在eclipse中运行没错,但是,放进html文件中,运行就有错误了并且提示:异常:java.lang.NullPointerException我的代码:
package nwsuaf.cie.ym.diy;import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import java.applet.Applet;
import java.awt.*;public class MyCheckbox extends Applet implements ItemListener {
Checkbox c1,c2,c3;
Color c = new Color(200,180,100);
int b = 0;
int red=0,green = 0,blue = 0;
public void init()
{
c1 = new Checkbox("Red");
c1.addItemListener(this);
add(c1);
c2 = new Checkbox("Green");
c2.addItemListener(this);
add(c2);
c3 = new Checkbox("Blue");
c3.addItemListener(this);
add(c3);
}
public void paint(Graphics g)
{
setBackground(c); //设置背景颜色
g.setColor(new Color(red,green,blue));
/* if(b == 1)
g.setColor(new Color(255,0,0));
else if(b==2)
g.setColor(new Color(0,255,0));
*/
g.fill3DRect(40,40,100,100,true);
}
public void itemStateChanged(ItemEvent arg0) {
// TODO Auto-generated method stub
if(c1.getState())
red = 255;
else
red = 0;
if(c2.getState())
green = 255;
else
green = 0;
if(c3.getState())
blue = 255;
else
blue = 0;
repaint();
}}
package nwsuaf.cie.ym.diy;import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import java.applet.Applet;
import java.awt.*;public class MyCheckbox extends Applet implements ItemListener {
Checkbox c1,c2,c3;
Color c = new Color(200,180,100);
int b = 0;
int red=0,green = 0,blue = 0;
public void init()
{
c1 = new Checkbox("Red");
c1.addItemListener(this);
add(c1);
c2 = new Checkbox("Green");
c2.addItemListener(this);
add(c2);
c3 = new Checkbox("Blue");
c3.addItemListener(this);
add(c3);
}
public void paint(Graphics g)
{
setBackground(c); //设置背景颜色
g.setColor(new Color(red,green,blue));
/* if(b == 1)
g.setColor(new Color(255,0,0));
else if(b==2)
g.setColor(new Color(0,255,0));
*/
g.fill3DRect(40,40,100,100,true);
}
public void itemStateChanged(ItemEvent arg0) {
// TODO Auto-generated method stub
if(c1.getState())
red = 255;
else
red = 0;
if(c2.getState())
green = 255;
else
green = 0;
if(c3.getState())
blue = 255;
else
blue = 0;
repaint();
}}
<APPLET CODE="MyCheckbox.class" WIDTH=200 HEIGHT=150>
</APPLET>
</HTML>
或者在在html中写:nwsuaf.cie.ym.diy.MyCheckbox",然后在html文件目录下建立目录/nwsuaf/cie/ym/diy/,将class文件放入其中
我今天上Java课,也刚好学到了包,于是上课时我也想是不是因为包的原因