Mehran Sahami Handout #40 CS 106A November 16, 2007 MusicShop Program (ComponentListener Example) File: MusicShop.java

Mehran Sahami Handout #40
CS 106A November 16, 2007
MusicShop Program (ComponentListener Example)
File: MusicShop.java
/*
* File: MusicShop.java
* --------------------
* This program handles the data management for a music
* shop, showing which albums are carried and how many copies
* are in stock. The program handles dynamic resizing of
* the program window.
*/
import acm.program.*;
import acm.util.*;
import java.awt.event.*;
import java.io.*;
import java.util.*;
import javax.swing.*;
public class MusicShop extends Program {
// Set up initial display with interactors and canvas
public void init() {
label = new JLabel("Album Name");
albumName = new JTextField(20);
add(label, SOUTH);
add(albumName, SOUTH);
canvas = new MusicShopDisplay();
add(canvas);
loadInventory();
addActionListeners();
albumName.addActionListener(this);
}
// Read file to get inventory information on all albums
private void loadInventory() {
try {
BufferedReader rd = new BufferedReader(
new FileReader("music-data.txt"));
while (true) {
String line = rd.readLine();
if (line == null) break;
Album album = parseLine(line);
inventory.put(album.getAlbumName(), album);
}
rd.close();
} catch(IOException ex) {
throw new ErrorException(ex);
}
}
– 2 –
// Parse a single line from inventory file and returns an Album
// object that contains the information from the line
private Album parseLine(String line) {
int albumNameStart = line.indexOf("[") + 1;
int albumNameEnd = line.indexOf("]");
String albumName = line.substring(albumNameStart, albumNameEnd);
int bandNameStart = line.indexOf("[", albumNameEnd + 1) + 1;
int bandNameEnd = line.indexOf("]", albumNameEnd + 1);
String bandName = line.substring(bandNameStart, bandNameEnd);
int numStockedStart = line.indexOf(" ", bandNameEnd + 1) + 1;
int numStocked = Integer.parseInt(
line.substring(numStockedStart));
return (new Album(albumName, bandName, numStocked));
}
// Update the display whenever the user enters a new album name
public void actionPerformed(ActionEvent e) {
if (e.getSource() == albumName) {
canvas.displayInventory(inventory.get(albumName.getText()));
}
}
/* Private instance variables */
private JLabel label;
private JTextField albumName;
private MusicShopDisplay canvas;
private HashMap<String,Album> inventory =
new HashMap<String,Album>();
}
File: MusicShopDisplay.java
/*
* File: MusicShopDisplay
* ----------------------
* This file handles the display of album inventory for the music shop.
* It provides dynamic redrawing of window contents when display is
* resized.
*/
import acm.graphics.*;
import java.awt.event.*;
public class MusicShopDisplay extends GCanvas
implements ComponentListener {
// Constructor
public MusicShopDisplay() {
addComponentListener(this);
lastAlbum = null;
}
– 3 –
// Display the album name, band name, and number in stock
// for a single album if it is in our inventory. Otherwise,
// just clear the display.
public void displayInventory(Album album) {
removeAll();
lastAlbum = album;
if (album != null) {
int numStocked = album.getNumStocked();
add(new GLabel("Album [" + album.getAlbumName() + "] by ["
+ album.getBandName() + "]"),
10, (getHeight() - BAR_HEIGHT) / 2 - SPACER);
// Display squares in dicating how many inventory
double nextX = SPACER;
for(int i = 0; i < numStocked; i++) {
double barLength = (getWidth() / (double)MAX_INVENTORY)
- SPACER;
GRect rect = new GRect(nextX,
(getHeight() - BAR_HEIGHT) / 2,
barLength, BAR_HEIGHT);
rect.setFilled(true);
add(rect);
nextX += barLength + SPACER;
}
GLabel label = new GLabel(numStocked + " in stock");
add(label, 10, (getHeight() + BAR_HEIGHT) / 2 +
SPACER + label.getAscent());
}
}
// Whenever we need to update the display, continue to
// display the last album shown
public void update() {
displayInventory(lastAlbum);
}
public void componentHidden(ComponentEvent e) { }
public void componentMoved(ComponentEvent e) { }
public void componentResized(ComponentEvent e) { update(); }
public void componentShown(ComponentEvent e) { }
/* constants */
private static final double BAR_HEIGHT = 20;
private static final double SPACER = 10;
private static final int MAX_INVENTORY = 20;
/* private instance variables */
private Album lastAlbum;
}
– 4 –
File: Album.java
/*
* File: Album.java
* ----------------
* Keeps track of all the information for one album
* in the music shop, including its name, the number
* in stock, and the band that its by.
*/
public class Album {
// Constructor
public Album(String album, String band, int stock) {
albumName = album;
bandName = band;
numStocked = stock;
}
public String getAlbumName() {
return albumName;
}
public String getBandName() {
return bandName;
}
public int getNumStocked() {
return numStocked;
}
// Returns a string representation of an album, listing
// the album name, the band name, and the number in stock
public String toString() {
return ("\"" + albumName +
"\" by " + bandName +
": " + numStocked + " in stock");
}
/* private instance variables */
private String albumName;
private String bandName;
private int numStocked;
}
File: music-data.txt
[Snakes and Arrows] [Rush] 10
[Synchronicity] [The Police] 12
[Piece of Mind] [Iron Maiden] 2
[Plans] [Death Cab For Cutie] 10
[So] [Peter Gabriel] 20