问答题

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.setDefauhCloseOperation(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 DocurnentListener();
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.parseInt(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 Poim2D.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;