CSC1030 HANDS-ON INTRODUCTION TO JAVA

1. CSC1030HANDS-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 Manualhttp://java.sun.com/javase/6/docs/api/

10. The Java API Reference ManualQuick 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 sin(45) = 0.7071067811865475 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 ) ); } }

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. Java Primitive Data Types • Let's give the full list of the EIGHTPrimitive Data Types in Java: • char boolean double float byte short int long They are for storing numbers with a decimal point. They are for storing integers of different range limits.

21. What are Primitive Types? • Eight build-in types in Java: byte [-128  127] short [-32768  32767] int [-2147483648  2147483647] long [-9223372036854775808 9223372036854775807 ] float [±1038 with floating point] double [±10308 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. 012-3-1441 Bill Michael Customer Customer Account Objects • Our world is full of objects. Graphical representation of objects Object name Object ‘type’

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

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. Customer Bill Michael Customer Customer 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. Object Class ‘instance-of’/ ‘belongs-to’

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

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