stillclock.java

java程序设计导论（daniel liang著） 所有偶数课后习题答案

// StillClock.java: Display a clock in JPanel
import java.awt.*;
import javax.swing.*;
import java.util.*;

public class StillClock extends JPanel {
  private int hour;
  private int minute;
  private int second;

  /** Construct a defauktdefault clock with the current time*/
  public StillClock() {
    setCurrentTime();
  }

  /** Construct a clock */
  public StillClock(int hour, int minute, int second) {
    this.hour = hour;
    this.minute = minute;
    this.second = second;
  }

  /** Return hour */
  public int getHour() {
    return hour;
  }

  /** Set a new hour */
  public void setHour(int hour) {
    this.hour = hour;
    repaint();
  }

  /** Return minute */
  public int getMinute() {
    return minute;
  }

  /** Set a new minute */
  public void setMinute(int minute) {
    this.minute = minute;
    repaint();
  }

  /** Return second */
  public int getSecond() {
    return second;
  }

  /** Set a new second */
  public void setSecond(int second) {
    this.second = second;
    repaint();
  }

  /** Draw the clock */
  protected void paintComponent(Graphics g) {
    super.paintComponent(g);

    // Initialize clock parameters
    int clockRadius =
      (int)(Math.min(getWidth(), getHeight()) * 0.8 * 0.5);
    int xCenter = getWidth() / 2;
    int yCenter = getHeight() / 2;

    // Draw circle
    g.setColor(Color.black);
    g.drawOval(xCenter - clockRadius, yCenter - clockRadius,
      2 * clockRadius, 2 * clockRadius);
    g.drawString("12", xCenter - 5, yCenter - clockRadius + 12);
    g.drawString("9", xCenter - clockRadius + 3, yCenter + 5);
    g.drawString("3", xCenter + clockRadius - 10, yCenter + 3);
    g.drawString("6", xCenter - 3, yCenter + clockRadius - 3);

    // Draw second hand
    int sLength = (int)(clockRadius * 0.8);
    int xSecond = (int)(xCenter + sLength *
      Math.sin(second * (2 * Math.PI / 60)));
    int ySecond = (int)(yCenter - sLength *
      Math.cos(second * (2 * Math.PI / 60)));
    g.setColor(Color.red);
    g.drawLine(xCenter, yCenter, xSecond, ySecond);

    // Draw minute hand
    int mLength = (int)(clockRadius * 0.65);
    int xMinute = (int)(xCenter + mLength *
      Math.sin(minute * (2 * Math.PI / 60)));
    int yMinute = (int)(yCenter - mLength *
      Math.cos(minute * (2 * Math.PI / 60)));
    g.setColor(Color.blue);
    g.drawLine(xCenter, yCenter, xMinute, yMinute);

    // Draw hour hand
    int hLength = (int)(clockRadius * 0.5);
    int xHour = (int)(xCenter + hLength *
      Math.sin((hour % 12 + minute / 60.0) * (2 * Math.PI / 12)));
    int yHour = (int)(yCenter - hLength *
      Math.cos((hour % 12 + minute / 60.0) * (2 * Math.PI / 12)));
    g.setColor(Color.green);
    g.drawLine(xCenter, yCenter, xHour, yHour);
  }

  public void setCurrentTime() {
    // Construct a calendar for the current date and time
    Calendar calendar = new GregorianCalendar();

    // Set current hour, minute and second
    this.hour = calendar.get(Calendar.HOUR_OF_DAY);
    this.minute = calendar.get(Calendar.MINUTE);
    this.second = calendar.get(Calendar.SECOND);
  }

  public Dimension getPreferredSize() {
    return new Dimension(200, 200);
  }
}