creditscroller.java~

书籍"Java_面向事件编程"的附带光盘代码

import objectdraw.*;
import java.awt.*;

public class CreditScroller extends ActiveObject {
    
    private static final int DELAY_TIME = 500;
    private static final int GAP_SIZE = 20;

    private DrawingCanvas canvas;
    
    public CreditScroller(DrawingCanvas aCanvas) {
        canvas = aCanvas;
        start();
    }
    
    public void run() {
        Credit lastCredit;
        lastCredit = new Credit("Producer . . . Martha Washington", canvas);
        waitToScroll(lastCredit);
        lastCredit = new Credit("Director . . . George Washington", canvas);
        waitToScroll(lastCredit);
        lastCredit = new Credit("Script . . . Thomas Jefferson", canvas);
        waitToScroll(lastCredit);
        lastCredit = new Credit("Costumes . . . Betsy Ross", canvas);
    }

    private boolean tooClose (Credit lastCredit, int desiredGap) {
        return lastCredit.distanceTraveled () <
                                 desiredGap + lastCredit.getHeight();
    }

    private void waitToScroll(Credit aCredit) {
        while (tooClose(aCredit, GAP_SIZE)) {
            pause(DELAY_TIME);
        }
    }

}