Pedro Fonseca

I guess I don't...?

Gotta be honest, I'm yet to properly wrap my head around everything regarding connections, I understand the very basic bare bones (if that much).

EDIT: How can I add a listener to that code so it allows me to test it?

Something like printing the sent message on the terminal window, but anything will do.

I'm currently doing some server-related exercises, but can't make my localhost accept connections.

I'm using a MacBook Pro running Snow Leopard, the apache is turned on, firewall was off (I did try to turn it on and tell it to enable incoming connections, but didn't work) and I have Growl installed (tried disabling it already).

Here's the code I'm using:
import java.io.*; import java.net.*; import javax.swing.*; import java.awt.*; import java.awt.event.*; public class SimpleChatClientA { JTextField outgoing; PrintWriter writer; Socket sock; public void go() { // make gui and register a listener with the send button // call the setUpNetworking() method JFrame frame = new JFrame("Ludicrously Simple Chat Client"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); JPanel mainPanel = new JPanel(); outgoing = new JTextField(20); JButton sendButton = new JButton("Send"); sendButton.addActionListener(new SendButtonListener()); mainPanel.add(outgoing); mainPanel.add(sendButton); frame.getContentPane().add(BorderLayout.CENTER, mainPanel); setUpNetworking(); frame.setSize(400,500); frame.setVisible(true); } private void setUpNetworking() { // make a Socket, then make a PrintWriter // assign the PrintWriter to writer instance variable try { sock = new Socket("127.0.0.1", 5000); writer = new PrintWriter(sock.getOutputStream()); System.out.println("networking established"); } catch (IOException ex) { ex.printStackTrace(); } } public class SendButtonListener implements ActionListener { public void actionPerformed(ActionEvent ev) { // get the text from the text field and // send it to the server using the writer (a PrintWriter) try { writer.println(outgoing.getText()); writer.flush(); } catch(Exception ex) { ex.printStackTrace(); } outgoing.setText(""); outgoing.requestFocus(); } } public static void main(String[] args) { new SimpleChatClientA().go(); } }
And here's the exception stack
java.net.ConnectException: Connection refused at java.net.PlainSocketImpl.socketConnect(Native Method) at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:351) at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:213) at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:200) at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:432) at java.net.Socket.connect(Socket.java:529) at java.net.Socket.connect(Socket.java:478) at java.net.Socket.<init>(Socket.java:375) at java.net.Socket.<init>(Socket.java:189) at SimpleChatClientA.setUpNetworking(SimpleChatClientA.java:33) at SimpleChatClientA.go(SimpleChatClientA.java:24) at SimpleChatClientA.main(SimpleChatClientA.java:57)
Searching around I found this command line to test the connection, but it gives me a connection refused too.
telnet localhost 5000

Whoa, thank you very much, it worked like a charm!

I didn't know/think that it meant declaring a new variable (and I did the same to the question variable).

Looking at it again, the book code doesn't declare them again, so it is most probably something I typed without properly realizing it and then proceeded to focus on the wrong part of the problem.

Anyway, again, I thank you very much for your help, Paul, I was already getting kinda desperate for not figuring what was wrong with the code.

Hello everyone, I'm studying Java with the Head First Java book and currently am at the I/O chapter, so one of the exercises is to make a Quiz Card class, builder and player.

However, I'm having issues with the builder as, for some reason, the program is not being able to read the content in the JTextAreas where you type your desired question and answer, whenever I try to do anything with the data, it throws a NullPointerException at runtime, even if the field is not blank and even after putting a setText() just before it.

If anyone could give me any insight of what is going wrong, I'd really appreciate it as I wasn't able to find any iffy code (I might be wrong) or a way to make it work, trying everything in my still limited knowledge to fix it, such as the aforementioned setText(), checking if the problem was the button, etc.

Here's the code as provided in the book (and from what I've learned so far, it was supposed to work):
import java.util.*; import java.awt.event.*; import javax.swing.*; import java.awt.*; import java.io.*; public class QuizCardBuilder { private JTextArea question; private JTextArea answer; private ArrayList<QuizCard> cardList; private JFrame frame; JScrollPane qScroller; public static void main (String[] args) { QuizCardBuilder builder = new QuizCardBuilder(); builder.go(); } public void go() { // build gui frame = new JFrame("Quiz Card Builder"); JPanel mainPanel = new JPanel(); Font bigFont = new Font("sanserif", Font.BOLD, 24); JTextArea question = new JTextArea(6,20); question.setLineWrap(true); question.setWrapStyleWord(true); question.setFont(bigFont); qScroller = new JScrollPane(question); qScroller.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS); qScroller.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER); JTextArea answer = new JTextArea(6,20); answer.setLineWrap(true); answer.setWrapStyleWord(true); answer.setFont(bigFont); JScrollPane aScroller = new JScrollPane(answer); aScroller.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS); aScroller.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER); JButton nextButton = new JButton("Next Card"); cardList = new ArrayList<QuizCard>(); JLabel qLabel = new JLabel("Question"); JLabel aLabel = new JLabel("Answer"); mainPanel.add(qLabel); mainPanel.add(qScroller); mainPanel.add(aLabel); mainPanel.add(aScroller); mainPanel.add(nextButton); nextButton.addActionListener(new NextCardListener()); JMenuBar menuBar = new JMenuBar(); JMenu fileMenu = new JMenu("File"); JMenuItem newMenuItem = new JMenuItem("New"); JMenuItem saveMenuItem = new JMenuItem("Save"); newMenuItem.addActionListener(new NewMenuListener()); saveMenuItem.addActionListener(new SaveMenuListener()); fileMenu.add(newMenuItem); fileMenu.add(saveMenuItem); menuBar.add(fileMenu); frame.setJMenuBar(menuBar); frame.getContentPane().add(BorderLayout.CENTER, mainPanel); frame.setSize(500,600); frame.setVisible(true); } public class NextCardListener implements ActionListener { public void actionPerformed(ActionEvent ev) { QuizCard card = new QuizCard(question.getText(),answer.getText()); cardList.add(card); clearCard(); } } public class SaveMenuListener implements ActionListener { public void actionPerformed(ActionEvent ev) { QuizCard card = new QuizCard(question.getText(), answer.getText()); cardList.add(card); JFileChooser fileSave = new JFileChooser(); fileSave.showSaveDialog(frame); saveFile(fileSave.getSelectedFile()); } } public class NewMenuListener implements ActionListener { public void actionPerformed(ActionEvent ev) { cardList.clear(); clearCard(); } } private void clearCard() { question.setText(""); answer.setText(""); question.requestFocus(); } private void saveFile(File file) { try { BufferedWriter writer = new BufferedWriter(new FileWriter(file)); for(QuizCard card:cardList) { writer.write(card.getQuestion() + "/"); writer.write(card.getAnswer() + "\n"); } writer.close(); } catch(IOException ex) { System.out.println("Couldn't write the cardList out"); ex.printStackTrace(); } } }

It also uses a separate QuizCard class, which anyone using the book should write on their own and mine's as such:
public class QuizCard { private String theQuestion = "All questions"; private String theAnswer = "42"; public QuizCard(String q, String a) { theQuestion = q; theAnswer = a; } public String getQuestion() { return theQuestion; } public String getAnswer() { return theAnswer; } }

I've considered the possibility of the problem being with my class, however testing everything by removing all instances where the separate class was called still gave me the exception, so it doesn't seem to be the problem (again, might be wrong).

Thanks in advance for any insights.

Good catch, thanks for the replies.

Indeed the problem was another Track.class in the same folder as the MiniMiniMusicApp, I have to be more cautious about this sort of thing in the future.

Ok, at first I typed everything just as in the book and...it didn't work, giving me a message that the Track symbol wasn't found.
import javax.sound.midi.*; public class MiniMiniMusicApp { public static void main(String [] args) { MiniMiniMusicApp mini = new MiniMiniMusicApp(); mini.play(); } public void play() { try { Sequencer player = MidiSystem.getSequencer(); player.open(); Sequence seq = new Sequence(Sequence.PPQ, 4); Track track = seq.createTrack(); //Here's where things go bad ShortMessage a = new ShortMessage(); a.setMessage(144, 1, 44, 100); MidiEvent noteOn = new MidiEvent(a, 1); track.add(noteOn); ShortMessage b = new ShortMessage(); b.setMessage(128, 1, 44, 100); MidiEvent noteOff = new MidiEvent(b, 16); track.add(noteOff); player.setSequence(seq); player.start(); Thread.sleep(2000); player.close(); System.exit(0); } catch (Exception ex) { ex.printStackTrace(); } } }

But much to my surprise, giving the full address of the Track object suddenly made everything work just fine!

[...] try { Sequencer player = MidiSystem.getSequencer(); player.open(); Sequence seq = new Sequence(Sequence.PPQ, 4); javax.sound.midi.Track track = seq.createTrack(); //Suddenly it works...why?? [...]

So I'm left wondering why in hell it didn't work previously, why didn't the import line work as intended? Is there any explanation at all?

Ow, duh!

I feel incredibly stupid to let such a simple mistake slip by, but thanks for the help it works like a clockwork now!

And thanks for the tip, it looks like it's indeed time to get an IDE.

Hello everyone, I just recently started studying Java on my own using the book Head First Java and everything was going rather smoothly until the sixth chapter with the battleship-ish game, where I'm getting an error I have no idea how to fix since from what I know so far, the code's supposed to work.

I did check the web for the error and found some answers, however, most of them did not apply here (at least I don't think they do) since I'm declaring a method and the ones that were somewhat similar didn't work at all (for example, there was one that mentioned that the code given in the HFJ website worked once a line was fixed, but here it didn't work either.

For those familiar with the book, both the DotCom and GameHelper classes are on the same folder as the DotComBust and I typed them myself (they both compiled just fine).

And not sure if it makes any difference (shouldn't), but I'm doing all this on a mac, using the text edit to type all the code (but I have converted it to plain text instead of the default rich text).

Well, without further ado, here's the code:
import java.util.*; public class DotComBust { private GameHelper helper = new GameHelper(); private ArrayList<DotCom> dotComList = new ArrayList<DotCom>(); private int numOfGuesses = 0; private void setUpGame(); DotCom one = new DotCom(); one.setName("Pets.com"); DotCom two = new DotCom(); two.setName("eToys.com"); DotCom three = new DotCom(); three.setName("Go2.com"); dotComsList.add(one); dotComsList.add(two); dotComsList.add(three); System.out.println("Your goal is to sink three dot coms:"); System.out.println("Pets.com, eToys.com and Go2.com"); System.out.println("Try to sink them all in the fewest number of guesses"); for (DotCom dotComToSet : dotComsList) { ArrayList<String> newLocation = helper.placeDotCom(3); dotComToSet.setLocationCells(newLocation); } } private void startPlaying(); while(!dotComsList.isEmpty()) { String userGuess = helper.getUserInput("Enter a guess: "); checkUserGuess(userGuess); } finishGame(); } private void checkUserGuess(String userGuess) { numOfGuesses++; String result = "miss"; for (DotCom dotComToTest : dotComsList) { result = dotComToTest.checkYourself(userGuess); if (result.equals("hit") { break; } if (result.equals("kill") { dotComsList.remove(dotComToTest); break; } } System.out.println(result); } private void finishGame() { System.out.println("All Dot Coms are dead! Your stock is now worthless!"); if (numOfGuesses <= 18) { System.out.println("It only took you " + numOfGuesses + " guesses."); System.out.println("You got out before you options sank."); } else { System.out.println("Took you long enough. "+ numOfGuesses +" guesses."); System.out.println("Fish are dancing with your options!"); } } public static void main (String[] args) { DotComBurst game = new DotComBurst(); game.setUpGame(); game.startPlaying(); } }

And here's the error list:
DotComBust.java:10: <identifier> expected one.setName("Pets.com"); ^ DotComBust.java:10: illegal start of type one.setName("Pets.com"); ^ DotComBust.java:12: <identifier> expected two.setName("eToys.com"); ^ DotComBust.java:12: illegal start of type two.setName("eToys.com"); ^ DotComBust.java:14: <identifier> expected three.setName("Go2.com"); ^ DotComBust.java:14: illegal start of type three.setName("Go2.com"); ^ DotComBust.java:15: <identifier> expected dotComsList.add(one); ^ DotComBust.java:15: <identifier> expected dotComsList.add(one); ^ DotComBust.java:16: <identifier> expected dotComsList.add(two); ^ DotComBust.java:16: <identifier> expected dotComsList.add(two); ^ DotComBust.java:17: <identifier> expected dotComsList.add(three); ^ DotComBust.java:17: <identifier> expected dotComsList.add(three); ^ DotComBust.java:19: <identifier> expected System.out.println("Your goal is to sink three dot coms:"); ^ DotComBust.java:19: illegal start of type System.out.println("Your goal is to sink three dot coms:"); ^ DotComBust.java:20: <identifier> expected System.out.println("Pets.com, eToys.com and Go2.com"); ^ DotComBust.java:20: illegal start of type System.out.println("Pets.com, eToys.com and Go2.com"); ^ DotComBust.java:21: <identifier> expected System.out.println("Try to sink them all in the fewest number of guesses"); ^ DotComBust.java:21: illegal start of type System.out.println("Try to sink them all in the fewest number of guesses"); ^ DotComBust.java:23: illegal start of type for (DotCom dotComToSet : dotComsList) { ^ DotComBust.java:23: ')' expected for (DotCom dotComToSet : dotComsList) { ^ DotComBust.java:23: <identifier> expected for (DotCom dotComToSet : dotComsList) { ^ DotComBust.java:28: class, interface, or enum expected private void startPlaying(); ^ DotComBust.java:29: class, interface, or enum expected while(!dotComsList.isEmpty()) { ^ DotComBust.java:31: class, interface, or enum expected checkUserGuess(userGuess); ^ DotComBust.java:32: class, interface, or enum expected } ^ DotComBust.java:34: class, interface, or enum expected } ^ DotComBust.java:38: class, interface, or enum expected String result = "miss"; ^ DotComBust.java:40: class, interface, or enum expected for (DotCom dotComToTest : dotComsList) { ^ DotComBust.java:42: class, interface, or enum expected if (result.equals("hit") { ^ DotComBust.java:44: class, interface, or enum expected } ^ DotComBust.java:47: class, interface, or enum expected break; ^ DotComBust.java:48: class, interface, or enum expected } ^ DotComBust.java:51: class, interface, or enum expected } ^ DotComBust.java:55: class, interface, or enum expected if (numOfGuesses <= 18) { ^ DotComBust.java:57: class, interface, or enum expected System.out.println("You got out before you options sank."); ^ DotComBust.java:58: class, interface, or enum expected } else { ^ DotComBust.java:60: class, interface, or enum expected System.out.println("Fish are dancing with your options!"); ^ DotComBust.java:61: class, interface, or enum expected } ^ DotComBust.java:64: class, interface, or enum expected public static void main (String[] args) { ^ DotComBust.java:66: class, interface, or enum expected game.setUpGame(); ^ DotComBust.java:67: class, interface, or enum expected game.startPlaying(); ^ DotComBust.java:68: class, interface, or enum expected } ^

The setName method refers to the DotCom class that is in another file at the same folder and is coded to take an n String. public void setName(String n)