I/O in AP Java

Enjoyable, Meaningful, Non-Distracting I/O in AP Java

Ken Lambert, Washington and Lee UniversityMartin Osborne, Western Washington University

Copyright 2002

Free Supplemental Materials

www.cs.wwu.edu/martin Slides for this talk Software packages

– TerminalIO – TurtleGraphics– BreezySwing

Languages for Introductory Programming Fortran (60's) PL/1 (70's) Pascal and Modula (80's) C++ (90's) Java (2000 and beyond)

Why Java?

Pascal a teaching language C++ a developer's language Java a bit of both

– For teaching• Smaller, simpler syntax than C++

– For developer's• Safe, portable, vast supporting libraries

C++ I/O

Stream I/O– Simple, flexible– Supports both terminal and files– cin, cout for console– Stream objects for files– Suitable for introductory course

GUI's – Platform dependent– Complex – Not suitable for introductory course

Java I/O

Stream I/O – Moderately difficult– Several simple patterns cover basic situations– Somewhat suitable for introductory course

GUIs– Platform independent– Complex

• but several complex patterns cover basic situations

– Doable but not really suitable for introductory course

AP I/O Requirements

Terminal output with System.out Package supported stream input

– Basic read functions for intrinsic data types

Advantage of AP Approach Leaves more time for everything else Including some I/O that is

– Enjoyable– Meaningful– Non-distracting

Most Basic Program Structure

import …;

public class <ProgramName> {

public static void main(String [] args) {

… statements…

}

}

Console Applications

Temperature Conversion

User InterfaceEnter degrees Fahrenheit: 212

The equivalent in Celsius is 100.0

Implementation

import TerminalIO.KeyboardReader;

public class Convert {

public static void main(String [] args) {

double fahrenheit;

double celsius;

KeyboardReader reader = new KeyboardReader();

fahrenheit = reader.readDouble("Enter degrees Fahrenheit: ");

celsius = (fahrenheit - 32.0) * 5.0 / 9.0;

System.out.println("The equivalent in Celsius is " + celsius);

}

}

Menu Driven Conversion1) Convert from Fahrenheit to Celsius

2) Convert from Celsius to Fahrenheit

3) Quit

Enter your option: 1

Enter degrees Fahrenheit: 212

Degrees Celsius = 100.0

1) Convert from Fahrenheit to Celsius

2) Convert from Celsius to Fahrenheit

3) Quit

Enter your option: 2

Etc…

Implementation (1 of 2)

import TerminalIO.*;

public class ConvertWithMenu {

public static void main (String [] args) {

KeyboardReader reader = new KeyboardReader();

double fahrenheit, celsius;

String menu; //The multiline menu

int menuOption; //The user's menu selection

menu = "\n1) Convert from Fahrenheit to Celsius"

+ "\n2) Convert from Celsius to Fahrenheit"

+ "\n3) Quit"

+ "\nEnter your option: ";

Implementation (2 of 2)

do { menuOption = reader.readInt(menu); System.out.println (""); if (menuOption == 1){ fahrenheit = reader.readDouble("Enter degrees Fahrenheit: "); celsius = (fahrenheit - 32.0) * 5.0 / 9.0; System.out.println ("Degrees Celsius = " + celsius); }else if (menuOption == 2){ celsius = reader.readDouble("Enter degrees Celsius: "); fahrenheit = celsius * 9.0 / 5.0 + 32.0; System.out.println ("Degrees Fahrenheit = " + fahrenheit); }else if (menuOption != 3){ System.out.println ("Invalid option"); } } while (menuOption != 3); }}

Formatted Output

The number with precision 0: 1

The number with precision 1: 1.2

The number with precision 2: 1.23

The number with precision 3: 1.235

The number with precision 4: 1.2346

The number with precision 5: 1.23456

The number with precision 6: 1.234560

The number with precision 7: 1.2345600

The number with precision 8:1.23456000

The number with precision 9:**********

Implementation

import BreezySwing.Format;public class TerminalFormatDemo { public static void main (String [] args) { double number = 1.23456; for (int i = 0; i <= 9; i++){ String str = "The number with precision " + i + ":" + Format.justify ('r', number, 10, i); System.out.println (str); } }}

Temperature Conversion Revisited

User InterfaceEnter degrees Fahrenheit: 212

The equivalent in Celsius is 100.0

Native Implementation (1 of 2)

import java.io.*;

public class Convert{

public static void main (String[] args){

…

try{

InputStreamReader reader = new InputStreamReader(System.in);

BufferedReader buffer = new BufferedReader(reader);

… = Double.parseDouble(buffer.readLine());

… = Integer.parseInt(buffer.readLine());

…

}catch(Exception e){

System.err.println("Input error -- " + e.toString());

}

}

}

Native Implementation (2 of 2)

import java.io.*;

public class Convert{

public static void main (String[] args){

double fahrenheit;

double celsius;

try{

InputStreamReader reader = new InputStreamReader(System.in);

BufferedReader buffer = new BufferedReader(reader);

System.out.print("Enter degrees Fahrenheit: ");

fahrenheit = Double.parseDouble(buffer.readLine());

celsius = (fahrenheit - 32.0) * 5.0 / 9.0;

System.out.println("The equivalent in Celsius is " + celsius);

}catch(Exception e){

System.err.println("Input error -- " + e.toString());

}

}

}

Factoring Out the Complexitywith a static method (1 of 2)

import java.io.*;

public class Convert2{

public static void main (String[] args){

double fahrenheit;

double celsius;

fahrenheit = readDouble("Engter degrees Fahrehheit: ");

celsius = (fahrenheit - 32.0) * 5.0 / 9.0;

System.out.println("The equivalent in Celsius is " + celsius);

}

Factoring Out the Complexity with a static method (2 of 2)

public static double readDouble(String prompt){ double theNumber; try{ InputStreamReader reader = new InputStreamReader(System.in); BufferedReader buffer = new BufferedReader(reader); System.out.print(prompt); theNumber = Double.parseDouble(buffer.readLine()); return theNumber; }catch(Exception e){ System.err.println("Input error -- " + e.toString()); return 0; } }}

Factoring Out the Complexity with a supporting class (1 of 2)

public class Convert3 {

public static void main(String [] args) {

double fahrenheit;

double celsius;

KeyboardReader reader = new KeyboardReader();

fahrenheit = reader.readDouble("Enter degrees Fahrenheit: ");

celsius = (fahrenheit - 32.0) * 5.0 / 9.0;

System.out.println("The equivalent in Celsius is " + celsius);

}

}

Factoring Out the Complexity with a supporting class (2 of 2)import java.io.*;public class KeyboardReader{ public double readDouble(String prompt){ double theNumber; try{ InputStreamReader reader = new InputStreamReader(System.in); BufferedReader buffer = new BufferedReader(reader); System.out.print(prompt); theNumber = Double.parseDouble(buffer.readLine()); return theNumber; }catch(Exception e){ System.err.println("Input error -- " + e.toString()); return 0; } }}

Illustrating Concepts with Turtle Graphics

Draw a SquareInstantiating and sending messages to an object

Implementationimport TurtleGraphics.StandardPen;public class DrawSquare { public static void main (String [] args) {

// Instantiate a pen object StandardPen pen = new StandardPen(); // Lift the pen, move it to the square's top left corner, // and lower it again pen.up(); pen.move(25); pen.turn(90); pen.move(25); pen.down(); // Draw the square pen.turn(90); pen.move(50); pen.turn(90); pen.move(50); pen.turn(90); pen.move(50); pen.turn(90); pen.move(50); }}

Draw a 100-gonUsing for-statements

import TurtleGraphics.StandardPen;public class Draw100gon { public static void main (String [] args) { int i; StandardPen pen = new StandardPen(); // Lift, move to top of circle, lower pen.up(); pen.move(25); pen.turn(90); pen.move(0.8); pen.down(); // Draw the 100gon for (i = 1; i <= 100; i++){ pen.turn(3.6); pen.move(1.6); } }}

Implementation

Smiley FaceUser defined classes

Outline of Classpublic class SmilingFace {

public SmilingFace(){...}

public SmilingFace(double x, double y){...}

public void draw(){

public void erase(){

public void move(double x, double y){...}

private void drawCircle(double x, double y, double r){...}

private void drawLine(double x1, double y1,

double x2, double y2){...}

private StandardPen pen;

private double xPosition, yPosition;

}

Using the Classimport TurtleGraphics.*;import TerminalIO.*;public class TestSmilingFace { public static void main (String[] args){ KeyboardReader reader = new KeyboardReader(); double x, y, radius;

x = reader.readDouble("Initial x position: "); y = reader.readDouble("Initial y position: "); SmilingFace face = new SmilingFace(x, y); face.draw (); while (true){ x = reader.readDouble("New x position: "); y = reader.readDouble("New y position: "); face.erase(); face.move(x, y); face.draw(); } }}

Implementation of Class (1 of 4)

import TurtleGraphics.*;

import java.awt.Color;

public class SmilingFace {

private StandardPen pen;

private double xPosition, yPosition;

public SmilingFace(){

xPosition = 0;

yPosition = 0;

pen = new StandardPen();

pen.setColor(Color.red);

}

public SmilingFace(double x, double y){

this();

xPosition = x;

yPosition = y;

}

Implementation of Class (2 of 4)

public void erase(){

pen.setColor(Color.white);

draw();

pen.setColor(Color.red);

}

public void move(double x, double y){

xPosition = x;

yPosition = y;

}

Implementation of Class (3 of 4)

public void draw(){

double radius = 50.0;

// Draw the outline of the face

drawCircle(xPosition, yPosition, radius);

// Draw the left and right eye.

drawCircle(xPosition - radius / 2.5, yPosition + radius / 3, radius / 4);

drawCircle(xPosition + radius / 2.5, yPosition + radius / 3, radius / 4);

// Draw the horizontal part of the mouth

drawLine(xPosition - radius / 3, yPosition - radius / 2,

xPosition + radius / 3, yPosition - radius / 2);

// Draw the left and right smile line

drawLine(xPosition - radius / 3 , yPosition - radius / 2,

xPosition - radius / 3 - 5, yPosition - radius / 2 + 5);

drawLine(xPosition + radius / 3 , yPosition - radius / 2,

xPosition + radius / 3 + 5, yPosition - radius / 2 + 5);

}

Implementation of Class (4 of 4)

private void drawCircle(double x, double y, double r){ double side = 2.0 * Math.PI * r / 120.0; pen.up(); pen.move(x + r, y - side / 2.0); pen.setDirection(90); pen.down(); for (int i = 0; i < 120; i++){ pen.move(side); pen.turn(3); } }

private void drawLine(double x1, double y1, double x2, double y2){ pen.up(); pen.move(x1, y1); pen.down(); pen.move(x2, y2); }}

FractalsRecursion

Implementation (1 of 2)

import java.awt.Color;

import TurtleGraphics.*;

public class Recursion {

public static void main (String [] args) {

Pen pen = new StandardPen();

pen.setWidth(1);

for (int i = 1; i <= 6; i++){

pen.up();

pen.move(-100, 245 - 70 * i);

pen.down();

pen.setDirection(0);

drawFractal(i, pen, 200);

}

}

Implementation (2 of 2)

private static void drawFractal(int depth, Pen pen, double length){

if (depth <= 1)

pen.move(length);

else{

drawFractal(depth - 1, pen, length / 3);

pen.turn(60);

drawFractal(depth - 1, pen, length / 3);

pen.turn(-120);

drawFractal(depth - 1, pen, length / 3);

pen.turn(60);

drawFractal(depth - 1, pen, length / 3);

}

}

}

Drawing in Applets

Implementationimport java.applet.Applet;import java.awt.Graphics;import java.awt.Graphics2D;import java.awt.Rectangle;import java.awt.geom.Ellipse2D;import java.awt.geom.Line2D;import java.awt.geom.Point2D;

public class Shapes extends Applet{ public void paint(Graphics g){ Graphics2D g2 = (Graphics2D)g; Rectangle rectangle = new Rectangle(50, 50, 100, 50); Ellipse2D.Double ellipse = new Ellipse2D.Double(50, 50, 100, 50); Point2D.Double point1 = new Point2D.Double(50, 50); Point2D.Double point2 = new Point2D.Double(150, 100); Line2D.Double line = new Line2D.Double(point1, point2); g2.draw(rectangle); g2.draw(ellipse); g2.draw(line); }}

GUIs

A Simple GUI

Breezy Implementation (1 of 4)

import javax.swing.*;

import BreezySwing.*;

public class ConvertWithGUI extends GBFrame{

private JLabel fahrenheitLabel;

private JLabel celsiusLabel;

private DoubleField fahrenheitField;

private DoubleField celsiusField;

private JButton fahrenheitButton;

private JButton celsiusButton;

Breezy Implementation (2 of 4)

public ConvertWithGUI(){

fahrenheitLabel = addLabel ("Fahrenheit" ,1,1,1,1);

celsiusLabel = addLabel ("Celsius" ,1,2,1,1);

fahrenheitField = addDoubleField (32.0 ,2,1,1,1);

celsiusField = addDoubleField (0.0 ,2,2,1,1);

fahrenheitButton = addButton (">>>>>>" ,3,1,1,1);

celsiusButton = addButton ("<<<<<<" ,3,2,1,1);

}

Breezy Implementation (3 of 4)

public void buttonClicked (JButton buttonObj){ double fahrenheit, celsius; if (buttonObj == fahrenheitButton){ fahrenheit = fahrenheitField.getNumber(); celsius = (fahrenheit - 32.0) * 5.0 / 9.0; celsiusField.setNumber (celsius); }else{ celsius = celsiusField.getNumber(); fahrenheit = celsius * 9.0 / 5.0 + 32.0; fahrenheitField.setNumber (fahrenheit); } }

Breezy Implementation (4 of 4)

public static void main (String[] args){

ConvertWithGUI theGUI = new ConvertWithGUI();

theGUI.setSize (250, 100);

theGUI.setVisible (true);

}

Native Implementation (1 of 6)

import java.awt.*;

import javax.swing.*;

import java.awt.event.*;

public class ConversionWithSwing extends JFrame{

private JLabel fahrenheitLabel;

private JTextField fahrenheitField;

private JLabel celsiusLabel;

private JTextField celsiusField;

private JButton fahrenheitButton;

private JButton celsiusButton;

Native Implementation (2 of 6)

public ConversionWithSwing(){

fahrenheitLabel = new JLabel ("Fahrenheit");

celsiusLabel = new JLabel ("Celsius");

fahrenheitField = new JTextField ("212", 6); // 6 columns wide

celsiusField = new JTextField ("100", 6); // 6 columns wide

fahrenheitButton = new JButton (">>>>>>");

celsiusButton = new JButton ("<<<<<<");

Native Implementation (3 of 6)

Container contentPane = getContentPane();

contentPane.setLayout (new FlowLayout());

contentPane.add (fahrenheitLabel);

contentPane.add (celsiusLabel);

contentPane.add (fahrenheitField);

contentPane.add (celsiusField);

contentPane.add (fahrenheitButton);

contentPane.add (celsiusButton);

fahrenheitButton.addActionListener(new MyActionListener());

celsiusButton.addActionListener(new MyActionListener());

addWindowListener(new MyWindowAdapter());

}

Native Implementation (4 of 6)

public static void main (String[] args){

ConversionWithSwing theGUI = new ConversionWithSwing();

theGUI.setSize (200, 125);

theGUI.setVisible (true);

}

Native Implementation (5 of 6) private class MyActionListener implements ActionListener{ public void actionPerformed (ActionEvent event){ double fahrenheit, celsius; String str; Object source = event.getSource(); if (source == fahrenheitButton){ str = fahrenheitField.getText().trim(); fahrenheit = Double.parseDouble(str); celsius = (fahrenheit - 32) * 5 / 9; celsiusField.setText ("" + celsius); }else{ str = celsiusField.getText().trim(); celsius = Double.parseDouble(str); fahrenheit = celsius * 9 / 5 + 32; fahrenheitField.setText ("" + fahrenheit); } } }

Native Implementation (6 of 6)

private class MyWindowAdapter extends WindowAdapter{

public void windowClosing (WindowEvent e){

System.exit(0);

}

}

}

Drawback of Flow Layout Fields move around when window

resized Solution – use a gridbag layout

– Unfortunately, considerably more complex

Summary

AP Java has minimal I/O requirements Take advantage of this to

– Have fun and– Add interest

While – providing useful skills and– Avoiding unnecessary complexity