1 Class 6

2 Objectives Objectives Identify, declare, and use primitive data types Use the System class to create data streams Use the Scanner class of functions to handle user input

3 Chapter Objectives Convert strings to numbers using the parse() method Use assignment statements to store data with proper identifiers Use operators and parentheses correctly in numeric and conditional expressions Round an answer using the round() method of the Math class

4 Introduction Data are collections of raw facts or figures A program performs operations on input data to output information Input data can come from a variety of sources –The program itself –Users of the program –External files

5 Variables Variables are like storage locations in the computer’s memory.

6 Naming Rules of Variables First character must be one of the letters a-z, A-Z, or an underscore ( _ ) or a $ After first character use a-z, A-Z, 0-9, underscore ( _ ) or $ Any length Keep them meaningful

7 Variable Rules (con’t) Case sensitive –ItemsOrder does not equal itemsorder Cannot declare two variables of the same name in a method Cannot give a variable the same name as a method

8 Intrinsic Data Types JAVA has eight intrinsic data types, which form the basis for all other data types (i.e., classes): 1.boolean: - a 1 byte value that is assigned a value of either true or false (both are JAVA defined values). Boolean values have no direct conversion to integer values, and are initialized to false.

9 Intrinsic Data Types 2.byte: - a 1 byte integer, capable of representing numbers from numbers from -128 to It is initialized to 0. 3.char: - a 2 byte integer that is normally used to represent character values using the Unicode system (the first 128 values of which correspond to ASCII values). It is initialized to \u0000.

10 Intrinsic Data Types 4.short: - a 2 byte integer, able to represent numbers between -32K and +32K. It is initialized to 0. 5.int: - a 4 byte integer, able to represent numbers between -2 billion and +2 billion. It is initialized to 0.

11 Intrinsic Data Types 6.long: - an 8 byte integer, capable of representing numbers between -2 and +2. It is initialized to 0. 7.float: - a 4 byte IEEE format real number, giving about 7 decimal digits of precision. It is initialized to 0.0f. 63

12 Intrinsic Data Types 8.double: - an 8 byte IEEE format real number, giving about 15 decimal digits of precision. It is initialized to 0.0d.

13 Key JAVA Operators Operator Description Example ( ) Parenthesis (X+2)/3

14 Key JAVA Operators Operator Description Example * Multiply X*2

15 Key JAVA Operators Operator Description Example / Divide X/12

16 Key JAVA Operators Operator Description Example % Modulus 7%3

17 Key JAVA Operators Operator Description Example + Add X+7

18 Key JAVA Operators Operator Description Example - Subtract X-6

19 Key JAVA Operators Operator Description Example > Greater than X>3

20 Key JAVA Operators Operator Description Example < Less than X<3

21 Key JAVA Operators Operator Description Example >= Greater than or equal X>=3

22 Key JAVA Operators Operator Description Example <= Less than or equal X<=3

23 Key JAVA Operators Operator Description Example == Equals X==3

24 Key JAVA Operators Operator Description Example != Not equal X!=3

25 Key JAVA Operators Operator Description Example = Assignment operator Y=X+3

26 The Body Mass Index Calculator An interactive program –Accepts the weight and height from the user –Calculates the BMI to gauge total body fat –Displays the result

27 The Body Mass Index Calculator Three versions –Input/Output using the command prompt –Input/Output using dialog boxes –Web environments use an applet interface

28 (b) console application using dialog boxes (a) console application in a command prompt window (c) applet

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30 Problem Analysis Convert user input to metric measurements Calculate the BMI Display the result

31 Design the Solution Design the three kinds of user interfaces with storyboards Design the logic of the program –Use pseudocode for sequential flow for all programs –Use an event diagram for the applet Validate the design –Compare the program design with the original requirements

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33 Coding the Program Import the java.io package –Provides classes to support system input and output Add a throws IOException clause to the method header –Warns the compiler that the possibility of input or output errors exists –Gives the program the opportunity to handle input or output errors during run-time without aborting

34 Coding the Program

35 Storing Data Java is a strongly typed language –Variables must be declared with a data type –Variable locations can hold only that data type Java has two categories of data types –Primitive data types hold single data items Integers, characters, floating point, and booleans are primitive types –Reference data types hold a value that refers to the location of the data All Objects and arrays are reference types

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37 Declaring Variables

38 User Input – Streams and the System Class The act of data flowing in and out of a program is called a stream The System class creates three streams when a program executes

39 User Input – Streams and the System Class Data from input streams are first sent to a buffer The java.io package contains several stream classes –InputStreamReader Decodes the bytes from the System.in buffer into characters –BufferedReader Increases efficiency by temporarily storing the input received from another class, such as InputStreamReader Aids in platform independence by simplifying the process of reading text and numbers from various input sources

40 Using the BufferedReader class Call the BufferedReader constructor to instantiate a BufferedReader object The argument of the BufferedReader() method instantiates an InputStreamReader BufferedReader() returns a reference to the input data from System.in

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42 User Prompts, Inputs, and Conversions The readLine() method reads a line of input text and returns a String containing the line The returned String must be explicitly converted if the data is to be used as another data type Each primitive data type has a wrapper class allowing the primitive to be treated as an object The wrapper classes provides a parse() method to convert Strings to primitives, and vice versa –Example: height = dataIn.readLine(); inches = Integer.parseInt(height);

43 Assignment Statements General syntax: location = value

44 Arithmetic Operators

45 Arithmetic Operators The order of operator precedence is a predetermined order that defines the sequence in which operators are evaluated in an expression Addition, subtraction, multiplication, and division can manipulate any numeric data type When Java performs math on mixed data types, the result is always the larger data type Casts allow programmers to force a conversion from one primitive type to another

46 Comparison Operators A comparison operation results in a true or false value that can be stored in a boolean variable

47 Numeric Expressions Numeric expressions evaluate to a number Only numeric primitive data types may be used in a numeric expression A value and variable must be separated by an arithmetic operator Unless parentheses supercede, an expression is evaluated left to right with the following rules of precedence: –Multiplication and/or division –Integer division –Modular division –Addition and/or subtraction

48 Conditional Expressions Conditional expression evaluate to either true or false Comparison operators, values, variables, methods, and Strings may be used in a conditional expression Two operands must be separated by a comparison operator Unless parentheses supercede, an expression is evaluated left to right with relational operators (, >=) taking precedence over equality operators (==, !=)

49 Parentheses in Expressions Parentheses may be used to change the order of operations –The part of the expression within the parentheses is evaluated first Parentheses can provide clarity in complex expressions –Numeric and conditional expressions should be grouped with parentheses Parentheses can be nested –Java evaluates the innermost expression first and then moves on to the outermost expression

50 Construction of Error-Free Expressions Java may not be able to evaluate a validly formed expression due to the following logic errors: –Dividing by zero –Taking the square root of a negative value –Raising a negative value to a non- integer value –Using a value too great or too small for a given data type –Comparing different data types in a conditional expression

51 The Math Class

52 Using Variables in Output

53 Compiling, Running, and Documenting the Application Compile the Body Mass Index Calculator program Execute the program Test the program by entering the sample input data supplied in the requirements phase at the prompts Verify the results Print the source code and screen images for documentation

54 Using Swing Components Save the previous version of the Body Mass Index Calculator with a new filename Import the javax.swing.JOptionPane class –Contains methods to create dialog boxes for input, confirmation, and messages Delete the IOException and BufferedReader code –The swing dialog boxes buffer data from the user and handle IO errors

55 Swing Dialog Boxes Dialog boxes are created with the JOptionPane “show” methods The showInputDialog() and showConfirmDialog return a String containing the user input

56 Swing Dialog Boxes

57 Closing Programs that use Swing System.exit() terminates an application that displays a GUI –The command prompt window closes when this method is called System.exit accepts an integer argument that serves as a status code –0 indicates successful termination –1 indicates abnormal termination

58 Saving, Compiling, and Running the Swing Version Verify that the file name matches the class name at the beginning of the code Compile the source code Test with the same sample data for all versions to compare output results If incorrect or unrealistic data is entered by the user, errors will occur –Errors and exception handling will be discussed in a later chapter

59 Moving to the Web The applet version of the Body Mass Index Calculator has four kinds of objects – Image, Labels, TextFields, and Buttons Import three packages –Java.applet –Java.awt –Java.awt.event Implement an ActionListener interface in the class header –Informs the program to respond to user- driven events

60 Moving to the Web Every event class has one or more associated listener interfaces

61 Moving to the Web

62 Adding Interface Components to an Applet Label –Displays text in the applet window TextField –Displays a text box for users to enter text Buttons –Displays a command button for users to click

63 The init() Method Initializes the window color and graphic Adds components to the applet window Registers the Button’s ActionListener

64 The actionPerformed() Method When a click event occurs, the ActionListener’s actionPerformed() method is triggered –Input values are retrieved with getText() –Calculations are performed –Output is sent to a label with setText()

65 The paint() Method Draws the initialized image in the applet window

66 Creating an HTML Host Document for an Interactive Applet Compile the applet Write an HTML Host Document to execute the applet –Use the tag to specify the bytecode file, and width and height of the window Use the same sample data to test the applet Document the source code

67 File Management Coding and compiling an application creates several files on your storage device File naming conventions and the operating system’s capability of displaying icons can help the programmer maintain a logical order –Three java files named after the program purpose and user interface type –Three class files after compilation –HTML host document –Image file

68 Conclusion of Class 4