Transcript ppt - AD Book Enterprises

9/7: Variable Types, Arithmetic
Operators, Comparison Operators
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•
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Addition.java in depth
Variable types & data types
Input from user: how to get it
Arithmetic operators
Addition.java
import
statement
class
import javax.swing.JOptionPane;
header
method
header public class Addition {
public static void main ( String args[] )
declaring {
variables:
String firstNumber, secondNumber;
Strings
int number1, number2, sum;
& ints
firstNumber = JOptionPane.showInputDialog ( "Enter a number" );
secondNumber = JOptionPane.showInputDialog ( "And another" );
number1 = Integer.parseInt ( firstNumber );
number2 = Integer.parseInt ( secondNumber );
sum = number1 + number2;
JOptionPane.showMessageDialog ( null, "The sum is " +
sum, "Results", JOptionPane.PLAIN_MESSAGE );
System.exit ( 0 );
}
}
Variables & Data Types
• String – a series of characters.
– EX: Ann , 1450 , var30 , g , YES
– to declare a String variable, put the variable type
String before the name of the variable.
String firstNumber ;
– to declare more than one String variable at the same
time, separate the variable names with commas.
String firstNumber , secondNumber ;
• A declaration is a statement – must end with a
semicolon.
Variables & Data Types
• int – an integer-type number.
– EX: 45 , -1001 , 3 , 58692
– to declare an int variable, put the variable type int
before the name of the variable.
int number1 ;
– to declare more than one int variable at the same
time, separate the variable names with commas.
int number1 , number2 ;
– other number formats: float , double , long , short
Addition.java
import javax.swing.JOptionPane;
public class Addition {
public static void main ( String args[] )
{
String firstNumber, secondNumber;
initializing
int number1, number2, sum;
firstNumber &
secondNumber firstNumber = JOptionPane.showInputDialog ( "Enter a number" );
secondNumber = JOptionPane.showInputDialog ( "And another" );
number1 = Integer.parseInt ( firstNumber );
number2 = Integer.parseInt ( secondNumber );
sum = number1 + number2;
JOptionPane.showMessageDialog ( null, "The sum is " +
sum, "Results", JOptionPane.PLAIN_MESSAGE );
System.exit ( 0 );
}
}
Inputs: How we did it.
• We initialized (gave an initial value to)
firstNumber & secondNumber by the lines
firstNumber = JOptionPane.showInputDialog ( "Enter a number" );
secondNumber = JOptionPane.showInputDialog ( "And another" );
• JOptionPane.showInputDialog panes accept
String type inputs. Even if it looks like a
number, Java sees it as a String.
Addition.java
import javax.swing.JOptionPane;
public class Addition {
public static void main ( String args[] )
{
String firstNumber, secondNumber;
int number1, number2, sum;
firstNumber = JOptionPane.showInputDialog ( "Enter a number" );
secondNumber = JOptionPane.showInputDialog ( "And another" );
initializing
number1 &
number2
number1 = Integer.parseInt ( firstNumber );
number2 = Integer.parseInt ( secondNumber );
sum = number1 + number2;
JOptionPane.showMessageDialog ( null, "The sum is " +
sum, "Results", JOptionPane.PLAIN_MESSAGE );
System.exit ( 0 );
}
}
Inputs: How we did it.
• We then initialized (gave an initial value to)
number1 & number2 by the lines
number1 = Integer.parseInt ( firstNumber );
number2 = Integer.parseInt ( secondNumber );
• These lines convert the String values of
firstNumber and secondNumber into int
values and store them as number1 and
number2.
Addition.java
import javax.swing.JOptionPane;
public class Addition {
public static void main ( String args[] )
{
String firstNumber, secondNumber;
int number1, number2, sum;
firstNumber = JOptionPane.showInputDialog ( "Enter a number" );
secondNumber = JOptionPane.showInputDialog ( "And another" );
number1 = Integer.parseInt ( firstNumber );
number2 = Integer.parseInt ( secondNumber );
initializing
sum
sum = number1 + number2;
JOptionPane.showMessageDialog ( null, "The sum is " +
sum, "Results", JOptionPane.PLAIN_MESSAGE );
System.exit ( 0 );
}
}
Arithmetic Operators
Java operator Arithmetic
operator
Addition
+
Algebraic
expression
Java
expression
f+7
f+7
Subtraction
-
p–c
p–c
Multiplication
*
pv
p*v
Division
/
x/y
x/y
Modulus
%
r mod s
r%s
Order of Operation
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Just like algebra
inside parentheses first
multiplication, division, & modulus next
addition & subtraction last
left to right
• EX: 2 * 4 + 3 % 2 - (4 / 2 + 5 ) = ?
Order of Operation Example
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2 * 4 + 3 % 2 - (4 / 2 + 5 ) = ?
2*4+3%2-(2+5)=?
2*4+3%2-(2+5)=?
2*4+3%2-( 7 )=?
2*4+3%2-( 7 )=?
8+ 3%2-( 7 )=?
8+ 3%2-( 7 )=?
8+
1 -( 7 )=?
8+
1 - 7
=2
1st Program of the Day: pg. 58
• Pg. 58: Comparison.java
– Pay attention to the comparison operators (<, >=, etc.)
• Second Half:
– Comparison.java in depth:
– the if structure
– comparison operators
– assigning new values to an old variable.
Part 2: Comparison Operators
• Comparison.java
• Using the if structure
• Equality operators
• Relational operators
import
statement
Comparison.java
import javax.swing.JOptionPane;
class
header
method
header public class Comparison {
public static void main( String args[] )
declaring {
variables:
String firstNumber, secondNumber, result;
Strings
int number1, number2;
& ints
initializing
firstNumber &
secondNumber firstNumber = JOptionPane.showInputDialog( "Enter first int.:" );
secondNumber = JOptionPane.showInputDialog( "Enter 2nd int:" );
initializing
number1 &
number2
number1 = Integer.parseInt( firstNumber );
number2 = Integer.parseInt( secondNumber );
initializing
result
result = "";
Comparison.java (pt. 2)
if ( number1 == number2 )
result = number1 + " == " + number2;
if ( number1 != number2 )
result = number1 + " != " + number2;
“If number1 is equal to
number2, then set
result to be number1
plus a double equal sign
plus number2.”
if ( number1 < number2 )
result = result + "\n" + number1 + " < " + number2;
if ( number1 > number2 )
result = result + "\n" + number1 + " > " + number2;
if ( number1 <= number2 )
result = result + "\n" + number1 + " <= " + number2;
if ( number1 >= number2 )
result = result + "\n" + number1 + " >= " + number2;
The if structure
Use the if structure to have statements execute
ONLY under certain conditions.
if ( condition )
rest of statement ;
Note that the if ( condition ) is not a statement by
itself ( just like English ).
The spacing and line structure is good practice.
Comparison.java (pt. 2)
if ( number1 == number2 )
result = number1 + " == " + number2;
if ( number1 != number2 )
result = number1 + " != " + number2;
“If number1 is less than
number2, set result to be
itself plus a new line escape
sequence plus number1
plus a ‘less than’ sign plus
number2.”
if ( number1 < number2 )
result = result + "\n" + number1 + " < " + number2;
if ( number1 > number2 )
result = result + "\n" + number1 + " > " + number2;
if ( number1 <= number2 )
result = result + "\n" + number1 + " <= " + number2;
if ( number1 >= number2 )
result = result + "\n" + number1 + " >= " + number2;
Equality & Relational Operators
• To compare values.
• Equality operators: Equal to, not equal to
• Relational operators: Greater than, less than
Equality Operators
English
phrase
Algebraic
Equality
Operator
Java
equality
operator
Example of
Java condition
x is equal
to y
=
==
x == y
x is not
equal to y
=
!=
x != y
Relational Operators
English
phrase
Algebraic
Relational
Operator
Java
Example of
relational Java condition
operator
x is greater
than y
>
>
x > y
x is less
than y
<
<
x < y
x is greater
or equal to
y
x is less
than or
equal to y
>
>=
x >= y
<
<=
x <= y
Comparison.java (pt. 3)
JOptionPane.showMessageDialog( null, result, "Comparison
Results", JOptionPane.INFORMATION_MESSAGE );
System.exit( 0 );
}
}
result, whatever it is after
executing the if statements,
is put in the main body of
the MessageDialog box.
Program of the Day
• Problem 2.17 (pg. 73): write a program
• Work in pairs
• Use Comparison.java as a help/template in
creating the program