JavaFX : Use a Thread more than once

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天命终不由人
天命终不由人 2021-02-20 14:38

I\'m new with JavaFX and I\'ve a little problem with a thread: I can execute it twice and I can\'t find why.

Here is a sum-upt of my code:

Task

        
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3条回答
  • 2021-02-20 15:02

    With a button can fire new tasks

                        Button btn = new Button();
                        btn.setText("New task");
                        btn.setOnAction(new EventHandler<ActionEvent>() {
                            @Override
                            public void handle(ActionEvent event) {
                                Executor ex=new Executor("Task"+count);
                                ex.start();
                                count++;
                                System.out.println("Task  Starting...");
                            }
                        });
    
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  • 2021-02-20 15:20

    Do it with a wraper class

                import java.io.IOException;
                import javafx.concurrent.Task;
    
                public class Executor {
                    private String name;
                    private Task<Void> task;
    
                    public Executor(final String name) {
                        this.name=name;
                        task = new Task<Void>() {
                            @Override
                            public Void call() throws IOException, InterruptedException {
                                try {
                                    int i=0;
                                    while(i<20){
                                        System.out.println(name);
                                        Thread.sleep(2000);
                                        i++;
                                    }
                                    return null;
                                } catch (IllegalThreadStateException e) {
                                    System.out.println(e);
                                }
                                return null;
                            }
    
                            @Override
                            protected void succeeded() {
                                super.succeeded();
                                try {
                                    System.out.println(name+"  finish");
                                } catch (Exception ex) {
                                    System.out.println(ex);
                                }
                            }
                        };
                    }
    
                    public void start() {
                        try {
                                    Thread th = new Thread(task);
                                    th.start();
                                } catch (Exception ex) {
                                    System.out.println(ex);
                                }
                    }
                }
    
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  • 2021-02-20 15:23

    From the Thread.start() documentation : No

    It is never legal to start a thread more than once. In particular, a thread may not be restarted once it has completed execution.

    From the Concurrency in JavaFX tutorial :

    The Task class defines a one-time object that cannot be reused. If you need a reusable Worker object, use the Service class.

    So, you have to consider the Service class rather than Task.


    Edit: this should work for you:

    Service service = new Service<>(task);

    //Updated use this to create a new Service object instead
        Service service = new Service() {
        @Override
        protected Task createTask() {
            return new Task() {
                @Override
                protected Void call() throws Exception {
                    //Your codes here
                    return null;
                }
            };
        }
    };
    
    @FXML protected void launch(ActionEvent event){
         if (!service.isRunning()) {
            service.reset();
            service.start();
        }
    }
    
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