Java – in context Main Features From Sun Microsystems ‘White Paper’

Features: simple object oriented network-savvy interpreted robust secure architecture neutral portable high-performance multithreaded dynamic

The language itself Java does not allow pointers Java is strongly typed Java completely object-oriented Java prevents programmer from accessing a non-initialized variable

The Verifier When Java byte code arrives for execution the Verifier checks it to ensure that it is safe No dangerous pointers Access to private variables and methods valid Methods invoked with correct type parameters No illegal data conversions are done

The class loader The class loader carefully distinguishes between different packages and particularly between local built and classes and any others (it’s not nice to try to fool Java)

The Java Virtual Machine (JVM) Once code is checked, byte code is not directly executed on the machine but is interpreted

Arrays Subscripts must be within bounds

Garbage Collection When an object in a Java program is no longer needed, the system automatically releases the memory that was allocated to it. That memory can then be reused if needed

The filing system Java applet can control that applet’s access to files by specifying an option to the browser. The user can decide (for example) to read but not write to a local file (default applets can not read/write to users files unless given permission)

Summary Java provides several mechanisms for protection The language and the compiler – e.g. absence of pointers Verification of byte code The class loader The filing system and network access

Thin clients PCs connected to others rather than all stand alone PC does not need its own hard disk and filing system software. Organizations have hundreds of PCs (cost a factor) to upgrade hardware and software. Time spent to install software, file back ups etc. Thin client eliminates all these costs. Java strongly supports networking – and Java compilers can be downloaded

Microsoft vs. the world Text gives a very concise history of Windows O.S. and the Intel Corp. The U.S. government lawsuit now seems to have been settled. (individual states have not yet signed off) C# Microsoft OO language based on C++

Versions of Java 1. Standard 2. Enterprise 3. Micro (Personal Java for PDAs etc.)

Java capabilities Enhancements to Java through the addition of new libraries Java Libraries: (small language powered by) Java Language and Utilities Java Electronic Commerce Framework Java Security Java Media Framework Java Collections Framework Java 3D

Internationalization Different languages have different character sets Dates and times (UK day/month/yr – US month/day/yr) Currency Different currency symbols Java classes which help – Unicode character standard 1. Classes ‘locale’ an area with its own language classes do the appropriate formatting of currency, date and time 2. Unicode 16-bit (used for file I/O)

Databases – JDBC Databases are big business Aside from word processing, spreadsheets and the database can be regarded as the most vital software component of a business Java Database Connectivity (JDBC) JDBC allows access to SQL-compatible databases

RMI – Remote Method Invocation With the tremendous increase in Internet use. The idea of interacting with programs on other machines is mainstream. In the corporate computing area as well, networks are the norm. A possible arrangement for the drawing example in the text each PC (or server) would have a local program to handle drawings and one on the server to broadcast new input. (known as RMI user invokes methods on the server)

Java Beans ‘a reusable software component that can be manipulated visually in a builder tool’ The software into which a bean is to be placed is written in such a way as to allow the bean to be incorporated. To incorporate the bean into an application, a special bean development environment (BDK Beans Development Kit) from Sun

Java servlets Web interaction is enabled by programs on a server computer interacting with software (browser typical) on a client computer. Benefits: Each use of the Web page results in data being sent to server, the servlet produces a thread Servlet run in sandbox (safe and secure) Platform independent (if allowed)

Javascript Scripting language No language features common with Java Concepts similar to Java

Conclusion – trends in computer industry Tremendous growth of Internet Importance of Web interaction Use of intranets (within a corporation – example) Reduction in cost of networking Fusion of computer and telecommunications Incorporation (embedding) of computers within consumer products Multimedia

Conclusions - continued Vital need for secure computing across the networks Fight against Microsoft dominance (Windows O.S.) and Intel (PCs).