JAVA虚拟机外文翻译资料

Wireless Sensor Networks (WSNs) have played an important role in diverse domains. However, programming on WSN nodes are quite hard because currently there exist no standard software and hardware platforms in WSN. Thus its essential to build a software infrastructure that can provide a decent development environment to the users.

无线传感器网络（WSN）已在不同领域发挥了重要作用。然而基于无线传感器网络节点的编程是很困难的，因为目前WSN领域还不存在统一的软件和硬件平台。因此，很有必要建立一个软件基础架构，用于提供一个统一的开发环境给用户。

Wireless sensor network (WSN) consists of spatially distributed sensor nodes which can monitor the environmental or physical conditions as well as transmit the collected sensor data cooperatively through the wireless network to a central location. It has played a more and more important role in widespread domains such as industrial control, precision agriculture, smart care, military battlefield surveillance, etc.

无线传感器网络（WSN）能够监测环境或身体状况，以及通过所述无线网络协作发送所收集数据到传感器网络中的处理节点上。其应用领域广泛，在工业控制，精准农业，智能保健，军事战场监视等方面发挥着越来越重要的作用

Experience shows that programming on WSN nodes is quite hard for the WSN users. Firstly, the hardware platforms in WSN are diverse which makes it complicate to program on WSN platforms because the programmers, who may not be the experts, are required to understand the various low-level hardware details. Secondly, no standard software platform is so far provided, e.g., for the operating system (OS) in WSN, there are currently TinyOS, Contiki, SOS and MantisOS, etc. Each system differs from the others not only in the design concepts but also the supported application programming style. Thus it is significant to provide a decent development environment to the WSN users to simplify the application programming process.

经验表明，WSN编程对于WSN用户来说比较困难。首先，WSN的硬件平台多样性导致基于WSN平台的编程比较复杂，毕竟编程人员不可能都是这方面的专家，他们需要了解底层平台的信息后才能着手开发。其次，迄今为止没有统一的软件开发平台。举个例子，目前WSN的常用系统平台有TinyOS, Contiki, SOS和MantisOS。每个系统从设计理念到开发细节都有区别。所以很有必要给WSN用户提供一个像样的开发环境来简化WSN应用程序的开发过程。

One efficient method to facilitate the application development is to implement an embedded Java Virtual Machine (EJVM) on the WSN nodes. This is reasonable since on one hand, EJVM enables programming in high-level object- oriented JAVA language which not only performs sound, robust, and reusable software but also be enjoyed widely among the programmers due to its widespread popularity and familiarity. On the other hand, EJVM supports platform- independent application that can address the challenge of programming in heterogeneous environments.

一种有效的改进WSN应用开发的方法是在WSN节点上运行一个嵌入式Java虚拟机(EJVM)。这么做是因为一方面，基于EJVM可以使用久经考验的面向对象语言JAVA进行应用程序开发。另一方面，EJVM使得应用程序与平台无关，可以解决异构WSN导致的开发困难的问题。

However, two important challenges for implementing EJVM on WSN nodes exist. The first is that WSN nodes are commonly memory and energy resource-constrained devices while most EJVMs perform a non-trivial memory space and executive efficiency overhead. The second is that most WSN applications have essential performance requirements, e.g., the support of application programming in multitasking model and the ability to process critical events in low latency. Therefore, the WSN system infrastructure based on EJVM should be able to meet these requirements. Because of these challenges, choosing a suitable EJVM in terms of the applied environments and analyzing the feasibility before the actual implementation is indispensable.

然而，在WSN节点上运行EJVM存在着两大挑战。其中之一是WSN节点的存储空间和能源极度受限。另外一个是WSN应用程序有必须的性能需求，例如低能耗运行多任务和低延迟处理关键事件。因此基于EJVM的WSN基础设施都有这些需求。由于这些挑战，实施挑选一个适合的EJVM之前必须参考环境情况和分析可行性。

Many kinds of JVMs have been developed currently for embedded devices, such as FijiVM, JamaicaVM, Squawk JVM, leJOS,DarjeelingVM, NanoVM, TakaTuka JVM, simpleRTJ, KESO VM, Sentilla VM, etc. And these VMs strike different balances between the supported features and required platform resources.

目前给嵌入式设备开发的JVM有很多很多，例如FijiVM、JamaicaVM、Squawk JVM、leJOS、DarjeelingVM、NanoVM、 TakaTuka JVM、simpleRTJ、KESO VM、Sentilla VM,而这些虚拟机在支持特性和资源需求方面都有好多不一样。

For the supported features, some VMs focus on the time- critical application dominantly, such as Fiji VM and JamaicaVM. Some comply with the connected limited device configuration (CLDC) Java Micro Edition configuration, such as Squawk JVM and TakaVM. Some implement a clean room of JVM, such as simpleRTJ, while some sacrifice part features like static synchronized method and floating point supports for better executive eficiency, e.g., Darjeeling. The diverse supported features make these VMs be suitable for distinct application environments as well as have different memory resource requirements.

JVM所支持的特性很多很多，有的虚拟机更多关注时间关键型应用，如FiJi VM和JamaicaVM。有的则符合连接有限的设备配置(CLDC) JavaME的配置,比如 Squawk JVM和TakaVM。有的虚拟机则和空房间一样，例如simpleRTJ，有的像Darjeeling那样，则是通过牺牲了一部分JVM的特性和功能（静态同步方法和浮点支持）来提供更好的执行效率。支持的不同特性使这些虚拟机适用于不同的应用程序环境以及有不同的内存资源需求。

SimpleRTJ is a real-time Java VM/OS as well as a clean room implementation of JVM. Meanwhile, it targets at small embedded and consumer devices.

SimpleRTJ是一个实时Java虚拟机（系统），就像一个什么复杂功能都没有的JVM，也就是说，它是面向嵌入式消费设备。

For the pre-linked code, simpleRTJ links all the Java classes that comprise the application image together and replaces the symbolic references with the relative offsets or indexes during the post-compile process, depicted in Fig. 1. Compared with dynamic method, pre-linked mechanism decreases the flexibility of Java program in case the Java application is needed to be updated or extended in class granularity, yet much lower resource consumption is reached which is more practic

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