driver.java

Java程序设计(美) David D. Riley著 机械工业出版社 书籍配套 代码

import javax.swing.*;
import java.awt.TextArea;

/** Program to measure distance traveled due to gravity (Figure 10.13)
 *  Author: David Riley
 *  Date: January, 2005
 */
public class Driver  {
    private JFrame window;
    private TextArea outPane;
    private HeightField inField;
    private JLabel label;

    /** post:   window != null  and  outPane != null  and  inField!=null
     *          and  outPane, inField are both displayed in window  
     */
    public Driver()   {
        window = new JFrame("Gravity Demo"); 
        window.setBounds(10, 10, 400, 230);
        window.setVisible(true);
        window.setLayout(null);
        outPane = new TextArea();
        outPane.setBounds(50, 50, 340, 150);
        window.add(outPane, 0);
        label = new JLabel("Initial Height:");
        label.setBounds(10, 10, 100, 25);
        window.add(label, 0);
        inField = new HeightField(110, 10, this);
        window.add(inField, 0);
        window.repaint();
    }
    
    /** pre:    h > 0  and  outPane != null  <br>
     *  post:   outPane is reset to contain one line for each second of 
     *          drop from a height of h until through last height before 
     *          zero.  Each line gives the height of the dropped object 
     *          and its velocity at that second.   
     */
    public void displayFall( int h )   {
        int  seconds;
        outPane.setText("");   // clear the text area of prior content
        seconds = 0;
        while ( h-seconds*seconds*4.9 > 0 )   {
            outPane.append("Time: " + seconds +" sec.   ");
            outPane.append("Height: "+(int)(h-seconds*seconds*4.9)+"m.");
            outPane.append("   Velocity: " + seconds*9.81 + "\n");
            seconds++;
        }
        outPane.repaint();
    }
}