rina zviel-girshin @asc1 system development with java instructors: rina zviel-girshin...

Rina Zviel-Girshin @ASC 1

System development with Java

Instructors: Rina Zviel-Girshin

Interdiciplinary Center HerzliaSchool of the Computer Science

Fall: 2001-2002


Information Source

• Course site : www.idc.ac.il/

• Course book:

Java Software Solutions /Lewis & Loftus

Thinking in Java / Bruce Eckle


Course Methodology

• Non-LinearitySpiral model

Hypermedia

• CAI – Computer Assisted Instruction

• Interactive learning

• Labs and programming

• Multi-approach: inductive-deductive trails


Programming Languages and Java

• Programming languages

• Java language

• The basic program

• Java syntax


Programming

• The process of writing programs called a programming.

• The process requires:Programming languageA translator of the programming language

into machine language• Programs are written in programming language.


Syntax

• Syntax describes the grammatical rules of a language.

• Valid words• Valid grammar constructions• Valid punctuation

• Programs must be syntactically correct.


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.


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.


Programming languages

• There are several families of the programming languages:

Procedural ( Pascal, C++, Java)

Logical ( Prolog) Visual ( Visual Basic) Document (HTML, LATEX)


Programming languages

• Procedural languages can be divided into:Machine languagesLow-level (Assembler )Intermediate-level (C)High-Level (C++, Java)


Java

• Java is high-level language.• Java is object oriented language.• In this course we will use the terms:

– OOP,

– OOA ,

– OOD.


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).


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.


OOP

Objects are the building blocks of:

the problemthe solutionthe input sourcethe output targetthe environment


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)


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.


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.


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.


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.


Java advantages

• Platform independent““Write once, run anywhere”.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.”


Java disadvantages

• The main Java disadvantage:

Efficiency concerns.Efficiency concerns.

Looking to the future:

VM performance will improve.


Java environments

• Java has many environments. • The number grows as Java evolves. • Among them are:

• Text applications• Beans• Applets• GUI Applications• Packages


Two main environments

The two main environments: Web Browser Operating System


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).


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.


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.


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.we will return to the details later.


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


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.


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?”);

}

}


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?”);

}

}

Our program will becalled My

A comment


Java program structure

• A Java program is made up of one or more classes.

• Classes have names.• The ‘My’ program consists of one class named

‘My’.


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.


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.


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?”);


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



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).



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


AppletsThe program has to import two packages:• applet.Applet• awtThe program (the class) has to extend the Applet

class, using the following syntax:public class My extends Applet{ // your code}


Basic applet code

The final code looks like this:

import java.awt.*;

import java.applet.*;

public class My extends Applet

{

// your code

}



• 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.


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


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>

</APPLET>


HTMLThe call to applet has to be in HTML file.The file can look as follows:<HTML><HEAD><TITLE>Java applet test page</TITLE></HEAD><BODY><APPLET

CODE="HelloWorld.class"WIDTH=150 HEIGHT=50>

</APPLET></BODY></HTML>


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.


Java Compiler

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


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.


Compile-interpret-execute cycle

Java soursecode

Javacompiler

Java bytecode

javac My.java

My.java

My.class


Java soursecode

Javacompiler

Java bytecode

Javainterpreter

javac My.java

java My

My.java

My.class

Compile-interpret-execute cycle


Errors

• A program can have three types of errors:• Syntax and semantic errors – called compile-

time errors• Run-time errors – occur during program

execution• Logical errors


Errors

• Compile-time errors occur during program compilation and an executable version of the program is not created.

• Run-time errors occur during program execution and cause abnormal program termination.

• Logical errors occur during program execution and produce incorrect results.


Java Syntax

• To write without syntax mistakes you have to know Java syntax.

SyntaxSyntax -

the study of the patterns of formation of sentences and phrases from words and of the rules for the formation of grammatical sentences in a language.


Java Syntax

• Case-sensitive• Semi-colon (;) is line terminator• Curly braces ({,}) used for block structure• Several keywords


Comments

There are two kinds of comments: • /* text */ A traditional comment: all the text from

the ASCII characters /* to the ASCII characters */ is ignored.

• // text An end-of-line comment: all the text from the ASCII characters // to the end of the line is ignored.


Comments

Comments do not nest. • /* and */ have no special meaning in comments

that begin with //. • // has no special meaning in comments that begin

with /* or /**.

As a result, the text: /* this comment /* // /** ends here: */is a single complete comment.


Identifiers

An identifier is:an unlimited-length sequence of Java letters

and Java digits, the first of which must be a Java letter.

An identifier cannot have the same spelling (Unicode character sequence) as:

• a keyword, • boolean literal, • the null literal


Unicode

• Letters and digits may be drawn from the entire Unicode character set (The character set that uses 16 bit per character).

• Identifier can be written in most writing scripts in use in the world today, including:

Hebrew,Chinese, Japanese, KoreanPractically all languages


Identifiers examples

• Uppercase and lowercase are different.

All the following are different identifiers:

MY my My mY my1

Examples of identifiers are:

Strings i3

isLetterOrDigit מונה

MAX_VALUE


KeywordsThe following are reserved words called keywords

and cannot be used as identifiers:

abstractbooleanbreakbytebyvaluecasecastcatchcharclassconstcontinue

defaultdodoubleelseextendsfalsefinalfinallyfloatforfuturegeneric

gotoifimplementsimportinnerinstanceofintinterfacelongnativenewnull

operatorouterpackageprivateprotectedpublicrestreturnshortstaticsuperswitch

synchronizedthisthrowthrowstransienttruetryvarvoidvolatilewhile


True, False, Null

While true and false might appear to be keywords, they are technically Boolean literals.

Similarly, while null might appear to be a keyword, it is technically the null literal.


Literals A literal is a source code representation of a value of:

• a primitive type,• the String type,• the null type

Kinds of Literals: IntegerLiteral FloatingPointLiteral

BooleanLiteral CharacterLiteralStringLiteralNullLiteral


Integer Literals

An integer literal may be expressed in:• decimal (base 10), • hexadecimal (base 16), • octal (base 8)


Hexadecimal numeral

• A hexadecimal numeral consists of the leading characters 0x or 0X followed by one or more hexadecimal digits.

• It can represent a positive, zero, or negative integer. • Hexadecimal digits with values 10 through 15 are

represented by the letters a through f or A through F, respectively.

HexDigit is one of:

0 1 2 3 4 5 6 7 8 9 a b c d e f A B C D E F


Octal numeral

• An octal numeral consists of a digit 0 followed by one or more of the digits 0 through 7.

• It can represent a positive, zero, or negative integer.

• Octal numerals always consist of two or more digits.


Example

Examples of int literals:

02 0372

0xDadaCafe 1996

0x00FF00FF • the same number in decimal octal hexadecimal:

3 03 0x3

15 017 0xF


Zero

• 0 is always considered to be a decimal numeral.• The numerals 0, 00, and 0x0 all represent exactly

the same integer value – zero value.


Floating-Point Literals• A floating-point literal has the following parts:

• a whole-number part, • a decimal point (represented by an ASCII period character), • a fractional part, • an exponent (is indicated by a letter e or E followed by an

optionally signed integer),

• and a type suffix. • At least one digit, in either the whole number or

the fraction part, and either a decimal point, an exponent, or a float type suffix are required. All other parts are optional.


Floating-Point Literals

• A floating-point literal is of type float if it is suffixed with an ASCII letter F or f; otherwise its type is double and it can optionally be suffixed with an ASCII letter D or d.

Examples of float literals:

1e1f 2.f .3f 0f 3.14f 6.022137e+23f


Boolean Literals

• The boolean type has two values, represented by the literals true and false

• A boolean literal is always of type boolean.

BooleanLiteral is one of:

true false


Character Literals

• A character literal is expressed as a character or an escape sequence, enclosed in single quotes.

• A character literal is always of type char.

Examples of char literals:

'a‘ '%‘ '\t‘ '\\‘ '\u03a9‘

'\uFFFF‘ '\177'


String Literals • A string literal consists of zero or more characters

enclosed in double quotes. • A string literal is always of type String.

Examples of string literals: "" // the empty string

"This is a string" // a string containing 16 characters

"This is a " + // actually a string-valued constant expression,

"two-line string" // formed from two string literals


Escape Sequences for Character and String Literals

Escape Sequence:\ b /* \u0008: backspace BS */\ t /* \u0009: horizontal tab HT */\ n /* \u000a: linefeed LF */\ f /* \u000c: form feed FF */\ r /* \u000d: carriage return CR */\ " /* \u0022: double quote " */\ ' /* \u0027: single quote ' */\ \ /* \u005c: backslash \ */


The Null Literal

• The null type has one value, the null reference, represented by the literal null, which is formed from ASCII characters.

• A null literal is always of the null type.


Separators

The following nine ASCII characters are the separators (punctuators):

( ) { } [ ] ; , .


Operators

The following 37 tokens are the operators, formed from ASCII characters:

= > < ! ~ ? :

== <= >= != && || ++

-- + - * / & |

^ % << >> >>> += -=

*= /= &= |= ^= %=


Programming style

• Java is a free-format language. • There are no syntax rules about how the program

has to be arranged on a page. You can write entire program in one line.

• But as a matter of good programming style, you should lay out your program on the page in a way that will make its structure as clear as possible.


Programming style

• Some advises:• Put one statement per line. • Use indentation to indicate statements that

are contained inside control structures. • Write comments.• Give your variables names that make sense.


Style ExampleBad:

public class

Stam

{ public static void

main(String args[]){System.out.println("Hello!“);}}

Better:

// style example – outputs “Hello!”

public class Hello

{

public static void main(String args[])

{

System.out.println("Hello!");

}

}


Any Questions?

rina zviel-girshin @asc1 system development with java instructors: rina zviel-girshin...

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