Prompt for value in swing thread
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  1. #1
    Join Date
    Dec 2010
    Posts
    0

    Question Prompt for value in swing thread

    Hi

    I need to control the gui from the application logic. So here is a simple example of what I need to do:

    It starts a main thread, prompts for a value using a swing gui, while the main thread is waiting. The main thread needs to resume when the button is clicked.

    I get an IllegalMonitorStateException when the gui thread tries to tell the main thread to resume because it is not the owner.

    Thanks in advance.

    Code:
    package example.gui;
    
    import java.awt.event.ActionEvent;
    import java.awt.event.ActionListener;
    import javax.swing.*;
    import java.util.concurrent.locks.Condition;
    import java.util.concurrent.locks.Lock;
    import java.util.concurrent.locks.ReentrantLock;
    
    public class TextInput implements Runnable {
        LockMechanism lm = new LockMechanism();
        String value = "";
        private final String prompt;
    
        /**
         * Get a value from a swing gui
         * 
         * @param args
         * @throws InterruptedException
         */
        public static void main(String[] args) throws InterruptedException {
            String v = TextInput.getInput("Enter a number");
            System.out.println("You entered " + v);
        }
    
        /**
         * Start a swing gui in a new thread to prompt from a value
         *
         * @param prompt
         * @return
         */
        public static String getInput(String prompt) {
            TextInput ti = new TextInput(prompt);
            try {
                Thread t = new Thread(ti, "gui");
                try {
                    ti.lm.procLock.lock();
                    t.start();
                    ti.lm.lock();
                } catch (InterruptedException ie) {
                } finally {
                    ti.lm.procLock.unlock();
                }
            } catch (Exception ex) {
                System.err.println("Exception");
            }
            return ti.value;
        }
    
        /**
         * Constructor
         * 
         * @param prompt
         */
        public TextInput(String prompt) {
            this.lm = new LockMechanism();
            this.prompt = prompt;
        }
    
        /**
         *
         */
        public void run() {
            JLabel label = new JLabel(prompt, JLabel.LEFT);
            final JFrame frame = new JFrame();
            final JTextField jTextField = new JTextField(10);
            JButton button = new JButton("Submit");
    
            button.addActionListener(new ActionListener() {
    
                //button gets clicked
                public void actionPerformed(ActionEvent e) {
                    //get the value from the textfield
                    value = jTextField.getText();
                    //resume main thread
                    lm.unLock();
                    //close the gui
                    frame.dispose();
                }
            });
    
            Box box = new Box(BoxLayout.Y_AXIS);
            box.add(label);
            box.add(jTextField);
            box.add(button);
    
            frame.getContentPane().add(box);
            frame.pack();
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.setVisible(true);
        }
    
        class LockMechanism {
    
            public Lock procLock = null;
            public Condition processing = null;
            public boolean canProcess;
    
            public LockMechanism() {
                this.procLock = new ReentrantLock();
                this.processing = procLock.newCondition();
                this.canProcess = false;
            }
    
            /**
             * Pause the current thread
             *
             * @throws InterruptedException
             */
            public void lock() throws InterruptedException {
                while (!canProcess) {
                    processing.await();
                }
            }
    
            /**
             * Resume the the thread that is blocked by the lock
             */
            public void unLock() {
                canProcess = true;
                try {
                    processing.signalAll();
                } catch (IllegalMonitorStateException imse) {
                    System.err.println("IllegalMonitorStateException");
                } catch (Exception e) {
                    System.err.println(e.getMessage());
                }
            }
    
        }
    }

  2. #2
    Join Date
    May 2006
    Location
    UK
    Posts
    4,474

    Re: Prompt for value in swing thread

    Can you explain what you are trying to achieve as this seems like a hellishly complex way of getting the main thread to wait for a value to be input.
    Posting code? Use code tags like this: [code]...Your code here...[/code]
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