1. CSC1030 HANDS-ON INTRODUCTION TO JAVA Loop, Primitive type & Object basics

2. Three Kinds of Looping Statements while (condition) { loop_body; } do { loop_body; } while (condition); for (start; condition; update) { loop_body; } Supplemented by: break; continue;

3. For example: while-loop class Main { public static void main (String [ ] args) { int i = 1; // declare a variable // a while-loop while ( i < 10 ) // while "i < 10 is true" { System.out.println(i); i = i + 1; // increment i } System.out.println(i); // what will i be? }

4. For example: do-while-loop class Main { public static void main (String [ ] args) { int i = 1; // declare a variable // a do-while-loop do { // do at least once System.out.println(i); i = i + 1; // increment i } while ( i < 10 ); // while "i < 10 is true" System.out.println(i); // what will i be? }

5. For example: for-loop class Main { public static void main (String [ ] args) { int i; // declare a variable // a for-loop (start; check; update) for ( i = 1; i < 10; i++ ) { // i runs from 1 to 9 System.out.println(i); } System.out.println(i); // what will i be? }

6. break and continue  break: stops a loop right away.  continue: stop the current iteration AND continue the next round!

7. Outline  The Java API  Using the Math Class Lab Exercise: Quadratic Equation Solver  Java Primitive Data Types  Java Class (Object) Types  Using the String Objects Lab Exercise: String Manipulation

8. The Java API  System, String, JOptionPane, etc. are stuffs provided in the Java Application Programming Interface (API). System.out.println(...); String answer; JOptionPane.showInputDialog(...);

9. The Java API Reference Manual http://java.sun.com/javase/6/docs/api/

10. The Java API Reference Manual Quick Reference Using NetBeans

11. Importance of the Java API  The API provides extra functionalities and tools, however.  As a Java programmer, we do NOT have to memorize all the stuffs provided in the API.  However, we should understand, look-up and make use of the API library properly.  Better though, we recite the spelling and usage of some commonly used ones, such as System, String, etc

12. Contributing to the World-Wide API  As a Computer Professional, sometimes we create something to make a contribution.  Others could then possibly make use of our work.  In such case, we have to well-design, well-test and well-document our contribution.

13. Outline  The Java API  Using the Math Class Lab Exercise: Quadratic Equation Solver  Java Primitive Data Types  Java Class (Object) Types  Using the String Objects Lab Exercise: String Manipulation

14. The Math Class  Well, System is a Java Class.  String is also a Java Class.  So as JOptionPane.  We are going to make use of another useful and important Java Class, the Math Class.

15. Using the Math Class class Main { public static void main (String [ ] args) { String deg; deg = JOptionPane.showInputDialog("An angle in deg:"); // convert the angle (text input) to a number double angle_in_degree; angle_in_degree = Double.parseDouble( deg ); double angle_in_radian; angle_in_radian = Math.toRadians( angle_in_degree ); System.out.println( "sin(" + deg + ") = " + Math.sin( angle_in_radian ) ); } sin(45) = 0.7071067811865475

16. Some Commonly Used Math Class Members  Math.toRadians( 270 ) Converts an angle measured in degrees to an approximately equivalent angle measured in radians.  Math.sin( 3.14159 ) A method giving us the trigonometric sine of an angle in radian.  Math.sqrt( 2.25 ) A method giving us the positive square root of a value.

17. Lab Exercise: Using Math with if

18. Break Time – 15 minutes

19. Outline  The Java API  Using the Math Class Lab Exercise: Quadratic Equation Solver  Java Primitive Data Types  Java Class (Object) Types  Using the String Objects Lab Exercise: String Manipulation

20. They are for storing numbers with a decimal point. They are for storing integers of different range limits.  Let's give the full list of the EIGHT Primitive Data Types in Java:  charboolean doublefloat byteshortintlong Java Primitive Data Types

21. What are Primitive Types?  Eight build-in types in Java: byte [-128  127] short [-32768  32767] int [-2147483648  2147483647] long [ - 9223372036854775808  9223372036854775807 ] float [±10 38 with floating point] double [±10 308 with floating point] char [‘A’, ‘B’, …, ‘a’, ‘b’, …, ‘0’, ‘1’, …, ‘!’, ‘#’] boolean [true, false]

22. Java Primitive Data Types  Variables in Java must bear a type.  Basically, we have these 8 types for declaring variables.  They are for storing different kind and different range of data.

23. The char Data Type  char is one of the primitive types representing a single character. char aVariable; aVariable = 'a'; char gender = 'F'; char grade = 'C'; char symbol = '#';

24. Outline  The Java API  Using the Math Class Lab Exercise: Quadratic Equation Solver  Java Primitive Data Types  Java Class (Object) Types: Quick Revision  Using the String Objects Lab Exercise: String Manipulation

25. Java Class (Object) Types  The primitive data types are good for representing simple data, such as a number, a character, a true/ false value.  In real life, information is usually not so simple.  Thus, we have to use some structured data types.  They are known as Class (Object) Types in Java.

26. Object-Oriented Programming  Object-oriented Programming (OOP) is one of the programming paradigms (school of thought, methodology) in computer science.  An object is used to store information as well as to keep methods for handling the information.  Synonyms:Object == Instance == Entity Class ~= Static ~= Type

27. Customer Bill Customer Michael Account 012-3-1441 Objects  Our world is full of objects. Graphical representation of objects Object ‘type’ Object name

28.  Our world is full of objects. Graphical representation of objects Customer Bill Objects Customer Michael Account 012-3-1441

29. Modeling Our World  We try to model this object world.  Objects can keep data/state and accomplish tasks. e.g. A drink dispensing machine has a stock of 100 cans. A drink dispensing machine sells Coke.  Inhuman?! Certainly, but it helps us to program a computer in an organized and manageable manner.

30. Classes  A class (e.g., Customer) is a kind of mold or template to create objects (e.g., Michael and Bill).  An object is an instance of a class. The object belongs to that class. Customer Bill Customer Michael Customer ‘instance-of’/ ‘belongs-to’ Class Object

31. More Class/ Object Examples Person Michael Person Bill Gates Person Account 019-9-5887 Account 217-1-1345 Account

32. Object-Oriented Programming  We first define classes.  While the program is running, we may create objects from these classes.  We may store information in objects.  We send messages to an object, instruct it to perform a task. (For example, we send a deposit $250.00 message to an Account object to add $250.00 into the account.)

33. Class (Object) Type Variables  There are already lots of classes defined in the Java API.  Let’s see how to make use of them. String address; address = "CUHK, Shatin, HK"; File aFile; aFile = new File("Hello.zip"); ZipFile aZip; aZip = new ZipFile(aFile); JButton aButton; aButton = new JButton("Ok");

34. Class (Object) Type Variables  With classes and the objects we created from the classes, we can represent, store and handle more complex form of data.  For example, we can represent some text using String, we can handle a ZIP file, we can process a JPEG image, we can show a button on the screen, etc.

35. Outline  The Java API  Using the Math Class Lab Exercise: Quadratic Equation Solver  Java Primitive Data Types  Java Class (Object) Types  Using the String Objects Lab Exercise: String Manipulation

36. Using the String Objects  Usually, an object is created from a class using the new( ) statement.  The String objects are different. They are privileged to use the double quotes for creation. String address; address = "CUHK, Shatin, HK";

37. Using the String Object Methods  There are many methods defined for String objects.  We can easily find out some properties of a String. String address; address = "CUHK, Shatin, HK"; char firstLetter; firstLetter = address.charAt(0); int addressLength; addressLength = address.length(); C 16

38. Lab Exercise: String Manipulation

39. Any Enquiry?