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Thread: Can't get JLabel to change text while program is running.

  1. #1
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    Default Can't get JLabel to change text while program is running.

    I'm writing a program that lists a word taken randomly from an array of words and has a text field next to it. When the user types something in the text field and presses enter, it should perform an update that changes the word among some other tasks. However, when I run it, I can see that an action is registered as having been performed because I put in a println, but the JLable won't change its text.

    Here's the code:
    package com.jollex.TypingTest;
     
    import javax.swing.*;
    import java.util.Random;
    import java.awt.event.*;
    import java.io.*;
     
    public class Screen {
    	JFrame frame;
    	JPanel contentPane;
    	static JLabel word;
    	static JTextField ans;
    	static int num = 270;
    	static int[] numbers = new int[271];
    	static int wordsCorrect = 0;
    	static int wordsTotal = 0;
    	static boolean timerOn = false;
    	boolean gameDone = false;
    	static String[] words = new String[269];
     
    	public Screen() {
    		//Create and set up the frame
    		frame = new JFrame("Typing Test");
    		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
     
    		//Create a content pane
    		contentPane = new JPanel();
     
    		//Create and add label
    		word = new JLabel(newWord());
    		contentPane.add(word);
     
    		//Create and add text field
    		ans = new JTextField(20);
    		contentPane.add(ans);
     
    		//Creates action listener for text field and adds it
    		ActionListener enter = new ActionListener() {
    			@Override
    			public void actionPerformed(ActionEvent e) {
    				if (timerOn == true) update();
    				//Test to see if action listener works (remove later)
    				System.out.println("Action performed.");
    			}
    		};
    		ans.addActionListener(enter);
     
     
    		//Add content pane to frame
    		frame.setContentPane(contentPane);
     
    		//Size and then display the frame
    		frame.pack();
    		frame.setVisible(true);
     
    		//Start timer
    		timerOn = true;
    		timer.start();
    	}
     
    	//Creates a 60 second timer
    	ActionListener updater = new ActionListener() {
    		int count=0;
    		public void actionPerformed(ActionEvent time) {
    			if (count >= 60000) {
    				timerOn = false;
    				timer.stop();
    				gameDone = true;
    			}
    			count++;
    		}
    	};
    	Timer timer = new Timer(0, updater);
     
    	/**
    	 *Updates the display:
    	 *Checks the answer
    	 *Sets the label to a new word
    	 *Selects all text in the text field.
    	 */
    	public static void update() {
    		checkAns();
    		word.setText(newWord());
    		ans.selectAll();
    	}
     
    	//Checks if the answer is correct and adds points accordingly.
    	private static void checkAns() {
    		String word = getCurrentWord();
    		String word2 = null;
    		word2 = getAns();
    		if (word2.equals(word)) {
    			wordsCorrect += 1;
    			wordsTotal += 1;
    		} else {
    			wordsTotal += 1;
    		}
    	}
     
    	//Returns a new word from the words array.
    	public static String newWord() {
    		return words[randomInt()];
    	}
     
    	//Returns current word being displayed in the label.
    	public static String getCurrentWord() {
    		return words[num];
    	}
     
    	//Returns text from text field.
    	public static String getAns() {
    		String userAns = null;
    		userAns = ans.getText();
    		return userAns;
    	}
     
    	//Keeps an array of numbers from 0-269. Returns a random number and removes that number after it's been used.
    	public static int randomInt() {
    		for (int i = 0; i < 271; i++) {
    			numbers[i] = i;
    		}
    		Random generator = new Random();
    		while (numbers[num] == 270) {
    			num = generator.nextInt(270);
    		}
    		numbers[num] = 270;
    		return num;
    	}
     
    	//Loads words from words.txt to a string array called words.
    	private static void loadWords() {
    		File wordFile = new File("words.txt");
    		FileReader in;
    		BufferedReader readFile;
    		String nextWord;
     
    		try {
    			in = new FileReader(wordFile);
    			readFile = new BufferedReader(in);
    			int i = 0;
    			while ((nextWord = readFile.readLine()) != null && i < words.length) {
    				words[i] = nextWord;
    				i++;
    			}
    			readFile.close();
    			in.close();
    		} catch (FileNotFoundException e) {
    			System.out.println("File does not exist or could not be found.");
    			System.err.println("FileNotFoundException: " + e.getMessage());
    		} catch (IOException e) {
    			System.out.println("Problem reading file.");
    			System.err.println("IOException: " + e.getMessage());
    		}
    	}
     
    	//Creates and shows the GUI
    	public static void runGUI() {
    		JFrame.setDefaultLookAndFeelDecorated(true);
     
    		@SuppressWarnings("unused")
    		Screen screen = new Screen();
    	}
     
    	public static void main(String[] args) {
    		loadWords();
    		javax.swing.SwingUtilities.invokeLater(new Runnable() {
    			public void run() {
    				runGUI();
    			}
    		});
    	}
    }


  2. #2
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    Default Re: Can't get JLabel to change text while program is running.

    You need to add lots more println statements to see what the code is doing. Print out the values of variables as they are used and changed.
    If you don't understand my answer, don't ignore it, ask a question.

  3. #3
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    Default Re: Can't get JLabel to change text while program is running.

    Quote Originally Posted by Norm View Post
    You need to add lots more println statements to see what the code is doing. Print out the values of variables as they are used and changed.
    Thanks for the advice, by placing some more println statements around, I figured out that it the problem isn't that the JLabel isn't updating, but I think the issue is with the randomInt() method because it is returning the same word every time, instead of giving a new random number. I'm not sure how to fix this.

  4. #4
    Super Moderator Norm's Avatar
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    Default Re: Can't get JLabel to change text while program is running.

    randomInt() method because it is returning the same word
    How does randomInt() generate the number it returns?
    If you don't understand my answer, don't ignore it, ask a question.

  5. #5
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    Default Re: Can't get JLabel to change text while program is running.

    It has it's own method that creates a random number generator using the java.util.Random class and then uses the nextInt() method to get the next random integer.

    Here's the method from my code:
    	public static int randomInt() {
    		for (int i = 0; i < 271; i++) numbers[i] = i;
    		Random generator = new Random();
    		while (numbers[num] == 270) num = generator.nextInt(270);
    		numbers[num] = 270;
    		return num;
    	}

    EDIT:
    I did some reading and found out I shouldn't be creating the Random generator inside my method, so I moved it outside the method, into just the class and now I have just the generator.nextInt(270) portion in the randomInt() method.

    Like so:
    	private Random generator = new Random();
    	public int randomInt() {
    		for (int i = 0; i < 271; i++) numbers[i] = i;
    		while (numbers[num] == 270) num = generator.nextInt(270);
    		numbers[num] = 270;
    		return num;
    	}

    However, the random generator is still returning the same integer every time I run randomInt() by causing an action event.

  6. #6
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    Default Re: Can't get JLabel to change text while program is running.

    Try debugging the method by adding some printlns to see what values the variables in the method have.
    The printout should show you what is happening.


    The code has some hard coded magic numbers (270 and 271) that should not be coded that way.
    The values should be defined as variables or obtained from other sources like the length of an array.
    If you don't understand my answer, don't ignore it, ask a question.

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    Default Re: Can't get JLabel to change text while program is running.

    I figured it out, the for loop in my randomInt() method was loading the numbers array with the integers from 0-270 every time I called the randomInt() method, so I moved it out into it's own method called loadRandom() which is only run once, before the GUI is loaded. Thank you for the help, adding the println statements in really helped me and I will keep that in mind the next time problems arise.

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