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

public class Student extends JApplet implements ActionListener
{
JLabel l1,l2,l3,l4;
JTextField t1,t2,t3,t4;
JButton bt;
JPanel p1,p2;

public void init()
{
l1=new JLabel("学生平时考试成绩");
l1=new JLabel("学生机试成绩");
l1=new JLabel("学生笔试成绩");
l1=new JLabel("学生总评成绩");

t1=new JTextField(30);
t2=new JTextField(30);
t3=new JTextField(30);
t4=new JTextField(30);
t4.setEditable(false);

bt=new JButton("计算学生总评成绩");
bt.addActionListener(this);

p1=new JPanel(new GridLayout(4,2,2,2));
p2=new JPanel();

p1.add(l1);p1.add(t1);
p1.add(l2);p1.add(t2);
p1.add(l3);p1.add(t3);
p1.add(l4);p1.add(t4);
p2.add(bt);

this.getContentPane().setLayout(new BorderLayout());
this.getContentPane().add(p1,BorderLayout.NORTH);
this.getContentPane().add(p2,BorderLayout.SOUTH);
}

public void actionPerformed(ActionEvent ae)
{
double a,b,c,d;
try
{
if(t1.getText().equals("")||t2.getText().equals("")||t3.getText().equals(""))
{
JOptionPane.showMessageDialog(this,"空值","错误",JOptionPane.ERROR_MESSAGE);
t4.setText("");
}
else
{
a=Double.parseDouble(t1.getText());
b=Double.parseDouble(t2.getText());
c=Double.parseDouble(t3.getText());
if(a<0||b<0||c<0||a>100||b>100||c>100)
{
t4.setText("输入的数值必须在0-100之间");
}
else
{
d=a*0.2+b*0.2+c*0.4;
String str=String.valueOf(d);
str=str.substring(0,str.indexOf(".")+1);
t4.setText(str);
}
}
}

catch(Exception e)
{
t4.setText("错误");
}
}
}