Overview. Software Code is Everywhere. Software Crisis. Software crisis Development approaches Reusability Java packages API Sample classes:

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1 Overview Software crisis Development approaches Reusability Java packages API Sample classes: String, Random, StringBuffer, StringTokenizer 8 November 2007 Ariel Shamir 1 Software Code is Everywhere Televisions: 500Kb of software Electric Shaver: 2Kb Power train cars: lines of computer code 100 millions of instructions space station 75 mercury 50 gemini 25 space shuttle apollo November 2007 Ariel Shamir 2 Software Crisis IBM consulting group: survey of 24 leading companies developing large distributed systems: 55% of the projects cost more than expected 68% overran their schedules 88% had to be substantially redesigned No important critical statistic: how reliably did complete systems ran? 8 November 2007 Ariel Shamir 3 1

2 Why? Software systems, from an engineering point of view, are perhaps the most complex machines ever built by humans Dynamic nature: requirements change constantly Complex inputs and outputs, complex processes Failure to expect the unexpected No one manager can comprehend the entirety - traditional development processes break down No quality control and productivity measurements 8 November 2007 Ariel Shamir 4 Program Life Cycle Development Use Maintenance 8 November 2007 Ariel Shamir 5 Maintenance Maintenance tasks include any modifications to an existing program. It includes defect removal (debugging) and enhancements Maintenance efforts tend to far outweigh the development effort in today s software Small increases in effort at the development stage can greatly reduce maintenance tasks 8 November 2007 Ariel Shamir 6 2

3 Build and Fix Approach Too many programmers follow a buildand-fix approach: They write a program and modify it until it is functional, without regard to system design Errors are addressed as they are discovered It is not really a development model at all!! 8 November 2007 Ariel Shamir 7 Waterfall Approach Establishing clear and unambiguous requirements Creating a clean design from the requirements Implementing the design Testing the implementation 8 November 2007 Ariel Shamir 8 Waterfall Diagram Establish requirements Create design Implement code Not realistic!! Test system 8 November 2007 Ariel Shamir 9 3

4 Iterative Approach Allows the developer to backtrack and cycle through the different development stages Establish requirements Create design Implement code Test system 8 November 2007 Ariel Shamir 10 Possible Solutions Brute-force approach to bug removal: Beta versions: hordes of users dig up the glitches QA departments Use formal methods - translate requirements and code to a language which can be analyzed mathematically Put more emphasis on requirements and design to avoid problems later 8 November 2007 Ariel Shamir 11 Reusability Another option is to promote reusability Mass production of software must rely on interchangeable, reusable, and aging components, which are already tested and robust If you do not have to write everything from scratch, you can concentrate on the important tasks OOP: reusability of small components is built in the language! 8 November 2007 Ariel Shamir 12 4

5 Java API (Packages) Java comes with 3,000+ pre-designed components. The Java API is the library of classes supplied by Java. The classes in the Java API is separated into packages. Each package contains a set of classes that are related in some way. 8 November 2007 Ariel Shamir 13 The Java API Packages java.applet java.awt java.beans java.io java.lang java.math... java.net java.rmi java.security java.sql java.text java.util 8 November 2007 Ariel Shamir 14 Example Packages java.lang:general java.applet : Programs that transported across the Web. java.awt:graphics, windows, GUI. java.math: Calculations, math. java.net: Communication. 8 November 2007 Ariel Shamir 15 5

6 Documentation: List of Packages Details of Packages List of Classes 8 November 2007 Ariel Shamir 16 java.lang Choose java.lang from list of Packages Details of Classes List of Classes defined in Package 8 November 2007 Ariel Shamir 17 String Class Class Hierarchy Class Documentation 8 November 2007 Ariel Shamir 18 6

7 String Methods Methods List 8 November 2007 Ariel Shamir 19 Importing Packages Using a class from the Java API can be accomplished by using its fully qualified name: java.util.random random = new java.util.random(); Or the class can be imported once with the import statement at the top of the file: import java.util.random;... Random random = new Random(); 8 November 2007 Ariel Shamir 20 Importing Packages You can also import all the classes in a given package with a single import statement: import java.util.*; The java.lang package is automatically imported into every Java program. 8 November 2007 Ariel Shamir 21 7

8 The Random Class A program may need to produce a random number (DiceSimulation.java). The Random class provides methods to simulate a random number generator. The nextint method returns a random number from the entire spectrum of int values. Usually, this number is be scaled and shifted to the desired range. 8 November 2007 Ariel Shamir 22 Random Class Example import java.util.random; // This program simulates a tossing of a dice class DiceSimulation { static final int NUMBER_OF_TOSSES = 10; public static void main(string[] args) { int sum; int count = 0; Random random = new Random(); 8 November 2007 Ariel Shamir 23 Random Class Example while(count<=number_of_tosses) { int result = Math.abs(random.nextInt())%6+1; sum = sum + result; System.out.println( The sum of tosses is +sum); 8 November 2007 Ariel Shamir 24 8

9 The String Class A character string in Java is an object, defined by the String class String name = new String ("Ken Arnold"); Because strings are so common, Java allows an abbreviated syntax: String name = "Ken Arnold"; Java strings are immutable; once a string object has a value, it cannot be changed! 8 November 2007 Ariel Shamir 25 String Class Example String sentence = Houston, we have a problem. ; int length = sentence.length(); // length=27 String word = sentence.substring(0,7); //= Houston word = word.tolowercase(); // word = houston ; char c = word.charat(2); // c = u boolean b = word.equals( Houston ); // b=false int index = sentence.indexof( we ); word = sentence.substring(index, index+3); // = we word = word.trim(); // word= we 8 November 2007 Ariel Shamir 26 String Conversions Type To String From String boolean String.ValueOf(boolean) new Boolean(String). booleanvalue() int String.ValueOf(int) Integer. long String.ValueOf(long) Long. ParseInt(String,int base) ParseLong(String,int base) float String.ValueOf(float) new Float(String).floatValue() double String.ValueOf(double) new Double(String).doubleValue() 8 November 2007 Ariel Shamir 27 9

10 String Conversion Example String s = "100"; int i = Integer.parseInt(s,10); long ii = Long.parseLong(s,10); s = " "; Double d_obj = new Double(s); double d = d_obj.doublevalue(); float f = new Float(s).floatValue(); 8 November 2007 Ariel Shamir 28 More Conversions boolean b = false; int i=100; double d=123.45; char c= x ; String s1=string.valueof(b), //s1== false s2=string.valueof(i), //s2== 100 s3=string.valueof(d), //s3== s4=string.valueof(c); //s4== x 8 November 2007 Ariel Shamir 29 The StringBuffer Class String class is immutable. The StringBuffer class allows to use dynamic strings - which can be modified: append(char c) insert(int index, char c) charat(int index) setcharat(int index, char c) reverse() length() 8 November 2007 Ariel Shamir 30 10

11 StringBuffer Class Example StringBuffer text1 = new StringBuffer(); StringBuffer text2 = new StringBuffer( m ); StringBuffer text3 = new StringBuffer( 1 dollar ); text1.append(1); text1.append( p ); text1.append( e ); text1.append( n ); text1.append( ny ); 8 November 2007 Ariel Shamir 31 StringBuffer Class Example text2.insert(0,1); text2.insert(2, di ); text3.insert(5, e ); System.out.println(text1); System.out.println(text2); System.out.println(text3); text3.reverse(); System.out.println(text3); 8 November 2007 Ariel Shamir 32 Example Output 1 penny 1 dime 1 dollar rallod 1 8 November 2007 Ariel Shamir 33 11

12 More Scanner Class We have seen that the Scanner class is defined in the java.util package. The Scanner class can also be used to break up a string into pieces called s. By default the delimiters for the s are the white space characters (space, tab, new line). It can also be used to read from files (more on this later). 8 November 2007 Ariel Shamir 34 Break to Words Example input: Hello, my name is Dani. output: Hello, my name is Dani. 8 November 2007 Ariel Shamir 35 Scanner Programming Example String poem = Que sera sera, whatever will ; Scanner = new Scanner(poem); String ; while (.hasnext()) { =.next(); System.out.println(); 8 November 2007 Ariel Shamir 36 12

13 String poem = Que sera sera, whatever will be will be ; Scanner = new Scanner(poem); String ; Que sera sera, whatever will Value not defined 8 November 2007 Ariel Shamir 37 while (.hasnext()) { Que sera sera, whatever will hasnext() true 8 November 2007 Ariel Shamir 38 =.next(); sera sera, whatever will next() Que 8 November 2007 Ariel Shamir 39 13

14 =.next(); sera sera, whatever will Que 8 November 2007 Ariel Shamir 40 while (. hasnext()) { sera sera, whatever will hasnext() Que 8 November 2007 Ariel Shamir 41 while (.hasnext()) { sera sera, whatever will true Que 8 November 2007 Ariel Shamir 42 14

15 =.next(); sera, whatever will next() sera Que 8 November 2007 Ariel Shamir 43 =.next(); sera, whatever will sera Que 8 November 2007 Ariel Shamir 44 =.next(); sera, whatever will sera Que 8 November 2007 Ariel Shamir 45 15

16 =.next(); sera, whatever will sera 8 November 2007 Ariel Shamir 46 =.hasnext(); sera, whatever will hasnext() sera 8 November 2007 Ariel Shamir 47 =.next(); whatever will sera, sera 8 November 2007 Ariel Shamir 48 16

17 =.next(); whatever will sera, sera 8 November 2007 Ariel Shamir 49 =.next(); whatever will sera, sera 8 November 2007 Ariel Shamir 50 // This program gets a sentence from the // user and output each word in the // sentence on a separate line. import java.util.scanner; class BreakSentence { public static void main(string[] args) { Scanner scan = new Scanner (System.in); System.out.println("Please enter a sentence"); String sentence = scan.nextline(); Scanner = new Scanner(sentence); String ; while (.hasnext()) { =.next(); System.out.println(); 8 November 2007 Ariel Shamir 51 17

18 // This program gets a sentence from the // user and output each part separated by // a comma on a separate line. import java.util.scanner; class BreakSentence { public static void main(string[] args) { Scanner scan = new Scanner (System.in); System.out.println("Please enter a sentence"); String sentence = scan.nextline(); Scanner = new Scanner(sentence);.useDelimiter("\\s*,\\s*"); String ; while (.hasnext()) { =.next(); System.out.println(); 8 November 2007 Ariel Shamir 52 18