Reading Keyboard Output

MIDTERM MIDTERM COVERAGECOVERAGE

READING KEYBOARD OUTPUT

SCANNER SCANNER CLASS(CLASS(REFRESHREFRESH))Ex. Scanner keyboard = new Scanner(System.in)

Declares a variable named keyboard

Creates a Scanner object in memory. Read input from System.in

SCANNER SCANNER CLASS(CLASS(MethodsMethods))STRINGBytesIntegersLong integersShort integersFloatDoubles

SCANNER SCANNER CLASS(CLASS(MethodsMethods))For example: int number; Scanner keyboard= new

Scanner(System.in);System.out.print(“Enter an integer value”); number= keyboard.nextInt();

Therefore, this statement formats the input that was entered @ the keyboard as an int.

SCANNER SCANNER CLASS(CLASS(MethodsMethods)) nextByte – returns input as Byte nextDouble – returns input as

Double. nextFloat – returns input as Float nextInt – returns input as an Int nextLine – return input as String. nextLong – return input as a long next Short – return input as a

short.

SCANNER SCANNER CLASS(CLASS(MethodsMethods))

EXAMPLE IMPLEMENTATION

Payroll.java

DIALOG BOXESDIALOG BOXESCONCEPT:

JOptionPane class allows a user to display a Dialog Box.

Dialog Box – is a small graphical window that displays a message to the user or request input. We can quickly display dialog boxes w/ JOptionPane class.

DIALOG BOXESDIALOG BOXESTypes of DIALOG BOXES

Message Dialog – a dialog box that displays a message; an OK button is also displayed.

Input Dialog – dialog box tat prompts the user for input & provides text field where input is typed; an OK button and a CANCEL button are also displayed.

DIALOG BOXESDIALOG BOXESBeginning Statement in your

code when using JoptionPane: import javax. swing.JOptionPane;

Purpose: this statement tells the compiler where to find the JOptionPane class, and make it available to your program.

Message DialogsMessage Dialogs showMessageDialog method- is used

to display a message dialog box.Statement to call the method: JOptionPane.showMessageDialog (null, “HELLO

WORLD”);

ARGUMENT PURPOSE: null – causes the dialog box to be displayed in the

center of the screen.HELLO WORLD – the message we want to display in

the dialog box.

INPUT DIALOGSINPUT DIALOGS showInputDialog method – to display

an input dialog in JOptionPane class.

Statement to call the method: String name; name = JOptionPane.showInputDialog(“Enter

your name.”);

Sample CodeSample Code import javax.swing.JOptionPane;

public class Names {

public static void main (String [ ] args)

{

firstName= JOptionPane.showInputDialog(“What’s your firstname”);

middleName=JOptionPane.showInputDialog(“What’s your middle name”);

lastName=JOptionPane.showInputDialog(“What’s your Last Name”);

JOptionPane.showMessageDialog(null, “HELLO” +firstName + “ “ + middleName + “ “ + lastName);

System.exit (0); This statement causes the program to end, & is

required if we use the JOptionPane class to display dialog

box.

} }

Disadvantage of JOptionPaneDisadvantage of JOptionPaneJOptionPane class does not have

different methods for reading values of different data types as input.

showInputDialog method always returns the user’s input as a String.

Problem when use in Math operation.Because we cannot perform math on

strings.In such case, you must convert the

input to a numeric value.

Methods for converting strings to Methods for converting strings to numbersnumbersByte.parseByte – method to convert string to

a byte.Double.parseDouble – method to convert

string to a double.Float.parseFloat – method to convert string to

a float.Integer.parseInt – method to convert string to

an int.Long.parseLong – method to convert string to

a long.Short.parseShort – method to convert string

to a short.

Sample UsageSample Usage int num;

String str;str=JOptionPane.showInputDialog(“Enter a number”);

num= Integer.parseInt(str);

num variable will hold the value entered by the user, converted to an int.

DECISION / DECISION / CONTROL FLOW CONTROL FLOW

STRUCTURESSTRUCTURES

IF STATEMENTIF STATEMENTCONCEPT:

> is used to create decision structures, which allow the program to have more than one path of execution> causes one or more statements to execute only when boolean expression is true.

NOTE: RELATIONAL OPERATIONS ARE USED

IF STATEMENT SYNTAXIF STATEMENT SYNTAX

If (BooleanExpression)statement;

BooleanExpression- appears inside the parentheses must be a boolean expression.

If the boolean expression is true, the next statement is executed.

Flow of If statementsFlow of If statements

SAMPLE USAGESAMPLE USAGEPROBLEM:

If the value is less than 32, displays the message “Invalid Number”

CODE: if ( value < 32)

System.out.println(“Invalid Number”);

If-else StatementIf-else StatementConcept:

> will execute one group of statements if its BOOLEAN EXPRESSION is True, or another group if its BOOLEAN EXPRESSION is False.

> expansion of the if statement.

If –else statement SYNTAXIf –else statement SYNTAX

if(BooleanExpression){

statement; } else {

statement; }

Logic of if-else StatementLogic of if-else Statement

NESTED IF STATEMENTNESTED IF STATEMENT

CONCEPT:

> To test more than one condition, an if statement can be nested inside another if statement.

Nested if statement Nested if statement SYNTAXSYNTAX

if (BooleanExpression)

{

if(BooleanExpression)

{

statement;

}

else

{

statement;

}

else

{

statement;

}

THE if-else-if StatementTHE if-else-if StatementCONCEPT: if-else-if statement test a series of conditions than with a set of nested if-else statement.

else-if statement is in between the if & else statement.

Syntax of if-else-if Syntax of if-else-if StatementStatement

if(BooleanExpression){statement;

} else if(BooleanExpression){

statement;} else{

statement;}

main test

Alternative test if the if statement is false

LOGICAL OPERATORSLOGICAL OPERATORSJava provides two binary operators, && and ||, which are used to combine two boolean expressions into a single expression.

Java also provides the unary ! operator, which reverses the truth of a boolean expression.

Truth table of the && Truth table of the && operatoroperator

EXPRESSION VALUE true&&false false false&&true false false&&false false true&&true true

Truth table of the || Truth table of the || operatoroperator

EXPRESSION VALUE true|| false true false|| true true false|| false false true|| true true

LOGICAL OPERATORS IN ORDER LOGICAL OPERATORS IN ORDER OF PRECEDENCEOF PRECEDENCE

1st = !2nd=&&3rd= ||Note: ! Operator has higher precedence

than many of Java’s other operators.You should enclose its operand in ()

unless you intend to apply it to a variable or simple expression w/ no other operators.

Example UsageExample Usage

Assume x is an int w/ a value stored in it:

! (x >2) read as “ is x not greater than 2?”

!x>2read as “ is logical complement of x is greater than 2? ”

Note: ! operator can be applied only to boolean expressions.

Switch StatementSwitch StatementCONCEPT:

switch statement lets the value of a variable or expression determine where the program will branch to.

is a multiple alternative decision structure.

can be used as an alternative of if-else-if statement that test the same variable w/ several different values.

StructureStructure

Switch statement syntaxSwitch statement syntax switch(variable) {

case value_1:statement;break;

case value_N : statement;break;

default :statement;break;

}

These statement is executed if the variable is equal to value_1

These statement is executed if the variable is equal to value_N.

These statement is executed if the variable is not equal to any of the case values.

Sample Usage(flowchart Sample Usage(flowchart example)example) switch(month)

{

case 1:

System.out.print(“January”);

break;

case 2:

System.out.print(“February”);

break;

case 3:

System.out.print(“March”);

break;

default:

System.out.print(“Error:”);

break;

}