Lecture 9

Today’s topic

• Let’s continue to do exercise (Lecture 8)

• Character data type– Char

• String class– String

Exercise 1

• Mile to Kilometer conversion

1 Mile is 1.6 Kilometer

Create a calculator application to convert unit from Mile to Kilometer

- Ask an user to enter one number in mile

- Calculate the unit conversion

- Print out the result in Kilometer for the user.

public class MyCalculator{ static final double MileToKilometer = 1.6;

public static void main(String[] argv) {

JFrame frame = new JFrame(“My Calculator");

IOConsole console = new IOConsole();

frame.getContentPane().add(BorderLayout.CENTER, console);

frame.setSize(500, 300);

frame.setVisible(true);

console.println( "This program converts mile to kilometer.” ); double mile = console.readDouble( “Enter number in mile: “ );

double kilo = MileToKilometer * mile; console.println( mile + “ mile is " + kilo + “ kilometer");

}}

Exercise 2 (comment out previous one)

• Fahrenheit Tf to Celsius Tc conversion

Conversion formulaTc = (5 / 9) * (Tf – 32)

Create a calculator application to convert unit from degree Fahrenheit to Celsius

- Ask an user to enter number in Tf- Calculate the unit conversion- Print out the result in Tc for the user.

public class MyCalculator{

public static void main(String[] argv) {

JFrame frame = new JFrame(“My Calculator");

IOConsole console = new IOConsole();

frame.getContentPane().add(BorderLayout.CENTER, console);

frame.setSize(500, 300);

frame.setVisible(true);

console.println( "This program converts F degree to C degree.” ); double Tf = console.readDouble( “Enter degree in F: “ );

double Tc = (5.0/9.0) * (Tf – 32); console.println( Tf + “ F degree is " + Tc + “ C degree");

}}

Extra methods in IOConsole

setForeground( Color )where Color will be one of colors such as

Color.Red, Color.Blue, Color.Green, etc. (page 43)

setFont( Font )where Font will be Font object as follow(page 42)

Font font = new Font( family, style, size );family: “Serif”, “SansSerif”, “Monospaced”,

etcstyle: Font.PLAIN, Font.BOLD, Font.ITALICsize: integer

Extra methods in JFrame

setLocation( int x, int y )

move a window to (x, y) position of the screen

public class MyCalculator{

public static void main(String[] argv) {

JFrame frame = new JFrame(“My Calculator");

IOConsole console = new IOConsole();

Font font = new Font( “Serif”, Font.ITALIC, 20);

console.setFont( font );

console.setColor( Color.GREEN );

frame.getContentPane().add(BorderLayout.CENTER, console);

frame.setLocation(200,300);

frame.setSize(500, 300);

frame.setVisible(true);

Challenge

• If you want to do calculation twice or more without closing windows, then you can use loop to ask users for entering new numbers.

console.println( "This program adds two numbers.” );

for( int i=0; i<5; i++){ console.println( "This program converts F degree to C degree.” ); double Tf = console.readDouble( “Enter degree in F: “ );

double Tc = (5.0/9.0) * (Tf – 32); console.println( Tf + “ F degree is " + Tc + “ C degree");

}

Exercise 3 (comment out previous one)

• Circle circumference and areaPI = 3.14circumference = 2 * PI * radiusarea = PI * (radius)2

radius

• Let’s create a new class, named MyCircle– So, the file name should be MyCircle.java– MyCircle is an application to calculate the

circumference and area of the circle, whose radius is provided by users

Exercise 3 (start with this)

/* File name: MyCircle.java by Chonho Lee -------------------------- This program calculates the circumference and area of

circle */

import acm.io.*;import java.awt.*;import javax.swing.*;

public class MyCircle{

}

Comment

Import packages

Today’s topic

• Character data type– Char

• String class– String

Character

• Character is one of primitive data types of variable (such as integer and double)

• Character variable contains one character as its value– Alphabet: a, b, c,…,A, B, C,…– Digit: 0, 1, 2, …– Symbol: +, -, =, !, <, >, $, %, …

Declaration of Character Variable

We use keyword char

Similar to integer and double

char ch = ‘b’;

Data type Variable name Value

Singlequotation mark

Examples of char variable

char grade = ‘B’;char plus = ‘+’;char num5 = ‘5’;

System.out.println( “My grade is “ + grade );System.out.println( “My grade is “ + grade + plus);System.out.println( num5 + plus + num5 + “ is 10“ ); On the screen, you will see

My grade is BMy grade is B+5+5 is 10

Strings

• String is basically just a collection of characters.

• Thus, the string “O’Bryant” could be thought of as a sequence of 8-elements ('O', '’', ‘B', 'r', ‘y', ‘a‘, ‘n’, ‘t’).

Strings in java

• String is a class in Java• Strings are constant (values cannot be changed

once they are created)

• Set of characters “Chonho Lee" is a string.

• "A" is a string, 'A' is a character.Note:Characters are delimited by single quotes and Strings are delimited by double quotes.

Capital !

int val = 10; val 10

String name = new String(“Chonho”);

String name = “Chonho”;

Simplify!

Since String is a classCreate object! (declare object)

Declare variable

Declaration

String classname Chonho

Examples of String

String name = “Chonho”;String job = “Student at UMB”;String id = “4816828”;String email = “chonho@gmail.com”

System.out.println( name + “ information” ); System.out.println( “Who? “ + job + “, ID: “ + id );System.out.println( “Please email at “ + email );On the screen, you will see

Chonho informationWho? Student at UMB, ID: 4816828Please email at chonho@gmail.com

Today’s Exercise

• Name card creator– Let’s create a name card by name card

creator application– Write a class, named MyNameCard

• Ask an user to enter first name• Ask an user to enter last name• Ask an user to enter age• Print out the results

public class MyNameCard{

public static void main(String[] argv) {

JFrame frame = new JFrame(“My Calculator");

IOConsole console = new IOConsole();

frame.getContentPane().add(BorderLayout.CENTER, console);

frame.setSize(500, 300);

frame.setVisible(true);

console.println( "This program create a name card for users” ); String first = console.readLine( “Enter first name: “ ); String last = console.readLine( “Enter last name: “ ); String age = console.readLine( “Enter your age: “ ); console.println( “Hi, my name is “ + first + “ “ + last ); console.println( “I am “ + age + “ years old” );}

}