CS1101X: Programming Methodology Recitation 1 Java Basics Numerical Data

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CS1101X Programming MethodologyRecitation 1
Java Basics Numerical Data
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Problem Statement

• Problem statement
• Write a program that asks for the users first,
  middle, and last names and replies with their
  initials.

Example input Andrew Lloyd Weber output
ALW
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Overall Plan

• Identify the major tasks the program has to
  perform.
• We need to know what to develop before we
  develop!
• Tasks
• Get the users first, middle, and last names
• Extract the initials and create the monogram
• Output the monogram

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Development Steps

• We will develop this program in two steps
• Start with the program template and add code to
  get input
• Add code to compute and display the monogram

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Step 1 Design

• The program specification states get the users
  name but doesnt say how.
• We will consider how in the Step 1 design
• We will use JOptionPane for input
• Input Style Choice 1
• Input first, middle, and last names separately
• Input Style Choice 2
• Input the full name at once
• We choose Style 2 because it is easier and
  quicker for the user to enter the information

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Step 1 Code
/ Chapter 2 Sample Program Displays the
Monogram File Step1/Ch2Monogram.java / import
javax.swing. class Ch2Monogram public
static void main (String args) String
name name JOptionPane.showInputDialog(null,
"Enter your full name (first, middle,
last)") JOptionPane.showMessageDialog(null,
name)
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Step 1 Test

• In the testing phase, we run the program and
  verify that
• we can enter the name
• the name we enter is displayed correctly

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Step 2 Design (1/2)

• Our programming skills are limited, so we will
  make the following assumptions
• input string contains first, middle, and last
  names
• first, middle, and last names are separated by
  single blank spaces
• Examples
• John Quincy Adams (okay)
• John Kennedy (not okay)
• Harrison, William Henry (not okay)

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Step 2 Design (2/2)

• Given the valid input, we can compute the
  monogram by
• breaking the input name into first, middle, and
  last
• extracting the first character from them
• concatenating three first characters

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Step 2 Code (1/2)
/ Chapter 2 Sample Program Displays the
Monogram File Step 2/Ch2MonogramStep2.java / im
port javax.swing. class Ch2Monogram public
static void main (String args) String
name, first, middle, last, space,
monogram space " " //Input the full
name name JOptionPane.showInputDialog(null,
"Enter your full name (first, middle,
last)" )
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Step 2 Code (2/2)
//Extract first, middle, and last names first
name.substring(0, name.indexOf(space)) name
name.substring(name.indexOf(space)1,
name.length()) middle
name.substring(0, name.indexOf(space)) last
name.substring(name.indexOf(space)1,
name.length()) //Compute the
monogram monogram first.substring(0, 1)
middle.substring(0, 1) last.substri
ng(0,1) //Output the result JOptionPane.showM
essageDialog(null, "Your monogram is "
monogram)
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Step 2 Test

• In the testing phase, we run the program and
  verify that, for all valid input values, correct
  monograms are displayed.
• We run the program numerous times. Seeing one
  correct answer is not enough. We have to try out
  many different types of (valid) input values.

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Program Review

• The work of a programmer is not done yet.
• Once the working program is developed, we perform
  a critical review and see if there are any
  missing features or possible improvements
• One suggestion
• Improve the initial prompt so the user knows the
  valid input format requires single spaces between
  the first, middle, and last names

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Problem Statement

• Problem statement
• Write a loan calculator program that computes
  both monthly and total payments for a given loan
  amount, annual interest rate, and loan period.

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Overall Plan

• Tasks
• Get three input values loanAmount, interestRate,
  and loanPeriod.
• Compute the monthly and total payments.
• Output the results.

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Required Classes
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Development Steps

• We will develop this program in four steps
• Start with code to accept three input values.
• Add code to output the results.
• Add code to compute the monthly and total
  payments.
• Update or modify code and tie up any loose ends.

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Step 1 Design

• Call the showInputDialog method to accept three
  input values
• loan amount,
• annual interest rate,
• loan period.
• Data types are

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Step 1 Code (1/2)
Directory Chapter3/Step1 Source File
Ch3LoanCalculator.java
Program source file is too big to list here. From
now on, we ask you to view the source files using
your Java IDE.
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Step 1 Code (2/2)
import javax.swing. class Ch3LoanCalculator
public static void main (String args)
double loanAmount, annualInterestRate
int loanPeriod String
inputStr //get input values
inputStr JOptionPane.showInputDialog(n
ull, "Loan
Amount (DollarsCents)") loanAmount
Double.parseDouble(inputStr)
inputStr JOptionPane.showInputDialog(n
ull, "Annual
Interest Rate (e.g., 9.5)")
annualInterestRate Double.parseDouble(inputStr)
inputStr JOptionPane.showInpu
tDialog(null,
"Loan Period - of years") loanPeriod
Integer.parseInt(inputStr)
//echo print the input values
System.out.println("Loan Amount "
loanAmount) System.out.println("Annual
Interest Rate " annualInterestRate "")
System.out.println("Loan Period (years) "
loanPeriod)
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Step 1 Test

• In the testing phase, we run the program multiple
  times and verify that
• we can enter three input values
• we see the entered values echo-printed correctly
  on the standard output window

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Step 2 Design

• We will consider the display format for out.
• Two possibilities are (among many others)

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Step 2 Code (1/3)
Directory Chapter3/Step2 Source File
Ch3LoanCalculator.java
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Step 2 Code (2/3)
import javax.swing. class Ch3LoanCalculator
public static void main (String args)
double loanAmount, annualInterestRate
double monthlyPayment, totalPayment
int loanPeriod String inputStr
//get input values inputStr
JOptionPane.showInputDialog(null,
"Loan Amount
(DollarsCents)") loanAmount
Double.parseDouble(inputStr) inputStr
JOptionPane.showInputDialog(null,
"Annual Interest
Rate (e.g., 9.5)") annualInterestRate
Double.parseDouble(inputStr) inputStr
JOptionPane.showInputDialog(null,
"Loan Period - of
years") loanPeriod
Integer.parseInt(inputStr)
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Step 2 Code (3/3)
//compute the monthly and total
payments monthlyPayment 132.15
totalPayment 15858.10 //display the
result System.out.println("Loan Amount
" loanAmount)
System.out.println("Annual Interest Rate "
annualInterestRate "")
System.out.println("Loan Period (years) "
loanPeriod) System.out.println("\n")
//skip two lines System.out.println("Month
ly payment is " monthlyPayment)
System.out.println(" TOTAL payment is "
totalPayment)
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Step 2 Test

• We run the program numerous times with different
  types of input values and check the output
  display format.
• Adjust the formatting as appropriate

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Step 3 Design

• The formula to compute the geometric progression
  is the one we can use to compute the monthly
  payment.
• The formula requires the loan period in months
  and interest rate as monthly interest rate.
• So we must convert the annual interest rate
  (input value) to a monthly interest rate (per the
  formula), and the loan period to the number of
  monthly payments.

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Step 3 Code (1/3)
Directory Chapter3/Step3 Source File
Ch3LoanCalculator.java
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Step 3 Code (2/3)
import javax.swing. class Ch3LoanCalculator
public static void main (String args)
final int MONTHS_IN_YEAR 12
double loanAmount, annualInterestRate
double monthlyPayment, totalPayment,
monthlyInterestRate int loanPeriod,
numberOfPayments String inputStr
//get input values inputStr
JOptionPane.showInputDialog(null,
"Loan Amount
(DollarsCents)") loanAmount
Double.parseDouble(inputStr) inputStr
JOptionPane.showInputDialog(null,
"Annual Interest
Rate (e.g., 9.5)") annualInterestRate
Double.parseDouble(inputStr) inputStr
JOptionPane.showInputDialog(null,
"Loan Period - of
years") loanPeriod
Integer.parseInt(inputStr)
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Step 3 Code (3/3)
//compute the monthly and total
payments monthlyInterestRate
annualInterestRate / MONTHS_IN_YEAR / 100
numberOfPayments loanPeriod
MONTHS_IN_YEAR monthlyPayment
(loanAmount monthlyInterestRate) /
(1 - Math.pow(1/(1
monthlyInterestRate),
numberOfPayments ) )
totalPayment monthlyPayment
numberOfPayments //display the result
System.out.println("Loan Amount
" loanAmount) System.out.println("Annu
al Interest Rate " annualInterestRate
"") System.out.println("Loan Period
(years) " loanPeriod)
System.out.println("\n") //skip two lines
System.out.println("Monthly payment is "
monthlyPayment) System.out.println("
TOTAL payment is " totalPayment)
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Step 3 Test

• We run the program numerous times with different
  types of input values and check the results.

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Step 4 Finalize

• We will add a program description
• We will format the monthly and total payments to
  two decimal places using DecimalFormat.
• Directory Chapter3/Step4
• Source File Ch3LoanCalculator.java

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Step 4 Code (1/3)
import javax.swing. import java.text. class
Ch3LoanCalculator public static void main
(String args) final int
MONTHS_IN_YEAR 12 double loanAmount,
annualInterestRate,
monthlyPayment, totalPayment,
monthlyInterestRate int loanPeriod,
numberOfPayments String inputStr
DecimalFormat df new DecimalFormat("0.00")
//describe the program
System.out.println("This program computes the
monthly and total") System.out.println("p
ayments for a given loan amount, annual ")
System.out.println("interest rate, and loan
period.") System.out.println("Loan
amount in dollars and cents, e.g., 12345.50")
System.out.println("Annual interest rate in
percentage, e.g., 12.75")
System.out.println("Loan period in number of
years, e.g., 15") System.out.println("\n"
) //skip two lines
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Step 4 Code (2/3)
//get input values inputStr
JOptionPane.showInputDialog(null,
"Loan Amount
(DollarsCents)") loanAmount
Double.parseDouble(inputStr) inputStr
JOptionPane.showInputDialog(null,
"Annual Interest
Rate (e.g., 9.5)") annualInterestRate
Double.parseDouble(inputStr) inputStr
JOptionPane.showInputDialog(null,
"Loan Period - of
years") loanPeriod
Integer.parseInt(inputStr) //compute
the monthly and total payments
monthlyInterestRate annualInterestRate /
MONTHS_IN_YEAR / 100 numberOfPayments
loanPeriod MONTHS_IN_YEAR
monthlyPayment (loanAmount monthlyInterestRate
) / (1 -
Math.pow(1/(1 monthlyInterestRate),

numberOfPayments ) ) totalPayment
monthlyPayment numberOfPayments
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Step 4 Code (3/3)
//display the result
System.out.println("Loan Amount "
loanAmount) System.out.println("Annual
Interest Rate " annualInterestRate "")
System.out.println("Loan Period (years) "
loanPeriod) System.out.println("\n")
//skip two lines System.out.println("Month
ly payment is "
df.format(monthlyPayment))
System.out.println(" TOTAL payment is
"
df.format(totalPayment))
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End of Recitation 1