The Symbian OS (779886), страница 65
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Therefore, any look-and-feeldependent aspects of the MIDP implementation must be customizedfor the different variant user interfaces.• MIDlets should, as far as possible, look and feel like native applications. For Symbian OS, this poses a particular challenge sinceapplication look and feel ultimately depends on the variant userinterface which is running on a given Symbian OS device.• Symbian OS component APIs have a different design from MIDPAPIs, which requires an elaborate internal architecture to bind thefunctionality between those two orthogonal class hierarchies.• The Java ME subsystem as a whole can be swapped out and replacedby another. Symbian’s licensees are also at liberty to pick and choosewhich of the JSRs they use and which they do not.As well as overcoming these complications, the Java ME design mustmeet some basic design goals:• Support near-native behavior of MIDlets to enable seamless switchingbetween MIDlets and native applications• Provide the fullest possible implementation (MIDP specifies bothrequired and optional features) to ensure that the Java ME implementation on Symbian OS is highly competitive• Enable a ‘common platform’ by providing a solid core system on allSymbian smartphones• Provide customizability as an essential part of Symbian OS.
Licenseesmay choose to vary the degree to which they support Java on aparticular device by extending or limiting the default Symbian JavaME implementation, including removing or replacing it entirely.12.4 Evolution of Java on Symbian OSSymbian’s Java support has evolved with Java itself from the earliest daysof JDK 1.1.4, which had an AWT-based user interface implementation,to the PersonalJava and JavaPhone implementations of Symbian OS v6.The first MIDP 1.0 implementation on Symbian OS v7.0 (subsequentlybackported to Symbian OS v6.1) was followed by the arrival of MIDP 2.0in Symbian OS v7.0s.304THE JAVA ME SUBSYSTEMThrough Symbian OS v8 and v9, Java delivery evolved to a rich JavaME platform supporting a significant number of optional MIDP APIsand enhanced by the latest version of Sun’s CLDC 1.1 VM, which usesHotSpot technology.Although recently the emphasis has shifted towards Symbian’slicensees as the ultimate ‘owners’ of their own Java ME platforms, withSymbian focusing on the core of its delivery, Java has strengthened itsposition as an important element in any enterprise strategy, where rapiddevelopment and rollout of bespoke local applications is an importantdriver in the choice of devices.
It is also an important enabler for rapiddevelopment and easy deployment of small but high-value applications, including games and custom applications and services from themobile phone manufacturer and network operator, all of which help toconsolidate the position of Symbian OS in the market.Java provides a powerful model for acquiring mass business marketshare and building a technical platform. One of the important, originalunderlying goals for Symbian OS was to enable Java as a true platformfor developing Symbian OS applications, not simply as a lightweightplatform for running relatively trivial generic applications.Symbian (or Psion as it then was) was quick to recognize the significance of Java.
The success of its own OPL language2 and the emergenceof a strong third-party developer community was an important elementin the success of Psion’s Series 3 products. The follow-on 32-bit systemwas conceived from the beginning as an open development platformfor third-party application developers. At the same time, the complexity of its native C++ development environment and its unsuitability forsome kinds of application development was recognized early, as wasthe need for a rapid development alternative.
OPL support was presentfrom the beginning, following which a Visual Basic porting project wasstarted. However, attention moved to Java as a more powerful solutionfor third-party developers.Sun’s first release of Java appeared in early 1995 and the more stableJDK 1.0.2 release appeared in 1996. In early 1997, a few months beforethe first release of what was still known as EPOC32, Psion started its Javaport based on JDK 1.1.2. ‘Hello World’ first ran in July 1997 and thefirst graphical application ran in October of that year.
By the summer of1998, graphical applications were running on an upgraded version of theport, based on JDK 1.1.4, and in August 1998 certification was grantedby Sun. The first Java run-time system for EPOC32 was released in May1999.3 Demonstrations of Java applications running on early Symbian2OPL lives on as a rapid development language for Symbian OS, having been releasedunder an open source license by Symbian in 2003.
It can be found on the web atwww.allaboutopl.com/wiki/OPLWikiHome. See also [Spence 2005].3The full history of these early implementations can be found in earlier Symbianprogramming books, including [Tasker 2000] and [Allin et al. 2001].EVOLUTION OF JAVA ON SYMBIAN OS305OS smartphones caused quite a stir at the Symbian developer conferencein June 1999.4By that time, Psion had become Symbian and EPOC was evolvingtowards the first release of Symbian OS. However, porting Java hadnot been particularly easy.
For one thing, Sun had at first insisted on abinary-only license for the VM. Since the VM assumed an ANSI C/POSIXplatform, a basic C Standard Library implementation was needed tointerface it to Symbian’s native C++ APIs. Fundamental differences in thethread model between Java and Symbian OS posed further problems.
Andat that time, since the port was still based on ‘full-sized’ Java, graphicswere AWT-based. On a small platform, it was simply not possible toextract acceptable performance from AWT.Even before its first Java release for EPOC had shipped, Symbian hadstarted work, early in 1999, on a port of PersonalJava, a newly defined,scaled-down Java specification targeting smaller devices. In July 2000,PersonalJava together with an implementation of the JavaPhone API wasreleased as part of Symbian OS v6, appearing for the first time in a phoneproduct later that year in the Nokia 9210 Communicator.
JavaPhoneopened key Symbian OS APIs to Java applications, giving basic accessto the underlying address book, communications services and telephonyAPIs.PersonalJava was a first attempt to define a Java environment suitablefor constrained devices such as PDAs and mobile phones, and a forerunner of what eventually became Java ME. By the time of the first SymbianOS v7 release, the Java ME specification had been defined in terms ofMIDP/CLDC.
MIDP 1.0 was included for the first time in Symbian OSv7 and subsequently back-ported to earlier releases, appearing in theNokia 7650, based on Symbian OS v6.1. However, the PersonalJava andJavaPhone combination was still offered as an option to licensees.Symbian OS has tracked the evolution of the MIDP specification(indeed, as a member of the MIDP Expert Group, it has played anactive role in shaping it) through subsequent releases of the operatingsystem, supporting MIDP 2.0 for the first time in Symbian OS v7.0s,and extending its support in Symbian OS v8 and v9 with the additionof important optional packages, as well as improving the compatibility,interoperability and completeness of Java ME technology by providingsupport for the JTWI standard and increasing developer productivity bysupporting on-device debugging and standard integration with Java IDEsthrough the Unified Emulator Interface (UEI).MIDP 2.0 is a significant enhancement of the original MIDP specification.
In particular, it supports ‘push’ applications, in other words, MIDPapplications that are launched in response to ‘external’ events (i.e. events4The Java team demonstrated a Rubik Cube application, running in color on a PsionnetBook, to an enthusiastic audience.306THE JAVA ME SUBSYSTEMoriginating outside the application’s own process), for example, alarms,incoming messages or other network events.At the same time, the CLDC specification that defines the executionenvironment has evolved (again with Symbian participating as a CLDCExpert Group member). In practical terms, the most significant changeis the move in Symbian OS v7.0s from the KVM to CLDC-HI 1.0, withHotSpot VM technology, and in Symbian OS v8 to CLDC-HI 1.1.
Thecurrent CLDC1.1 configuration is likely to be the final configuration fromSymbian, although licensees may continue to evolve their own extensionsand track future evolution of the MIDP profile.12.5ArchitectureIn the Symbian OS system model (see Figure 12.1), Java ME is shownas a self-contained block spanning the UI Framework and ApplicationServices layers, which emphasizes the external view of Java ME as anapplication platform.The system model idealizes the representation of Java ME. As conventionally represented (see Figure 12.2), MIDP/CLDC forms a softwarestack that provides the execution environment for MIDlets; the CLDCconfiguration consists of the VM itself and the basic Java languageslibraries; the MIDP Profile defines the frameworks for application supportexpected from the device class and the various packages (both requiredand optional) providing the application APIs.UIFrameworkJava MEApplicationServicesOSServicesBaseServicesKernelServices &HardwareInterfaceFigure 12.1 Java ME in the system modelARCHITECTUREBluetoothSMSMobileMultifunction307PiMPackageRequired packagesMIDP 2.0 and MIDP 1.0 CompatabilityProfileCLDC ConfigurationConfigurationExtensionsVMFigure 12.2 High-level Java ME architectureFrom an internal architectural perspective, however, the Java MEimplementation hooks deeply into the supporting layers of the operatingsystem.
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