Ihsan Ayyub Qazi Introduction to Computer Programming Recitation 3 Ihsan Ayyub Qazi

Ihsan Ayyub Qazi Agenda  Project Questions  FTP  Dialog Boxes  Classes and Objects  Scanner Class

Ihsan Ayyub Qazi 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 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 Converting Strings to numbers  byte age = Byte.parseByte( “7 ");  short year = Short.parseShort( “ 1007");  int bigNum = Integer.parseInt( “ 82456");  long bigNum2 = Long.parseLong( " ");  float price = Float.parseFloat("1.99");  double sum = Double.parseDouble("72.345");

Ihsan Ayyub Qazi 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 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 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 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(); } Attribute s Method Creating an instance of a class

Ihsan Ayyub Qazi 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 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 NameReturns Input As nextBytebyte nextDoubledouble nextFloatfloat nextIntint nextLineString nextLonglong nextShortshort

Ihsan Ayyub Qazi 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 THANKS !!