本题的功能是用文本框来设定表盘中指针的位置。窗口中有一个画板和两个文本框，画板中绘制了一个表盘和时针、分针，通过文本框分别设定“时”和“分”，表盘中的时针和分针就会指到对应的位置上。
import java. awt. * ;
import java. awt. event. * ;
import java. awt. geom. * ;
import javax. swing. * ;
import javax. swing, event. * ;
public class java3
public static void main(String[] args)
TextTestFrame frame=new TextTestFrame();
frame. setDefaultCloseOperation (JFrame. EXIT_ON_CLOSE);
frame. show();
class TextTestFrame extends JFrame
public TextTestFrame()
setTitle("java3");
setSize(DEFAULT_WIDTH, DEFAULT_HEIGHT);
Container contentPane=getContentPane();
DocumentListener listener=new DocumentListen-er();
JPanel panel=new JPanel();
hourField=new JTextField("12",3);
panel, add(hourField);
hourField, getDocument (). addDocumentListener(this);
minuteField=new JTextField("00",3);
panel, add(minuteField);
minuteField, getDocument(), addDocumentListener(listener);
contentPane, add ( panel, BorderLayout. SOUTH);
clock=new ClockPanel();
contentPane, add (clock, BorderLayout. CENTER);
public void setClock()
try
int hours
= Integer. parseInt (hourField. getText(). trim());
int minutes
= Integer. parselnt(minuteField, getText(), trim());
clock, setTime(hours, minutes);
catch (NumberFormatException e)
public static final int DEFAULT WIDTH=300;
public static final int DEFAULT_HEIGHT=300;
private JTextField hourField;
private JTextField minuteField;
private ClockPanel clock;
private class clockFieldListener extends DocumentListener
public void insertUpdate(DocumentEvent e) setClock();
public void removeUpdate(DocumentEvent e) setClock();
public void changedUpdate(DocumentEvent e)
class ClockPanel extends JPanel
public void paintComponent(Graphics g)
super, paintComponent(g);
Graphics2D g2=(Graphics2D)g;
Ellipse2D circle
=new Ellipse2D. Double(0,0,2 * RADIUS, 2 * RADIUS);
g2. draw(circle);
double hourAngle
=Math. toRadians(90-360 * minutes/(12 * 60));
drawHand (g2, hourAngle, HOUR_HAND_LENGTH);
double minuteAngle
Math. toRadians(90-360 * minutes/60)
drawHand(g2, minuteAngle, MINUTE_HAND_LENGTH);
public void drawHand(Graphics2D g2,
double angle, double handLength)
Point2D end=new Point2D. Double(
RADIUS+handLength * Math. cos(angle),
RADIUS-handLength * Math. sin(angle));
Point2D center=new Point2D. Double(RADIUS, RADIUS)
g2. draw(new Line2D. Double(center, end));
public void setTime(int h, int m)
minutes=h*60+m;
repaint();
private double minutes=0;
private double RADIUS=100;
private double MINUTE_HAND_LENGTH=0.8 * RADIUS;
private double HOUR_HAND_LENGTH=0.6 * RADIUS;
CuSO4＋SO2↑＋2H2O，对于该反应，下列说法中不正确的是