刷新JLabel

Question

我正在尝试在JFrame中显示当前时间。如何刷新JLabel中的文本，而不在每次必须更新文本时打开单独的框架？

这是我到目前为止的所有代码。

Test

public class Test{

    static String timeDisplay = "";

    public static class time extends Thread{
        static int timeHours = 7;
        static int timeMins = 30;
        static int timeSecs = 0;
        @Override
        public void run(){

            while(true){
                try{

                    time.sleep(1000);
                    timeSecs++;

                    if(timeSecs == 60){
                        timeMins++;
                        timeSecs = 0;
                    }
                    if(timeMins == 60){
                        timeHours++;
                        timeMins = 0;
                    }

                    if(timeHours < 10){
                        if(timeMins < 10){
                            if(timeSecs < 10){
                                timeDisplay = "0" + timeHours + ":" + "0" + timeMins + ":" + "0" + timeSecs;
                            }
                            else{
                                timeDisplay = "0" + timeHours + ":" + "0" + timeMins + ":" + timeSecs;
                            }
                        }
                        else{
                            if(timeSecs < 10){
                                timeDisplay = "0" + timeHours + ":" + timeMins + ":" + "0" + timeSecs;
                            }
                            else{
                                timeDisplay = "0" + timeHours + ":" + timeMins + ":" + timeSecs;
                            }
                        }
                    }
                    else{
                        if(timeMins < 10){
                            if(timeSecs < 10){
                                timeDisplay = timeHours + ":" + "0" + timeMins + ":" + "0" + timeSecs;
                            }
                            else{
                                timeDisplay = timeHours + ":" + "0" + timeMins + ":" + timeSecs;
                            }
                        }
                        else{
                            if(timeSecs < 10){
                                timeDisplay = timeHours + ":" + timeMins + ":" + "0" + timeSecs;
                            }
                            else{
                                timeDisplay = timeHours + ":" + timeMins + ":" + timeSecs;
                            }
                        }
                    }

                    System.out.println(timeDisplay);
                    //CountDown time = new CountDown(timeDisplay);


                }
                catch(Exception e){
                    System.out.println("Something went wrong :(");
                }
            }

        }

    }

    public static void main(String[] args){

        time time = new time();
        time.start();
            try {
                TimeUnit.SECONDS.sleep(1);
                CountDown window = new CountDown(timeDisplay);
                window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                window.setSize(500, 500);
                window.setVisible(true);
            }
            catch (Exception e) {
                e.printStackTrace();
            }

    }

}

CountDown

public class CountDown extends JFrame{

    private static final long serialVersionUID = 1L;

    static JLabel label = new JLabel();

    public CountDown(String time){

        super("Title");
        setLayout(new FlowLayout());

        add(label);
        label.setText("Current Time: " + time);

        Handler eventHandler = new Handler();

    }

    private class Handler implements ActionListener{

        public void actionPerformed(ActionEvent event){

            String string = "";

            if(event.getSource()==""){
                string = String.format("label 1: %s", event.getActionCommand());
            }

        }

    }

}

我对这个程序的意图是制作一个显示当前时间的帧。它使用的是程序中的本地时间，而不是实际时间。提前感谢，如果我应该修改代码中的任何内容以使其更好，请随时告诉我。

Answer 1

API文档将成为您的朋友。请看一下JLabel的文档，特别是setText()方法。可以在事件处理程序中再次使用此方法来更改标签的文本。

但另一个问题是，您既没有触发也没有注册事件，因此您编写的actionPerformed函数永远不会被调用。如果秒精度足够好，您可以使用javax.swing.Timer极大地简化代码。不需要在不必要的地方更改代码，这应该会让你走上正确的道路：

public class CountDown extends JFrame{

    private static final long serialVersionUID = 1L;

    private JLabel label = new JLabel(); // note: understand static keyword before using it.

    private long startTime = System.currentTimeMillis(); // gets the current time in milliseconds, when your class is initialized.

    public CountDown(String time){

        super("Title");
        setLayout(new FlowLayout());

        add(label);
        // label.setText("Current Time: " + time); "time" was never in scope here.

        Handler eventHandler = new Handler();
        new Timer(1000, eventHandler).start(); // will execute ~1/sec
    }

    private class Handler implements ActionListener{

        public void actionPerformed(ActionEvent event){

              // NOTE: here, you could put all of your logic that was previously
              // in your Thread to determine the time, then use the result
              // with label.setText();
              long currentTime = System.currentTimeMillis();

              long upTime = currentTime - startTime; // this is how many milliseconds your JFrame has been up and running.

              // TODO: formate upTime however you desire.

              label.setText( <whatever_you_calculate_directly_above> );
            }

        }

    }

}

你还需要重写main方法来初始化你的框架。这应该就行了。

public static void main( String[] args){
  JFrame frame = new CountDown(); 
  frame.setVisible(true);
}

如果main方法位于单独的文件中，则需要在该文件开头附近导入CountDown。

Answer 2

您应该首先创建一个CountDown实例，然后调用它的一个方法来设置标签的文本。

在CountDown中，您必须调用JLabel.setText。方法来设置标签的文本：

public void displayTime(String time){
   label.setText("Current Time: " + time);
}

用...and代替System.out.println(time)调用

time.displayTime(timeDisplay);

与其使用简单的线程，不如使用更适合gui对象的java.util.Timer，甚至更好的javax.swing.Timer。

另一个备注:类名以大写字母开头，而方法或变量以小写方法开头。

最后，你的处理程序在这里要做什么。你没有注册它，它似乎是无用的。