Lecture 8

Review (Methods of Math class)

int abs( int num )

double sqrt( double num )

double pow( double num, double power )

Method parametersData type of the result

Please take a look more Math methods at

http://java.sun.com/j2se/1.4.2/docs/api/java/lang/Math.html#method_summary

Example

double area = 2.25;

double value2 = Math.sqrt( area );

System.out.println( “value2 is “ + value2);

value2 is 1.5

2.25

Example

double PI = 3.14;

double radius = 1.5;

double area = PI * Math.pow( radius, 2 );

System.out.println( “Area is “ + area);

pow method takes two variables(radius)2

More Methods of Math class

Please take a look more Math methods athttp://java.sun.com/j2se/1.4.2/docs/api/java/lang/Math.html#method_summary

Today’s topic

• Java application– Let’s write codes for calculator application

• Constant variable

• Talk about project 1

User

JavaApplication

Programmer(who we are)

JavaProgram

Write

Use

Create

User Interface

• There are three actors– Programmer: who writes codes for applications– Computer: who runs applications– User: who uses applications

• Programmers have to consider two interactions– Programmer Computer– Computer User

– So, programmers write codes for user interface• how users interacts with applications

For example

User

Programmer(who we are)

Application

For example

User

Programmer(who we are)

User interface

Application should direct users

Example (MyCalculator.java)

Please create a new folder, named Example

Please download “acm.jar” file into the folder athttp://www.cs.umb.edu/~chonho/teaching/2007/files/

In Dr.Java, add acm.jar file for extra classpathin preference window from [edit]

Create a new file, named MyCalculator.java

and save it into the folder

MyCalculator.java

Let’s start with class header and main method

public class MyCalculator{

public static void main(String[] argv){

}}

MyCalculator.java (1)/* * File name: MyCalculator.java * -------------------------- * This program runs as a Java application without using

the acm.program package. */

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

public class MyCalculator{

Comment

Single line: //Multiple lines: /* … */

Class name

It should be same as file name

MyCalculator.java (2)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);

Create classesJFrame classIOConsole class

Frame title

Methods of JFrame class

MyCalculator.java (3)

int num1, num2, total;

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

num1 = console.readInt( “Enter num1: “ ); num2 = console.readInt( “Enter num2: “ );

total = num1 + num2;

console.println("The total is " + total + ".");}

}

readInt( ) methodask users to enter an integer numberit receives 1 string parameter

println()same as System.out.println() but, print out message in consoleit receives 1 string parameter

Constant variable

• Constant variable is static, and its value does not change within entire programs.– You can deal with it as regular variable

• Declaration of constant variable– Regular variable

double average;– Constant

static final double PI = 3.14;

Exercise

• 1. Mile to Kilometer conversion

• 2. Fahrenheit to Celsius conversion

• 3. Circle circumference and area

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{ 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);

double mile, kilo;

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

kilo = 1.6 * mile; console.println( mile + “ mile is " + kilo + “ kilometer");

}}

Constant Variable

double mile, kilo;

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

kilo = 1.6 * mile; console.println( mile + “ mile is " + kilo + “ kilometer");

static final double MileToKilometer = 1.6;

double mile, kilo;

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

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

Add this line asan attribute in a class

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.

Exercise 3 (comment out previous one)

• Circle circumference and area

PI = 3.14

circumference = 2 * PI * radius

area = PI * (radius)2

Create a calculator application to compute the circumference and area of circle

- Ask an user to enter number for radius of circle

- Calculate the circumference and are

- Print out both results for the user.

radius

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++){ num1 = console.readInt( “Enter num1: “ );

num2 = console.readInt( “Enter num2: “ );total = num1 + num2;

console.println("The total is " + total + ".");

}