The document provides an overview of Java's Scanner and JOptionPane classes for reading keyboard input and displaying dialog boxes. It discusses various methods for input retrieval and type conversion, as well as decision structures like if-else statements and switch statements to control program flow. Additionally, it outlines the syntax and examples for using these features effectively.

1. MMIIDDTTEERRMM CCOOVVEERRAAGGEE
READING KEYBOARD
OUTPUT

2. SSCCAANNNNEERR CCLLAASSSS((RREEFFRREESSHH))
Ex.
Scanner keyboard = new Scanner(System.in)
Declares a
variable
named
keyboard
Creates a Scanner
object in
memory. Read
input from
System.in

3. SSCCAANNNNEERR CCLLAASSSS((MMeetthhooddss))
STRING
Bytes
Integers
Long integers
Short integers
Float
Doubles

4. SSCCAANNNNEERR CCLLAASSSS((MMeetthhooddss))
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.

5. SSCCAANNNNEERR CCLLAASSSS((MMeetthhooddss))
 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.

6. SSCCAANNNNEERR CCLLAASSSS((MMeetthhooddss))
EXAMPLE IMPLEMENTATION
Payroll.java

7. DDIIAALLOOGG BBOOXXEESS
CONCEPT:
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.

8. DDIIAALLOOGG BBOOXXEESS
Types 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.

9. DDIIAALLOOGG BBOOXXEESS
Beginning 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.

10. MMeessssaaggee DDiiaallooggss
 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.

11. IINNPPUUTT DDIIAALLOOGGSS
 showInputDialog method – to display an input
dialog in JOptionPane class.
Statement to call the method:
String name;
name = JOptionPane.showInputDialog(“Enter your name.”);

12. SSaammppllee CCooddee
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.
} }

13. DDiissaaddvvaannttaaggee ooff JJOOppttiioonnPPaannee
JOptionPane 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.

14. Methods ffoorr ccoonnvveerrttiinngg ssttrriinnggss ttoo nnuummbbeerrss
Byte.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.

15. SSaammppllee UUssaaggee
 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.

16. DDEECCIISSIIOONN // CCOONNTTRROOLL
FFLLOOWW SSTTRRUUCCTTUURREESS

17. IIFF SSTTAATTEEMMEENNTT
CONCEPT:
> 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

18. IIFF SSTTAATTEEMMEENNTT SSYYNNTTAAXX
If (BooleanExpression)
statement;
BooleanExpression- appears inside the
parentheses must be a boolean
expression.
If the boolean expression is true, the next
statement is executed.

19. FFllooww ooff IIff ssttaatteemmeennttss

20. SSAAMMPPLLEE UUSSAAGGEE
PROBLEM:
If the value is less than 32, displays the
message “Invalid Number”
CODE:
if ( value < 32)
System.out.println(“Invalid Number”);

21. IIff--eellssee SSttaatteemmeenntt
Concept:
> 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.

22. IIff ––eellssee ssttaatteemmeenntt SSYYNNTTAAXX
if(BooleanExpression){
statement;
} else {
statement;
}

23. LLooggiicc ooff iiff--eellssee SSttaatteemmeenntt

24. NNEESSTTEEDD IIFF SSTTAATTEEMMEENNTT
CONCEPT:
> To test more than one
condition, an if statement can
be nested inside another if
statement.

25. NNeesstteedd iiff ssttaatteemmeenntt SSYYNNTTAAXX
if (BooleanExpression)
{
if(BooleanExpression)
{
statement;
}
else
{
statement;
}
else
{
statement;
}

26. TTHHEE iiff--eellssee--iiff SSttaatteemmeenntt
CONCEPT:
 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.

27. SSyynnttaaxx ooff iiff--eellssee--iiff SSttaatteemmeenntt
if(BooleanExpression){
statement;
}
else if(BooleanExpression){
statement;
}
else{
statement;
}
main test
Alternative
test if the if
statement is
false

28. LLOOGGIICCAALL OOPPEERRAATTOORRSS
Java 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.

29. TTrruutthh ttaabbllee ooff tthhee &&&& ooppeerraattoorr
EXPRESSION VALUE
true&&false false
false&&true false
false&&false false
true&&true true

30. TTrruutthh ttaabbllee ooff tthhee |||| ooppeerraattoorr
EXPRESSION VALUE
true|| false true
false|| true true
false|| false false
true|| true true

31. LLOOGGIICCAALL OOPPEERRAATTOORRSS IINN OORRDDEERR OOFF
PPRREECCEEDDEENNCCEE
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.

32. EExxaammppllee UUssaaggee
Assume x is an int w/ a value stored in it:
! (x >2)
read as “ is x not greater than 2?”
!x>2
read as “ is logical complement of x is
greater than 2? ”
Note: ! operator can be applied only to boolean
expressions.

33. SSwwiittcchh SSttaatteemmeenntt
CONCEPT:
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.

34. SSttrruuccttuurree

35. SSwwiittcchh ssttaatteemmeenntt ssyynnttaaxx
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.

36. SSaammppllee UUssaaggee((fflloowwcchhaarrtt eexxaammppllee))
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;
}