. It means that minimum metaspace size is 1G. But I set up MetaspaceSize to 300m and MaxMetaspaceSize to 400m. Why Java reserves more then I all...

Given the following code: public class Test{ static int[] big = new int [10000]; public static void main(String[] args){ long time; for (int i = 0; i < 16; i++){ time = System.nanoTime()...

C malloc implementations typically don't allocate the precise amount of memory requested but instead consume fixed-size runs of memory, e.g. with power-of-two sizes, so that an allocation of 1025 b...

We run a web application with a JVM backend (Java 7 update 75; code is in Scala, but I don't believe this is relevant). We use Google for authentication via Oauth. There have been a handful of day...

Compiling the following interface: package test; public interface MyInterface { public void foo(); } and checking the compiled code using javap -v -s test.MyInterface shows the following (-s p...

I am using -XX:+PrintGCApplicationStoppedTime and -XX:+PrintGCApplicationConcurrentTime options to turn on gc logging. But found that only after 4 0r 5 prints of PrintGCApplicationStoppedTime my a...

I was trying to understand the memory structure of HotSpot JVM and got confused with the two terms "Method Area" and "PermGen" space. The docs I referred to say that Method Area contains the defini...

Watching Towards a Universal VM presentation, I studied this slide, which lists all the optimisations that HotSpot JIT does: In the language-specific techniques section there is a de-reflection. I...

After upgrading to Java 1.8.0_20 our test system reported errors, but the code was not changed. I found out, that Math.pow() called with exactly the same input parameters yields different results u...

I am using the following JVM parameters to start-up a JVM with the hostpot debugger. -Xdebug -Xrunjdwp:server=y,transport=dt_socket,address=0 Note that I am assigning port zero, so that the JVM ...

I'm developing a JavaFX desktop application using Java 7. The application I'm developing uses 10-12 background threads which gets system information or makes HTTP request. I also use some JNA and J...

(Note that when I say "JVM", I really mean "Hotspot", and I'm running the latest Java 1.6 update.) Example situation: My JVM is running with -Xmx set to 1gb. Currently, the heap has 500mb allocat...

I've set the max heap to 8 GB. When my program starts using about 6.4 GB (as reported in VisualVM), the garbage collector starts taking up most of the CPU and the program crashes with OutOfMemory w...

I got this error when I try to reload class (hot swap) with changed method bodies in my project. Before everything works fine, but suddenly it stop and I don't remember nothing what could be a caus...

I'm trying to build a JIT strategy based on method structure with profiling info (provided by JVM) but i didn't able to trigger JIT manually. This documentation says i can run JIT by invoking java....

Regarding JLS ch17 Threads and Locks, it says "if one action happens-before another, then the first is visible to and ordered before the second"; I wonder: (1) What does it really mean by saying "...

Well my doubt is this one: In Java, it is disallowed to inherit from an array, ie, one can't do things like: class FloatVec extends float[] { // Vector methods. } FloatVec somevec = new FloatVe...