Java Virtual machine Learning

There is no perfect program in the world, but we are not frustrated because writing a program is a process that is constantly striving for perfection.

Advantages of Java:

(1) write in sequence, run in multiple places

(2) provides a relatively secure memory management and access mechanism to avoid the vast majority of memory leaks and pointer cross-border issues

(3) Hot spot Code detection and runtime compilation and optimization, which allows the Java application to achieve higher performance with the increase of running time

(4) A complete set of application interfaces, as well as countless third-party libraries from commercial organizations and open source communities to help it achieve a wide variety of functions

Java Technology System:

(1) Java programming language

(2) Java virtual machines on various hardware platforms

(3) class file format

(4) Java API class Library

(5) Third-party Java libraries from commercial organizations and open source communities

Java Virtual Machine Development:

(1) Sun Classic VM: The first commercial Java Virtual machine, can only use the pure interpreter to execute Java code, after the JIT compiler, JIT will take over the virtual machine execution system, the interpreter will no longer work

(2) When exact vm:jdk1.2, a virtual machine named exact VM was not issued on the Solaris platform

(3) Hotspot VM: In JDK1.2, the classic VM coexists with the HotSpot VM, but the classic VM is used by default, while at JDK1.3, the hotspot VM is the default virtual machine, and the classic VM is reserved until JDK1.4 The Classic VM completely exits the historical stage of the commercial virtual machine and enters the Sun Labs in the VM with the exact VM.

High-performance Java virtual machines generally refer to the Sun HotSpot, BEA JRockit, IBM J9 Vm,jrockit VMs, once known as the "world's fastest Java Virtual machine", is a dedicated server hardware and server-side application scenarios highly optimized attack, Due to the focus on the server-side application, it is not too concerned about the program startup speed, so JRockit internal does not include the implementation of the parser, all the code by the Instant compiler table execution, while the JRockit garbage collector and Missioncontrol service suite and other parts of the implementation, are the leading position; virtual machines such as Azul VMS and Bea Liquid VMS are "high-performance" virtual machines.

Looking ahead to the future of Java technology:

(1) Modular

In the future Java platform, it is possible to provide syntactic support for modularity

(2) Mixed language

When a single Java development has been unable to hide the complexity of the current software requirements, more and more Java Virtual machine-based language development is applied to software projects, such as: Scala, Groovy, Clojure, jruby/rails

(3) Multi-core parallel

As early as JDK1.5, the Java.util.concurrent package has been introduced to implement a coarse-grained concurrency framework, and the inclusion of Java.util.concurrent.forkjoin package in JDK1.7 is an important extension of this framework.

(4) Further enrichment of grammar

Java 5 Once expanded the Java syntax by adding auto-boxing, generics, dynamic annotations, enumerations, variable-length parameters, For-each traversal, and more

(5) 64-bit virtual machine

Java Virtual machine Learning