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

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Class 6Class 6

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ObjectivesObjectivesIdentify, declare, and use primitive

data typesUse the System class to create data

streamsUse the Scanner class of functions

to handle user input

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Chapter ObjectivesChapter ObjectivesConvert strings to numbers using the

parse() methodUse assignment statements to store data

with proper identifiersUse operators and parentheses correctly

in numeric and conditional expressionsRound an answer using the round()

method of the Math class

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IntroductionIntroductionData are collections of raw facts or figuresA program performs operations on input

data to output informationInput data can come from a variety of

sources

– The program itself

– Users of the program

– External files

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VariablesVariables

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

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Naming Rules of VariablesNaming Rules of VariablesFirst 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

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Variable Rules (con’t)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

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Intrinsic Data TypesIntrinsic Data TypesJAVA 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.

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Intrinsic Data TypesIntrinsic Data Types2. byte:

- a 1 byte integer, capable of representing numbers from numbers from -128 to +127. 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.

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Intrinsic Data TypesIntrinsic Data Types4. 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.

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Intrinsic Data TypesIntrinsic Data Types6. 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.

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Intrinsic Data TypesIntrinsic Data Types

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

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Key JAVA OperatorsKey JAVA OperatorsOperator

Description

Example

( )

Parenthesis

(X+2)/3

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Description

Example

*

Multiply

X*2

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Description

Example

/

Divide

X/12

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Description

Example

%

Modulus

7%3

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Description

Example

+

Add

X+7

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Description

Example

-

Subtract

X-6

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Description

Example

>

Greater than

X>3

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Description

Example

<

Less than

X<3

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Description

Example

>=

Greater than or equal

X>=3

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Description

Example

<=

Less than or equal

X<=3

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Description

Example

==

Equals

X==3

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Description

Example

!=

Not equal

X!=3

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Description

Example

=

Assignment operator

Y=X+3

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The Body Mass Index CalculatorThe 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

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The Body Mass Index CalculatorThe Body Mass Index Calculator

Three versions

– Input/Output using the command prompt

– Input/Output using dialog boxes

– Web environments use an applet interface

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(b) console application using dialog boxes

(a) console application in a command prompt window

(c) applet

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

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Design the SolutionDesign the SolutionDesign the three kinds of user interfaces

with storyboardsDesign the logic of the program

– Use pseudocode for sequential flow for all programs

– Use an event diagram for the appletValidate the design

– Compare the program design with the original requirements

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Coding the ProgramCoding the ProgramImport 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

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Coding the ProgramCoding the Program

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Storing DataStoring DataJava 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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Declaring VariablesDeclaring Variables

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User Input – Streams and the System User Input – Streams and the System ClassClass 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

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User Input – Streams and the System User Input – Streams and the System ClassClass 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

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Using the BufferedReader classUsing 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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User Prompts, Inputs, User Prompts, Inputs, and Conversionsand 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);

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Assignment StatementsAssignment StatementsGeneral syntax: location = value

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Arithmetic OperatorsArithmetic Operators

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Arithmetic OperatorsArithmetic 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

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Comparison OperatorsComparison Operators A comparison operation results in a true or false

value that can be stored in a boolean variable

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Numeric ExpressionsNumeric 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

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Conditional ExpressionsConditional 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 (==, !=)

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Parentheses in ExpressionsParentheses 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

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Construction of Error-Free Construction of Error-Free ExpressionsExpressions 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

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The Math ClassThe Math Class

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Using Variables in OutputUsing Variables in Output

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Compiling, Running, and Compiling, Running, and Documenting the ApplicationDocumenting the ApplicationCompile the Body Mass Index

Calculator programExecute the programTest the program by entering the

sample input data supplied in the requirements phase at the prompts

Verify the resultsPrint the source code and screen

images for documentation

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Using Swing ComponentsUsing Swing ComponentsSave the previous version of the Body

Mass Index Calculator with a new filenameImport 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

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Swing Dialog BoxesSwing Dialog Boxes Dialog boxes are created with the JOptionPane

“show” methods The showInputDialog() and showConfirmDialog

return a String containing the user input

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Swing Dialog BoxesSwing Dialog Boxes

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Closing Programs that use SwingClosing Programs that use SwingSystem.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

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Saving, Compiling, and Running the Saving, Compiling, and Running the Swing VersionSwing VersionVerify that the file name matches the

class name at the beginning of the codeCompile the source codeTest with the same sample data for all

versions to compare output resultsIf incorrect or unrealistic data is entered

by the user, errors will occur– Errors and exception handling will be

discussed in a later chapter

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Moving to the Web 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

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Moving to the WebMoving to the Web Every event class has one or more

associated listener interfaces

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Moving to the WebMoving to the Web

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Adding Interface Components Adding Interface Components to an Appletto 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

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

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The actionPerformed() MethodThe 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()

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

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Creating an HTML Host Document Creating an HTML Host Document for an Interactive Appletfor an Interactive AppletCompile the appletWrite an HTML Host Document to

execute the applet– Use the <APPLET> 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

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File ManagementFile 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

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Conclusion Conclusion of Class 4of Class 4

Documents

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