Java 小程序无法清除屏幕上的文本

Question

所以我在下面有这段代码，我正在尝试刷新屏幕上的文本以显示当前时间。到目前为止，我已经尝试使用 drawRect 作为一种清除方式，但文本会保留在那里，而不是更新。 super.paint 也没有用。另外，我会将该新语句合并到 init() 或 paint() 方法中吗？

import java.awt.*;
import java.util.*;
import java.util.concurrent.TimeUnit;
import java.awt.*;
import java.awt.font.*;

import javax.swing.*;

import java.awt.geom.*;
public class HelloWorldApplet extends javax.swing.JApplet {
Calendar now = Calendar.getInstance();
int second = now.get(Calendar.SECOND);
int hour = now.get(Calendar.HOUR_OF_DAY);
int minute = now.get(Calendar.MINUTE);
int month = now.get(Calendar.MONTH) + 1;
int day = now.get(Calendar.DAY_OF_MONTH);
int year = now.get(Calendar.YEAR);
String greeting;
String currentTime = ("The time currently is: " + hour + ":" + minute + " and" + second + " seconds");
String currentDate = ("Date: " + month + "/" + day + "/" + year);


public void init() {
    greeting = "Hello World";
     Font myFont = new Font("TimesRoman", Font.BOLD, 20);
     // set the component or graphics object like this:
     setFont(myFont);

}
public void paint(Graphics screen){

        Graphics2D screen2D = (Graphics2D) screen;
        screen2D.drawString(greeting, 20, 50);
        screen2D.drawString(currentTime, 20, 75);
        screen2D.drawString(currentDate, 20, 100);
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
        //DoNothing. Pretend it didnt happen...
        } 




}
public void setup(Graphics screen) {
    for (int x = 1; x < 2000000000;) {
        x++;
        repaint();

}
}

}

Answer 1

_{@trashgod 已经解释了最重要的事情，但我会在我的回答中重复它们以便更完整}

覆盖 paintComponent()，而不是 paint()
创建一个新的 JPanel class 为您绘画
在你的paintComponent()方法中获取时间，否则它将始终保持不变
使用计时器而不是休眠事件调度线程
调用super.paintComponent()清屏

固定代码如下：

import java.awt.*;
import java.util.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JPanel;
import javax.swing.Timer;


public class HelloWorldApplet extends javax.swing.JApplet {

    String greeting;

    Font myFont = new Font("Times New Roman", Font.BOLD, 20);

    public void init() {

        greeting = "Hello World";

        add(new MyPanel());

        ActionListener actionListener = new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {

                repaint();

            }       
        };

        Timer timer = new Timer(500, actionListener);
        timer.start();


    }

    class MyPanel extends JPanel {

        public void paintComponent(Graphics screen) {

            super.paintComponent(screen);

            Calendar now = Calendar.getInstance();
            int second = now.get(Calendar.SECOND);
            int hour = now.get(Calendar.HOUR_OF_DAY);
            int minute = now.get(Calendar.MINUTE);
            int month = now.get(Calendar.MONTH) + 1;
            int day = now.get(Calendar.DAY_OF_MONTH);
            int year = now.get(Calendar.YEAR);

            String currentTime = ("The time currently is: " + hour + ":" + minute
                    + " and " + second + " seconds");
            String currentDate = ("Date: " + month + "/" + day + "/" + year);

            setFont(myFont);

            Graphics2D screen2D = (Graphics2D) screen;
            screen2D.drawString(greeting, 20, 50);
            screen2D.drawString(currentTime, 20, 75);
            screen2D.drawString(currentDate, 20, 100);

        }

    }


}

Java 小程序无法清除屏幕上的文本

Java Applet failing to clear text onscreen

java

swing

applet