线程通信：如何发出信号，表明已单击某个键？ java.lang.IllegalMonitorStateException

Question

i have a simple JavaFX stage with a TextField. What i want to do is: when user inserts letters into the TextField, i want to print "now" (just to look if it works). Im using a Thread because later i want to scan a dictonary to see, if the letters the user entered are part of words from the dictionary.

But i get: java.lang.IllegalMonitorStateException

Any ideas? I don't seem to understand the whole concept of Condition.await and Multithreading..

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.TextField;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class DictionaryThreading extends Application {


private static Lock lock = new ReentrantLock();
public static Condition condition = lock.newCondition();

public static void main(String[] args) {
    launch();
}

private static class ScanWords implements Runnable{

    @Override
    public void run() {
        lock.lock();
        try{    
            while(true){
                this.wait();
                System.out.println("clicked");
            }
        } catch (Exception e){
            e.printStackTrace();
        } finally{
            lock.unlock();
        }   
    }

}

@Override
public void start(Stage primaryStage) throws Exception {
    StackPane pane = new StackPane();

    new ScanWords().run();
    TextField tf = new TextField("Please enter a word");
    tf.setOnKeyPressed(e -> {});
    pane.getChildren().add(tf);

    Scene scene = new Scene(pane);
    primaryStage.setScene(scene);
    primaryStage.show();

}

}

Answer 1

There is no need to create a thread that does nothing other than wait for user events. The JavaFX framework already provides this for you (it is one of the fundamental pieces of functionality of any UI toolkit). All you need to do to respond to changes in the text in a text field is register a change listener with the text field's text property:

public void start(Stage primaryStage) throws Exception {
    StackPane pane = new StackPane();

    TextField tf = new TextField("Please enter a word");
    tf.textProperty().addListener((obs, oldText, newText) -> {
        System.out.println("text changed");
    });
    pane.getChildren().add(tf);

    Scene scene = new Scene(pane);
    primaryStage.setScene(scene);
    primaryStage.show();

}

If the thing you need to do in response to the text changing takes a long time, then you should launch that process in a background thread in the listener on the text field. If you are searching something large, you probably want to cancel any existing search, so that you don't end up with a large number of searches all running concurrently. The JavaFX Service class provides the functionality you need for this:

public class SearchService extends Service<List<String>> {

    // modify and access only on FX Application Thread:
    private String searchString ;

    @Override
    protected Task<List<String>> createTask() {
        final String s = searchString ;
        return new Task<List<String>>() {
            @Override
            protected List<String> call() throws Exception {
                List<String> matches = new ArrayList<>();
                // do search for strings matching s
                // be sure to check isCancelled() regularly
                return matches ;
            }
        };
    }

    public String getSearchString() {
        checkThread();
        return searchString ;
    }

    public void setSearchString(String searchString) {
        checkThread();
        this.searchString = searchString ;
    }

    private void checkThread() {
        if (! Platform.isFxApplicationThread()) {
            throw new IllegalStateException("Not on FX Application Thread");
        }
    }
}

Then you can do

public void start(Stage primaryStage) throws Exception {
    StackPane pane = new StackPane();

    SearchService searchService = new SearchService();

    searchService.setOnSucceeded(e -> {
        List<String> matches = searchService.getValue();
        // do whatever you need with search results...
        // this is called on FX application thread
    });

    TextField tf = new TextField("Please enter a word");
    tf.textProperty().addListener((obs, oldText, newText) -> {
        searchService.cancel();
        searchService.setSearchText(newText);
        searchService.restart();
    });
    pane.getChildren().add(tf);

    Scene scene = new Scene(pane);
    primaryStage.setScene(scene);
    primaryStage.show();

}

Answer 2

I don't use JavaFX, but I think you need to use EventListener . Try to use TextListener or InputMethodListener . For example:

StackPane pane = new StackPane();

TextField tf = new TextField("Please enter a word");

tf.addTextListener(e -> System.out.println("Pushed"));

pane.getChildren().add(tf);

Scene scene = new Scene(pane);
primaryStage.setScene(scene);
primaryStage.show();

Answer 3

wait method should be executed within synchronized block:

    try{    
        while(true){
            synchronized(this){
                this.wait();
                System.out.println("clicked");
            }
        }
    } catch (Exception e){
        e.printStackTrace();
    } finally{
        lock.unlock();
    }