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Fundamental concepts
in Java
Lesson plan
• Variable declaration, assign statement &
practice
• Design document & practice
Numeric data
Variable declaration:
<data type> <variable_name>;
If more than one variable has the same
data type:
<data type> <name1>, <name2>..;
/**
* Sample program …
**/
import javax.swing.*;
import java.text.*;
Variable
Declaration
public class LoanCalculator{
public static void main(String[] args) {
double loanAmount; // represents the amount being borrowed
double annualInterestRate; // represents the interest rate annually
double monthlyPayment; // represents the amount of money one has to
double totalPayment; // represents the amount of money one has to pay
int loanPeriod; // represents the number of years of the loan
String inputStr; // is a place holder to get input value from a user
…..
Six numerical data types
•
•
•
•
•
•
byte: -128 to 127
short:-32768 to 32767 (-215 to 215-1)
int: -231 to 231-1
long: -263 to 263-1
float: -3.4E+38 to 3.4E+38
double:-1.797E+308 to 1.797E+308
Assignment statement
<variable name> = <expression>;
Example:
x =2*5+6-1;
Variable names
• It must be a legal identifier.
• It must not be a keyword, a boolean
literal (true or false), or the reserved
word null.
• It must be unique within its scope.
Variable name (cont.)
• Legal identifier:be composed of letters,
numbers, _ and $. Identifiers may only begin
with a letter, _, or $.
• Keyword:
http://java.sun.com/docs/books/tutorial/java/nu
tsandbolts/_keywords.html
• Variable names begin with a lowercase letter
• Class names begin with an uppercase letter
Arithmetic Expression
• Any expression involving numerical value
is called arithmetic expression
For example:
x+15
y /16
Arithmetic operators
• Addition: +
x+y
• Subtraction: x-y
• Multiplication: *
x*y
• Division: /
x/y
• Modulo: %
x%y
Constant
/**
* Sample program …
**/
import javax.swing.*;
import java.text.*;
public class LoanCalculator{
public static void main(String[] args) {
final int MONTHS_IN_YEAR = 12;
// double loanAmount; // represents the amount being ..
int loanPeriod; // represents the number of years of the loan
String inputStr;
…..
inputStr = JOptionPane.showInputDialog(null,"Loan Amount
(dollars.cents):");
Constant and variables
• Constant:
– Value it contains doesn’t change
final int MONTHS_IN_YEAR = 12;
• Variables:
– Value it contains may vary
double loanAmount;
• loanAmount =0;
• loanAmount = 1000.99;
Formula representation
• X = 10
• Y=5
What are the values of:
sum = x+y
difference = x-y
product = x*y
quotient = x/y
remainder = x%y
24= Math.pow(2,4)
Practice
import javax.swing.*;
import java.text.*;
public class PrintProduct{
public static void main(String[] args) {
double first Number; // invalid variable name, space is in between
double 12_second%Number; //start with a number, % is not allowed
double _13_thirdNumber; //OK
double $product; // OK
firstNumber=10.12; //
12_second%Number=12.6;
product== first Number * 12_second%Number; //invalid assignment
}
}
Integer division and type casting
• Integer division:
– Integer/integer = integer, 7/2 = 3
– Integer/double = double, 7/2.0 = 3.5
– Double/integer = double, 7.0/2 = 3.5
• Type casting: a process that converts a value of
one data type to another data type.
Implicit casting
Explicit casting
Type casting (cont.)
• Implicit casting:
– Operand is converted from a lower to a
higher precision
– Higher precision: a data type with a larger
range of values
• Double has a higher precision than float
• Int has a higher precision than short
– Operand: can be a constant, variable,
method call or another arithmetic expression
Type casting (cont.)
• Explicit casting
– (<data type>) <expression>
– Example:
float result;
result = (float) ((3+5)/6);
and
result = ((float) (5+3))/6;
More formula representation
• xn
– Math.pow(x,n)
How about: (1+i)n
– Math.pow((1+i),n)
More formula representation
How about:


i
P V
n 
1  (1  i) 
P=V*(i/(1-(Math.pow(1+i,-n))))
LoanCalculator.java
• Steps:
– Describe the program/problem (optional)
– Get input from users
– Computation (compute monthly payment
and total payment)
– Display the results to users
Get input values from users
• Example:
inputStr = JOptionPane.showInputDialog(null,”<message>”);
If variable has double data type:
<variable_name> = Double.parseDouble(inputStr);
If variable has integer data type:
<variable_name> = Integer.parseInt(inputStr);
Get input values from users
Using System.in:
import java.io.*;
try {
InputStreamReader in = new InputStreamReader( System.in );
BufferedReader stdin = new BufferedReader( in );
System.out.print( "Loan amount (dollars.cents: " );
inputStr = stdin.readLine();
} catch(IOException e) {
System.out.println("Error in reading a user's input");
System.exit(-1);
}
loanAmount = Double.parseDouble(inputStr);
• …..
Display results to users
• System.out.println(“message :”+<variable name>);
Example:
System.out.println("Loan Amount: $"+ loanAmount);
System.out.println("Annual Interest Rate: "+
annualInterestRate +"%");
Design
• Identify classes based on naming
convention:
– Class name starts with Capital letter
Design
Class
LoanCalculator
JOptionPane
Purpose
-What is it?
Example: The main class
of the program
-What does it do?
It computes the monthly
payment and total
payment for a loan
-What is it? Java library
-What does it do?
It displays a dialog box to
get inputs from a user
Design
String
- What is it? Java library
- What does it do?
String manipulation, represents
a place holder for storing a
user’s inputs
DecimalFormat
- What is it? Java library
- What does it do?
Use to format numbers
Design
String
-What is it? Java library
-What does it do?
String manipulation, represents
a place holder for storing a
user’s inputs
DecimalFormat
-What is it? Java library
-What does it do?
Use to format numbers
Design
Double
-What is it? Java library
-What does it do
Represent double data type as an
object
Integer
-What is it? Java library
-What does it do?
Represent integer data type as an
object
Design
Math
-What is it? Java library
-What does it do?
Perform numeric operations
System
-What is it? Java library
-What does it do?
Print a message to the screen and
exit the program
Design
JOptionPane
System
DecimalFormat
LoanCalculator
String
Integer
Double
Math