package applet;

import java.applet.*;
import java.awt.*;

public class Exam6_4 extends Applet {
    /**
     * 
     */
    private static final long serialVersionUID = 7453078616621241814L;

    int x;
    int y;

    public void init() {

        x = Integer.parseInt(getParameter("x"));
        y = Integer.parseInt(getParameter("y"));
    }

    public void paint(Graphics g) {
        g.drawString("hello world", x, y);
    }
}

错误信息如下。哪位大神来看看
java.lang.NumberFormatException: null
    at java.lang.Integer.parseInt(Integer.java:542)
    at java.lang.Integer.parseInt(Integer.java:615)
    at applet.Exam6_4.init(Exam6_4.java:17)
    at sun.applet.AppletPanel.run(AppletPanel.java:434)
    at java.lang.Thread.run(Thread.java:745)