Rina System development with Java Instructors: Rina Zviel-Girshin Interdiciplinary Center Herzlia School of the Computer Science Fall:

Rina Information Source Course site : Course book: Java Software Solutions /Lewis & Loftus Thinking in Java / Bruce Eckle

Rina Course Methodology Non-Linearity Spiral model Hypermedia CAI – Computer Assisted Instruction Interactive learning Labs and programming Multi-approach: inductive-deductive trails

Rina Programming Languages and Java Programming languages Java language The basic program Java syntax

Rina Programming The process of writing programs called a programming. The process requires: Programming language A translator of the programming language into machine language Programs are written in programming language.

Rina Syntax Syntax describes the grammatical rules of a language. Valid words Valid grammar constructions Valid punctuation Programs must be syntactically correct.

Rina Semantics Semantics gives the meaning of what you write with a language. A programming language must precisely define the meaning of every statement that can be written with it. Programs must be semantically correct.

Rina Example The following sentence is syntactically correct but semantically incorrect. “ Java programs are green and yellow.” –All words are correct words. –Punctuation is correct. –But logically the sentence makes no sense.

Rina Programming languages There are several families of the programming languages: Procedural ( Pascal, C++, Java) Logical ( Prolog) Visual ( Visual Basic) Document (HTML, LATEX)

Rina Programming languages Procedural languages can be divided into:  Machine languages  Low-level (Assembler )  Intermediate-level (C)  High-Level (C++, Java)

Rina Java Java is high-level language. Java is object oriented language. In this course we will use the terms: – OOP, – OOA, – OOD.

Rina OOA and OOD OOA- Object-Oriented Analysis is a way to analyze a problem. OOD- Object-Oriented Design is a way to design a solution. Both see the world as: objects and their relations (behavior, communication).

Rina OOA and OOD (cont) The way to analyze a problem is to define the objects relevant to it and their behavior. The way to solve a problem is to realize the objects relevant and the behavior we need. Both are useful as preliminary stages in OOP- Object Oriented Programming.

Rina OOP Objects are the building blocks of:  the problem  the solution  the input source  the output target  the environment

Rina Objects Objects include both: data (fields, variables, state) processing (behavior, methods, functions) Objects have two kinds of behavior: outer – I/O, messages, relations with others inner – processing (usually computing the messages)

Rina Objects (cont) Relations between objects are implemented using communication (messages). Communication can have many forms. Some forms are very different from the usual idea of a message. Objects acquire structure using their relations. The structure is usually tree-like.

Rina High-level languages Writing programs in machine language is possible but very difficult and time consuming. Programs usually written in a more human readable language - high-level language. Java is high-level language. A program written in any computer language must be translated into a machine language in order to be executed.

Rina Translators Compiler A compiler is a program that translates a source program (usually high level language) into target program (usually machine language program). The resulting program can be executed many times. Interpreter An interpreter is a program that reads, translates and executes the source program statement by statement. The translation is done each time the program runs.

Rina Java Java is a high-level, third generation programming language, like C, Fortran, Smalltalk. Shares much of C's syntax. Designed by a group at Sun MicroSystems. Originally called Oak.

Rina Java advantages Platform independent “Write once, run anywhere”. Improve robustness, remove unsafe language loopholes. According to Sun: “ Java is simple, object-oriented, distributed, interpreted, robust, secure, architecture-neutral, portable, high-performance, multithread, and dynamic language.”

Rina Java disadvantages The main Java disadvantage: Efficiency concerns. Looking to the future: VM performance will improve.

Rina Java environments Java has many environments. The number grows as Java evolves. Among them are: Text applications Beans Applets GUI Applications Packages

Rina Two main environments The two main environments:  Web Browser  Operating System

Rina Web Browser In the browser environment the browser acts as an intermediate between the program and the operating system. The JVM resides inside the browser. The program can be simpler. The program has to work in graphical mode. The program is called “Applet” (a small application).

Rina Operating System In the operating system environment the program is called “application”. Application has a more rigid structure. Application can be textual or graphical. Application is less secure.

Rina Learning Java The specific challenge is twofold:  Learning the language technical aspect: the large set of new features class libraries classes methods which are provided as part of the language.  Learning to maximize the benefits of the object- oriented paradigm.

Rina OOA and OOD vs. OOP OOA is a way of analyzing - OOD is a way of thinking – OOP is a way of doing. OOA is about “why” – OOD is about “what” – OOP is about “how”.

Rina Starting to Program The basic idea of the course is to start programming as soon as possible. At first you will have to take a lot of things on trust. Promise: we will return to the details later.

Rina Java programs All Java programs have three parts: Auxiliary prescriptions A class – an envelope around the other components Code per se – Optionally – other components which include the instructions themselves Instructions to be executed

Rina Writing a Java Program Use an editor to type the program code. Save the code file. Compile the file with Java language compiler. Fix the bugs! Run the program.

Rina A basic Java Program // Prints “How are you?” to the screen class My { public static void main (String[] args) { System.out.println(“How are you?”); }

Rina A basic Java Program // Prints “How are you?” to the screen class My { public static void main (String[] args) { System.out.println(“How are you?”); }

Rina Java program structure A Java is made up of one or more classes. Classes have names. The ‘My’ program consists of one class named ‘My’.

Rina Class structure A Java class contains one or more methods. Methods have names too. The program (the class) has to have a main method. The method is called (surprisingly) – main.

Rina Main The main method has a standard syntax: public static void main(String args[]) {… // your code } There can be only one main per file. The main method contains the code to be executed when the program runs.

Rina Method structure A method contains one or more statements. The main method of My program has a single statement: System.out.println(“How are you?”);

Rina Stages of Writing and Executing Assumptions: Using only the basic JDK software Assuming the JDK was installed properly In the WIN/DOS environment Class name is My File name is My.java Directory (folder) name is c:\java

Rina Stages of Writing and Executing 1.Open a text editor that can produce a plain text file (such as Notepad). 2.Create a source code file with the extension on the file name being.java. The file has to have the same name as the outer class. 3.Start a the DOS command environment by opening MSDOS prompt (using the Start->Programs->MSDOS Prompt series of choices).

Rina Stages of Writing and Executing 4.Change directory to the directory containing the source file. 5.Compile the file, using the prompt command: javac My.java 6.The result is My.class in the same folder. 7.Run using the prompt command: java My

Rina Applets The program has to import two packages: applet.Applet awt The program (the class) has to extend the Applet class, using the following syntax: public class My extends Applet { // your code }

Rina Basic applet code The final code looks like this: import java.awt.*; import java.applet.*; public class My extends Applet { // your code }

Rina Stages of Writing and Executing Applet can’t be run directly. Applet has to be run in Browser and by the Browser. Web browser executes web pages. Web page should call the applet code.

Rina Call to applet The call to applet consist of: –the command APPLET –the name of the applet class –the dimensions of the panel in which the applet will run

Rina Example Assuming the name of the applet class is HelloWorld.class the call to applet looks like this: <APPLET CODE = "HelloWorld.class" WIDTH = 150 HEIGHT= 50>

Rina HTML The call to applet has to be in HTML file. The file can look as follows: Java applet test page <APPLET CODE="HelloWorld.class" WIDTH=150 HEIGHT=50>

Rina Execution Assuming the file is called HelloWorld.html 1.The stages common to all, described above. 2.Open the file HelloWorld.html in the Browser.

Rina Java Compiler The Java compiler is called javac. Java programs are compiled to byte code.

Rina Byte code The Java compiler translates Java program into a special representation called byte code. Java byte code is a machine code for Java virtual Machine(JVM). VM is a platform-specific tool to interpret the byte code and to translate it to commands for certain processor and OS. The use of the byte code makes Java platform independent.

Rina Compile-interpret-execute cycle

Rina Compile-interpret-execute cycle

Rina Any Questions?