Ihsan Ayyub Qazi (ihsan@cs.pitt.edu)

Introduction to Computer Programming

Recitation 3Ihsan Ayyub Qazi

Ihsan Ayyub Qazi (ihsan@cs.pitt.edu)

Agenda

Project Questions FTP Dialog Boxes Classes and Objects Scanner Class

Ihsan Ayyub Qazi (ihsan@cs.pitt.edu)

Project: Any Questions? Goal: Make a Tip Calculator Input:

Total bill Tip percentage Number of people splitting the bill

Output: Tip amount Total to pay Total per person

Requirements: JOptionPane class must be used for input and output Atleast two different data types must be used

Extra Credit: Use DecimalFormat class

Ihsan Ayyub Qazi (ihsan@cs.pitt.edu)

Dialog Boxes: JOptionPane Class

Java API has a class that allows you to create dialog boxes JOptionPane

import javax.swing.JOptionPane; JOptionPane.showMessageDialog(null,

"Hello"); JOptionPane.showInputDialog("Enter name");

returns a String How can we convert a String into a number?

Why not casting? Strings are not primitive data types?

Ihsan Ayyub Qazi (ihsan@cs.pitt.edu)

Converting Strings to numbers

byte age = Byte.parseByte(“7"); short year = Short.parseShort(“1007"); int bigNum = Integer.parseInt(“82456"); long bigNum2 =

Long.parseLong("6743210"); float price = Float.parseFloat("1.99"); double sum =

Double.parseDouble("72.345");

Ihsan Ayyub Qazi (ihsan@cs.pitt.edu)

Output?import javax.swing.JOptionPane; public class Test{ public static void main(String args []) {

String input; float value;int con;

input = JOptionPane.showInputDialog("Enter your GPA);value = Float.parseFloat(input);con = value; JOptionPane.showMessageDialog(null, “Your GPA is ”+con);

}}

Ihsan Ayyub Qazi (ihsan@cs.pitt.edu)

What is a class? An object? Consider a bicycle of a particular model from a

given company

Thousands of such bicycles may have been manufactured and sold

Each bicycle was built from the same set of blueprints and therefore contains the same components

In object-oriented terms, we say that your bicycle is an instance of the class (of objects) known as bicycles.

A class is the blueprint from which individual objects are created.

Ihsan Ayyub Qazi (ihsan@cs.pitt.edu)

Variables

What does a primitive type variable store? holds data items

What does class type variables store? holds references (or address of an object)

Ihsan Ayyub Qazi (ihsan@cs.pitt.edu)

Bicycle class: Output?public class Bicycle {

int speed = 0; int gear = 1;

void changeGear(int newValue) { gear = newValue;

}

void speedUp(int increment) { speed = speed + increment;

}

void applyBrakes(int decrement) { speed = speed - decrement; }

void printStates() { System.out.println(" speed:"+speed+" gear:"+gear);}}

public static void main(String args []) {

Bicycle bike = new Bicycle();

bike.speed = 34; bike.gear = 3; bike.changeGear(5); bike.speedUp(3); bike.printStates(); bike.applyBrakes(5); bike.printStates();

}

Attributes

Method

Creating an

instance of a class

Ihsan Ayyub Qazi (ihsan@cs.pitt.edu)

In-class problem

Create two objects of type Bicycle name them bike1 and bike2

The output of the program should be speed:10 gear:2 // bike 1 speed:7 gear:2 // bike 2 speed:30 gear:4 // bike 1 speed:32 gear:4 // bike 2 speed:5 gear:2 // bike 1 [bicycle goes down, tough

luck !]

speed:40 gear:5 // bike 2

Ihsan Ayyub Qazi (ihsan@cs.pitt.edu)

Quick Review: Scanner Class

Another method for getting user input! One can get input in different data formats import java.util.Scanner; Some Scanner Class methods

Method Name Returns Input As

nextByte byte

nextDouble double

nextFloat float

nextInt int

nextLine String

nextLong long

nextShort short

Ihsan Ayyub Qazi (ihsan@cs.pitt.edu)

public class Payroll{ public static void main(String[] args) { String name; // To hold a name int hours; // Hours worked double payRate; // Hourly pay rate double grossPay; // Gross pay // Create a Scanner object to read input. Scanner keyboard = new Scanner(System.in); // Get the user's name. System.out.print("What is your name? "); name = keyboard.nextLine(); // Get the number of hours worked this week. System.out.print("How many hours did you work this week? "); hours = keyboard.nextInt(); // Get the user's hourly pay rate. System.out.print("What is your hourly pay rate? "); payRate = keyboard.nextDouble(); // Calculate the gross pay. grossPay = hours * payRate; // Display the resulting information. System.out.println("Hello " + name); System.out.println("Your gross pay is $" + grossPay); }}

Ihsan Ayyub Qazi (ihsan@cs.pitt.edu)

THANKS !!