Abstract * Foil Index for this file
Secs 40.3
See also color IMAGE
Given by Nancy McCracken at CPS616 spring 1997 on Jan 22 1997. Foils prepared 1 February 97
Abstract * Foil Index for this file
Secs 40.3
See also color IMAGE
| What is Java! |
| Good Books |
| Java Compared to JavaScript |
| Language Characteristics (Why its Great) |
| Basic Applets and Graphics Classes |
| Language Syntax |
This table of Contents
Abstract
Secs 36
Full HTML Index
| Instructor: Nancy McCracken |
| teamed with Meryem Ispirli, Geoffrey Fox, |
| Tom Scavo, John Yip |
| Syracuse University |
| 111 College Place |
| Syracuse |
| New York 13244-4100 |
Secs 40.3
Full HTML Index
| What is Java! |
| Good Books |
| Java Compared to JavaScript |
| Language Characteristics (Why its Great) |
| Basic Applets and Graphics Classes |
| Language Syntax |
Secs 70.5
Full HTML Index
| Instructors: Geoffrey Fox |
| Nancy McCracken |
| Syracuse University |
| 111 College Place |
| Syracuse |
| New York 13244-4100 |
Secs 48.9
Full HTML Index
What is Java?
|
What is HotJava?
|
Secs 50.4
Full HTML Index
HotJava toolkit (1996-): class libraries for building web-aware applications i.e. The "Browser" class
|
| Natural Use of HotJava is for applications where it is critical to customize User Interface to a greater degree than Netscape allows |
| Netscape hopes you will use JavaScript to customize a core browser supplied by Netscape |
Secs 120.9
Full HTML Index
| Browsers (HotJava, Netscape 2.0/3.0 ..) supporting Java allow arbitrarily sophisticated dynamic multimedia applications inserts called Applets, written in Java, to be embedded in the regular HTML pages and activated on each exposure of a given page. |
Secs 48.9
Full HTML Index
Applet constructs are implemented in terms of a
|
Secs 28.8
Full HTML Index
Steps to running a Java Applet:
|
Using a Browser
|
Using appletviewer
|
Secs 59
Full HTML Index
| Starts in 1991 by Project Green --- a group in Sun that detaches from the main campus as a semi-autonomous task force focused on operating software for consumer electronic devices such as smart set-top boxes |
| Gosling (creator of Sun NeWS which had major conceptual impact both on current Java and Telescript models) realizes that C++ is not adequate and initiates development of a new language Oak, later renamed as Java. |
| A PDA (Personal Digital Assistant -- codename *7) based on Oak/Java ready in 1993. Green Team incorporates as FirstPerson, Inc. |
| *7 proposal to Time-Warner rejected in 1993. 3DO deal falls through in 1994. FirstPerson, Inc. dissolves. |
| Small group (~30 people, now Java Team) continues development and decides to adapt Oak as a Web technology. |
Secs 51.8
Full HTML Index
| An experimental web browser written in Java, called WebRunner and later renamed as HotJava, ready in 1994. |
| Java/HotJava published in April '95. |
| Netscape licences Java in May '95 and builds Java into Netscape 2.0 -- This confuses ownership and open-ness of Java |
| Beta JDK (Java Development Kit) published in summer/fall '95. It is better software but lower functionality than Alpha. |
| First alpha Java books appear in fall '95 such as a popular overview by SAMS and technical book "Java!" by Tim Ritchey, edited by New Riders. |
| Dec 4 1995 Business Week cover story on "Software Revolution --- The Web Changes Everything" exposes Java as a breakthrough force in the expanding Web/Internet. Also points out that "Java as a business" is yet to be defined. |
| In next week, SGI IBM Adobe Macromedia and finally Microsoft adopt/license Java. It appears that Java will be open and should be adopted by open Web community |
Secs 54.7
Full HTML Index
| Version 1.0 of JDK released January 96 by JavaSoft |
1.0 JDK should be the Internet standard and so compatible with ongoing Java implementations by all licensees, most notably Netscape. Beta/1.0 JDK includes:
|
Secs 41.7
Full HTML Index
| Hooked on Java, by Java developers Arthur van Hoff, Sami Shaio, Orca Starbuck, Addison-Wesley, is the (first) serious (but still rather high-level) book on beta Java. It contains example applets, but not much on programming. |
| Teach Yourself Java in 21 Days, by Laura Lemay and Charles L. Perkins, Sams.net Publishing, is a "how-to" book at the intermediate programming level. It concentrates on applets and windowing more than the object-oriented part of the language. |
| Java in a Nutshell, by David Flanagan, is the language reference book in the familiar O'Reilly series. |
Secs 72
Full HTML Index
The Java Programming Language, by Ken Arnold and James Gosling, Addison-Wesley, May 1996, has lots of details on the language basics for intermediate and advanced programmers. It covers threads and i/o packages, but not applets or windowing packages.
|
| Java Primer Plus, supercharging Web applications with the Java programming language, by Paul M. Tyma, Gabriel Torok, and Troy Downing, Sams.net, doesn't assume a lot of programming background, has chatty explanations and still covers lots of programming detail. |
| Java, How to Program, by Deitel and Deitel, Prentice-Hall, starts with beginning programming concepts and progresses rapidly through Java language. It has the most programming exercises. |
Secs 72
Full HTML Index
There are five books in the Java Series from SunSoft Press, Prentice-Hall.
|
| * this title is great, but what happened to "express Java", "Percolating through Java", and "Java for Drips"? |
Secs 56.1
Full HTML Index
| Netscape renames Livescript as Javascript and this is an interesting variant of Java which is fully interpreted (code can be included directly in HTML file)-- use for overall customization of client |
| Use Java for detailed programming and JavaScript for overall integration of client interface and system |
| JavaScript: Interpreted by client and NOT compiled |
Java: Compiled on Server before execution on client
|
| JavaScript: Object based -- no classes or inheritance -- built in extensible objects |
| Java: Object-oriented. Programs consist of object classes with inheritance |
Secs 25.9
Full HTML Index
| Document The Java: A White Paper by Sun Microsystems -- October 1995 draft by James Gosling and Henry McGilton -- enumerates the following main features of Java: |
| Simple and Familiar |
| Object-oriented |
| Architecture-neutral |
| Portable |
| Somewhat Interpreted |
| Distributed |
| Robust |
| Secure |
| High performance |
| Multi Threaded |
| Dynamic |
Secs 87.8
Full HTML Index
| Java omits several rarely used, poorly understood and confusing features of C++ including operator overloading, multiple inheritance, pointers and automatic type coercions. |
It adds automatic garbage collection which makes dynamic programming easier in Java than in C or C++.
|
| It also adds 'Interface' construct, similar to Objective C concept, which often compensates for the lack of multiple inheritance by allowing method calling syntax to be "inherited". |
| The resulting language is familiar as it looks like C++ but is simpler and hence easier to program in. |
| It also results in a much smaller kernel which is suitable for planned Java ports to consumer electronic devices. Base (alpha) interpreter is ~40Kb, libraries and threads add additional 175Kb. |
Secs 89.2
Full HTML Index
| Java model can be viewed as a C++ subset, with some dynamic elements inherited from Objective-C (method overloading, garbage collection). |
| Structures, Unions and Functions are absorbed into data and methods of Java classes -- Java is Simple! |
| The strength of Java object-oriented model is not is sophistication but in simplicity and the extensive class library associated with the system (some 250 public classes were released in both alpha and beta). |
| Java class plays also a role of a communication atom in the Web embedding model. Applet classes identify themselves by names in the HTML applet tag. Applet downloads other classes, present in the applet source. Hence, the Java class names play the role of addressing mode for the distributed Java code database. |
Secs 67.6
Full HTML Index
| C/C++ programming in a heterogeneous network environment requires use and compatibility across several vendor platforms and the corresponding compilers. This problem is solved in Java by designing platform-independent binary representation called Java bytecode (or opcode). |
| Java compiler (written in Java and platform-independent) reads Java source and generates Java bytecode. These bytecodes are shipped to client machines upon browser requests. |
| Each client machine must run Java interpreter which performs runtime execution of Java bytecodes. Java interpreter is written in POSIX compliant ANSI C and needs to be ported to and conventionally compiled (once) on each individual platform. |
| Once the interpreter is ported, application developers don't need to worry at all about platform specificity and differences between native compilers. |
Secs 86.4
Full HTML Index
| Java language offers a uniform abstract (virtual) machine model which is identical for all platforms. |
| SUN owns the Java Virtual Machine (see online report) -- it is universal while classes can be added by any user |
Unlike in C/C++ where various integers match the architecture of a physical machine at hand, Java byte, char short, int and long are always of the same size, equal to 8, 16, 16(unicode), 32 and 64 bits, respectively.
|
| Differences between vendor specific windowing environments (X Windows, MS Windows, Macintosh) are removed in terms of the Abstract Windowing Toolkit (AWT) metaphor. |
| AWT is given by ~60 Java classes (alpha) which offer a universal GUI programming model, portable between UNIX, PC and Mac, and translated automatically to native windowing systems on individual platforms by Java interpreters. |
Secs 11.5
Full HTML Index
| Java represents a compromise between fully compiled (like C/C++) and fully interpreted (like Smalltalk or Perl) models. |
| Java "compiler" produces a binary bytecode output which is portable and much smaller than the real binary for a specific machine (Typical bytecode size is of order of the original source code, within a factor of 2). |
| Java "interpreter" executes this bytecode and is therefore less dynamic than e.g. Perl interpreter (which performs an equivalent bytecode construction internally and on-the-fly when reading the program source). |
| In general, the compilation process is: a) time consuming and b) platform specific. Hence, interpreters are built and used to facilitate a) rapid prototyping and/or b) portability. Java model is focused on platform independence but the development throughput is also reasonable since the Java compiler is fast and generates compact bytecode output. |
Secs 24.4
Full HTML Index
| Popular TCP/IP based protocols such as FTP or HTTP are supported in terms of network protocol classes. This facilitates various forms of distributed processing. New protocols (e.g. PVM etc.) can added and dynamically installed. |
| Distributed computing model of Java is mainly client-server, with Java compiler preparing the opcodes at the server side, and Java interpreter executing it at the client side. |
| One can expect more dynamic uses of Java with Java threads on both Server and Client side communicating with each other. This is illustrated by Java based Collaboratory developed by Vishal Mehra as NPAC/Ece Master's Thesis |
Secs 48.9
Full HTML Index
| Java enforces compiler-time type checking and eliminates this way some error prone constructs of C/C++. |
| Pointer arithmetic is fully eliminated which allows e.g. for runtime checking of array subscripts and enforces security of the Java model. |
| Explicit declarations are always required, i.e. C-style implicit declarations are abandoned. This allows the Java complier to perform early error detection. |
| Rapid prototyping in Java is less natural than in JavaScript,Lisp, Tcl, Smalltalk or Perl, but the software quality assurance of Java is higher than in these more dynamic and 'forgiving' languages. |
Secs 116.6
Full HTML Index
Java bytecodes are shipped across the network and executed on client machines. Security is therefore a critical issue and strongly enforced in Java.
|
| Modifications of the C++ model such as eliminating pointer arithmetic and coercion were dictated mainly by the security requirements. |
| Most viruses are based on acquiring access to private/protected sectors of computer memory which is impossible in Java. |
| Java opcodes are executed at the client side by Java interpreter which operates exclusively on the virtual memory. Hence, unless there are security bugs in the Java interpreter itself, the model is safe and users cannot create security holes by incorrectly or maliciously written applets. |
| The bytecodes sent across network are verified at the client which prevents evil/corrupted classes from causing problems |
Secs 73.4
Full HTML Index
Java interpreter performs on-the-fly runtime execution of the Java bytecodes which results typically in a satisfactory performance.
|
| Support for generating native machine code out of Java bytecodes, viewed as intermediate compiler form, is also provided and useful for performance demanding applications. |
| The performance of the machine code, generated from Java bytecodes, is comparable to that offered by typical C/C++ compilers on the same platform. |
| Several of these concepts are in fact similar as in the OSF/ANDF project. Using ANDF terminology, we would call Java compiler a 'producer', and the machine code generator discussed here, an 'installer'. Default Java working mode doesn't use installers but directly interprets the intermediate form (this mode is supported in ANDF by GAI -- Generalized ANDF Interpreter). |
| Java/HotJava system implements ANDF concepts for the Java language. |
Secs 18.7
Full HTML Index
| Java model offers preemptive multithreading, implemented in terms of the Thread class. Thread methods offer a set of synchronization primitives based on monitor and conditional variable paradigm by C.A.R. Hoare. Java threads inherit some features from the pioneering Cedar/Mesa System by Xerox Park that gave birth to Macintosh and object-oriented programming. |
| A typical use of Java multithreading in applet programming is to have several independent but related simulations (e.g. various sorting algorithms), running concurrently in an applet window. Multithreading is also used internally by the browser to handle multiple document dynamics. |
| Another interesting application domain are multi-HotJava environments to come such as collaboratory or gaming. |
| Java threads don't have built-in point-to-point communication primitives. Various thread communication environments can be provided by coupling the thread and network protocol objects. |
Secs 28.8
Full HTML Index
| Java model is more dynamic than C++ and closer to Smalltalk or Perl. |
| Subclasses don't need to to be recompiled after superclass implementation is updated. |
| C++ has "fragile superclass" problem where must recompile children if change anything (method/instance variable) in a superclass or referenced class -- Java resolves references at runtime and avoids this. |
| Classes have runtime representation (implemented in terms of the Class class) which allows one to look up type of a given object instance at runtime (in C cannot know if pointer is to integer or browser!) |
Secs 28.8
Full HTML Index
| Instructors: Geoffrey Fox , |
| Nancy McCracken |
| Syracuse University |
| 111 College Place |
| Syracuse |
| New York 13244-4100 |
Secs 40.3
Full HTML Index
The original resource was the The Java Language Specification by Sun Microsystems, Inc., March 1995 updated to October 1995 but superceded by Gosling and Arnold Book
|
http://www.javasoft.com web site has plenty of references including
|
| Most of the books cited earlier have CDROM's with examples or the JDK. |
Secs 154
Full HTML Index
| All Java programs are written into a file with a ".java" extension. |
| Applications are .java files with a main class which is excuted first. |
How to compile and run a Java application:
|
| The resources javac and java are part of JDK and are not in Netscape and so are not necessarily available on the same machine as your web server. |
Secs 145.4
Full HTML Index
| Since Java is object-oriented, programs are organized into modules called classes, which may have data in variables and functions called methods. |
Secs 123.8
Full HTML Index
| Java applets are classes written in Java which are intended not to run as stand-alone programs (as applications do) but as subprograms of a browser which is already managing a window. |
| Applets should NOT have main method but rather init, start, paint etc. for displaying on the browser window |
The applet should be run through javac compiler getting a .class file as before:
|
| Also create an HTML file (say MyApplet.html) with an applet tag. |
Two ways to run an applet:
|
| This way we can compile on places with JDK installed but run almost anywhere! |
Secs 44.6
Full HTML Index
Given the following HTML
|
| Runs the "StockGraph.class" executable as an applet. |
| WIDTH and HEIGHT are attributes that are passed along to the applet. |
If the optional CODEBASE attribute is provided, then load the executable image from the directory specified by CODEBASE.
|
| Tag and attribute names are case insensitive. |
Secs 34.5
Full HTML Index
<APPLET CODE="StockGraph" WIDTH=200 HEIGHT=200
|
| Put a bunch of text here to be displayed by browsers such as Netscape 2.0 on Windows 3.1 that do not support Java |
| </APPLET> |
| ALT specifies text to displayed if the browser understands the applet tag, but if unable to run applets. |
| NAME specifies the name of this instance of the applet; This will make it possible for applets on the same page to find and communicate with each other. |
ALIGN specifies the alignment of the applet. The possible values are the same as those available in the IMG tag (top, middle, bottom, texttop, absmiddle, baseline, absbottom, left, right).
|
| VSPACE and HSPACE specifies the vertical and horizontal spacing in pixels, around the applet space. |
Secs 43.2
Full HTML Index
The applet tag can be followed by parameters:
|
The Java program accesses this information by
|
| Typically this processing would be in init() method of Applet |
Secs 169.9
Full HTML Index
| Java applets are part of the class hierarchy that can call methods to display on a screen (within the browser window). This example defines the public method paint in this class and calls a method drawString defined in the class Graphics. |
Secs 83.5
Full HTML Index
| You should name the file with your applet name, HelloWorldApplet.java, run the compiler (javac), getting a bytecode file HelloWorldApplet.class, which you put in a web directory. |
Secs 80.6
Full HTML Index
| Lexical structure inherits a lot from C/C++. There are however some notable differences which are listed below. |
| Java characters are based on 16--bit wide Unicode Worldwide Character Encoding rather than the usual 8--bit wide ASCII. |
| This allows full support of all alphabets and hence all languages |
Three types of comments are supported:
|
| for /** */ one inserts HTML documentation with some simple macros such as @see (to designate see also) BEFORE the method or class being documented |
Secs 61.9
Full HTML Index
| Source code of a Java program consists of one or more compilation units, implemented as files with .java extension. |
Each compilation unit can contain:
|
| Java compiler (called javac) reads java source and produces a set of binary bytecode files with .class extensions, one for each class declared in the source file. For example, if Foo.java implements Foo and Fred classes, then "javac Foo.java" will generate Foo.class and Fred.class files. |
| Suppose that Foo implements an applet and Fred is an auxiliary class used by Foo. If HotJava/Netscape encounters a tag <APPLET code="Foo.class">, it will download Foo.class and Fred.class files and it will start interpreting bytecodes in Foo.class. |
Secs 72
Full HTML Index
Each Java variable or expression has a definite type. There are three "types" of types!
|
First we discuss the Primitive Types
|
| One can use casts such as longint = (long) i; // which can be explicit as here and sometimes implied (see later) |
| Note booleans are either TRUE or FALSE -- they are not 0, 1 ,-1 ... |
Secs 141.1
Full HTML Index
| Arrays are "true" or "first class" objects in Java and no pointer arithmetic is supported. |
An Array is declared as:
|
| alternative syntax: int[] vec; |
and created by:
|
or concisely:
|
Arrays of arbitrary objects can be constructed,
|
Secs 89.2
Full HTML Index
| An array of length 128 is subscripted by integers from 0 to 127. |
| Subscripts are range checked in runtime and so vec[-1] and vec[128] will generate exceptions. |
Array length can be extracted via the length instance variable, e.g.
|
Arrays can have dynamic sizing (a fixed size determined at runtime)
|
Multidimensional arrays are arrays of arrays
|
Secs 90.7
Full HTML Index
| Java's expressions are very similar to C and the following are valid: |
| 2+3 |
| (2+3)*i |
| i++ /* equivalent to i = i +1 */ |
| (i > 0 ) && (j>0) /* Boolean */ |
| i <<1 /* Left shift by 1 binary digit */ |
| (i>0) ? true:false /* conditional expression */ |
| i >>> 2 /* Signed right shift by 2 binary digits */ |
| "fred" + "jim" is "fredjim" |
| /* + Equivalent to . in Perl */ |
| (a instanceof B) /* True iff object a is of class B */ |
Secs 72
Full HTML Index
| if(some boolean expression) {..} |
| else if(another boolean) {..} |
| else {...} |
| while(any boolean) {/*DoStuff*/} |
| do {/*Whattodo*/} while(another boolean); |
| for(expression1; booleanexpression ; expression2) {...} |
| naturally starts with expression1, applies expression2 at end of each loop, and continues as long as booleanexpression true |
| switch (expression) { /* Just as in C */ |
| case Constant1: /* Do following if expression=Constant1 */ |
| /* Bunch of Stuff */ |
| break; |
| case Constant2: /* Do following if expression=Constant2 */ |
| /* Bunch of Stuff */ |
| break; /* ....... */ |
| default: |
| /* Bunch of Stuff */ |
| break; |
| } |
Secs 44.6
Full HTML Index
| One can break out of an iteration of a (nested) for loops in fashion offered by Perl but with a different syntax |
| outer: // label |
| for( int j=0; j<10; j++) { /* Note j only defined in for loop */ |
/* select course j */
|
| /* Continue jumps to here to next iteration of loop labelled with outer */ |
| } |
Secs 66.2
Full HTML Index
| An object of the graphics class represent a rectangular drawing grid, with a coordinate system in pixels. |
| When you draw objects, there is a current "state" consisting of a font and a color. |
Secs 133.9
Full HTML Index
| Fonts and colors are objects (sometimes called instances) of the font and color class in the awt package. |
Secs 84.9
Full HTML Index
| Methods are available for drawing lines, rectangles, rounded rectangles, ovals, arcs, and polygons. This example draws a rectangle filled with green with a black border, and a circle filled with magenta. |
Secs 17.2
Full HTML Index
| Within the applet tags, any number of param tags may occur. Attributes can control the alignment of the applet window on the html page. |
Secs 54.7
Full HTML Index
| A standard method, init(), is executed when your applet is loaded; it can call the method getParameter. |
Secs 18.7
Full HTML Index
| The method applet.size() returns the width and height as a dimension object, which has width and height variables. FontMetrics has variables for various attributes of the font, including width and height. |
Secs 67.6
Full HTML Index
Each applet's flow of control goes through a sequence of standard methods:
|
| There are also standard methods repaint (), which calls update(), which blanks out the old drawing and calls paint. |
Secs 90.7
Full HTML Index
| This example fills the applet's drawing area with square boxes, each of which has a randomly chosen color. |
Secs 61.9
Full HTML Index
| This demonstrates 2-dimensional arrays by first filling arrays with random colors, and then drawing, uses a fixed size drawing window for simplicity. |