程序是这样的,不知道哪里没有初始化,可以生成class文件,只是执行的时候出现上面的提示。import java.util.*;import java.awt.*;
import java.applet.*;import java.awt.event.*;
public class Example9_5 extends Applet implements TextListener
{TextArea text1,text2;
public void init()
{ text1=new TextArea(6,15);
text2=new TextArea(6,15);
add(text1);add(text2);
text1.addTextListener(this);
text2.setEditable(false);
}
public void textValueChanged(TextEvent e)
{if(e.getSource()==text1)
{String s=text1.getText();
StringTokenizer fenxi=new StringTokenizer(s,",'\n'");
int n=fenxi.countTokens();
String a[]=new String[n];
for(int i=0;i<=n-1;i++)
{String temp=fenxi.nextToken();
a[i]=temp;
}
for(int i=0;i<=n-1;i++)//按字典序从小到大排序
{for(int j=i+1;j<=n-1;j++)
{if(a[j].compareTo(a[i])<0)
{String t=a[j];a[j]=a[i];a[i]=t;
}
}
}
text2.setText(null);//刷新显示
for(int i=1;i<n;i++)
{text2.append(a[i]+"\n");
}
}
}
}
import java.applet.*;import java.awt.event.*;
public class Example9_5 extends Applet implements TextListener
{TextArea text1,text2;
public void init()
{ text1=new TextArea(6,15);
text2=new TextArea(6,15);
add(text1);add(text2);
text1.addTextListener(this);
text2.setEditable(false);
}
public void textValueChanged(TextEvent e)
{if(e.getSource()==text1)
{String s=text1.getText();
StringTokenizer fenxi=new StringTokenizer(s,",'\n'");
int n=fenxi.countTokens();
String a[]=new String[n];
for(int i=0;i<=n-1;i++)
{String temp=fenxi.nextToken();
a[i]=temp;
}
for(int i=0;i<=n-1;i++)//按字典序从小到大排序
{for(int j=i+1;j<=n-1;j++)
{if(a[j].compareTo(a[i])<0)
{String t=a[j];a[j]=a[i];a[i]=t;
}
}
}
text2.setText(null);//刷新显示
for(int i=1;i<n;i++)
{text2.append(a[i]+"\n");
}
}
}
}
import java.applet.*;import java.awt.event.*;
public class Example9_5 extends Applet implements TextListener
{TextArea text1,text2;
public void init()
{ text1=new TextArea(6,15);
text2=new TextArea(6,15);
add(text1);add(text2);
text1.addTextListener(this);
text2.setEditable(false);
}
public void textValueChanged(TextEvent e)
{if(e.getSource()==text1)
{String s=text1.getText();
StringTokenizer fenxi=new StringTokenizer(s,",'\n'");
int n=fenxi.countTokens();
String a[]=new String[n];
for(int i=0;i<=n-1;i++)
{String temp=fenxi.nextToken();
a[i]=temp;
}
for(int i=0;i<=n-1;i++)//按字典序从小到大排序
{for(int j=i+1;j<=n-1;j++)
{if(a[j].compareTo(a[i])<0)
{String t=a[j];a[j]=a[i];a[i]=t;
}
}
}
text2.setText(null);//刷新显示
for(int i=1;i<n;i++)
{text2.append(a[i]+"\n");
}
}
}
}
at Example12_3.init(Example12_3.java:33)是Example12_3.java你给的程序却是
public class Example9_5是不是贴错了?
我的可以生成class文件,可是不能用appletviewer运行。
import java.applet.*;import java.awt.*;import java.awt.event.*;
class Mycanvas extends Canvas
{int x,y;
Mycanvas(int a,int b)
{x=a;y=b;
setSize(100,160);
}
public void paint(Graphics g)
{g.setColor(Color.red);
g.fillOval(50,50,4*x,4*y);
g.drawString("我是第"+x,10,150);
}
}
public class Example12_3 extends Applet implements ActionListener
{CardLayout mycard;
Button button1,button2,button3;
Mycanvas mycanvas[];
Panel p;
public void init()
{setLayout(new BorderLayout());
mycard=new CardLayout();
p=new Panel();
p.setLayout(mycard);
button1=new Button("this");
button1=new Button("next");
button1=new Button("last one");
mycanvas=new Mycanvas[21];
for(int i=1;i<=20;i++)
{mycanvas[i]=new Mycanvas(i,i);
p.add("i am"+i,mycanvas[i]);
}
button1.addActionListener(this);
button2.addActionListener(this);
button3.addActionListener(this);
Panel p2=new Panel();
p2.add(button1);p2.add(button2);p2.add(button3);
add(p,BorderLayout.CENTER);add(p2,BorderLayout.SOUTH);
}
public void actionPerformed(ActionEvent e)
{if(e.getSource()==button1)
{mycard.first(p);}
else if(e.getSource()==button2)
{mycard.next(p);}
else if(e.getSource()==button3)
{mycard.last(p);
}
}
}
java.lang.NullPointerException
at Example12_3.init(Example12_3.java:33)
at sun.applet.AppletPanel.run(AppletPanel.java:353)
at java.lang.Thread.run(Thread.java:534)
说明是Example12_3.java:33
33行错,那是button2没有建立实例button1=new Button("this");
button1=new Button("next");
button1=new Button("last one");应该是
button1=new Button("this");
button2=new Button("next");
button3=new Button("last one");把,估计拷贝后忘记改了