JAVA做的一个学生成绩系统

import java.applet.Applet;
import java.awt.*;
import java.awt.event.*;
import java.util.*;
import java.lang.*;

public class Students extends Applet implements ActionListener
{
 Vector StuInf=new Vector();
 StudentInf SI;
 String xm;
 String bj;
 int i,j,xh,cj;
 static int mid;
 Label prompt1=new Label("学生成绩管理系统");
 Label prompt2=new Label("   用户:");
 Label prompt3=new Label("   密码:");
 Label prompt4=new Label("   班级:");
 Label prompt5=new Label("   成绩:");
 TextField input1=new TextField(8);
 TextField input2=new TextField(8);
 TextField input3=new TextField(8);
 TextField input4=new TextField(8);
 Button btn1=new Button("登录");
 Button btn2=new Button("增加");
 Button btn3=new Button("修改");
 Button btn4=new Button("删除");
 
 public void init()
 {
  setLayout(new GridLayout(6,3));
  add(new Label());
  add(prompt1);
  add(new Label());
  add(prompt2);
  add(input1);
  add(new Label());
  add(prompt3);
  add(input2);
  add(btn1);
  add(prompt4);
  add(input3);
  add(new Label());
  add(prompt5);
  add(input4);
  add(new Label());
  add(btn2);
  add(btn3);
  add(btn4);
  prompt4.setVisible(false);
  prompt5.setVisible(false);
  input3.setVisible(false);
  input4.setVisible(false);
  btn2.setVisible(false);
  btn3.setVisible(false);
  btn4.setVisible(false);
  btn1.addActionListener(this);
  btn2.addActionListener(this);
  btn3.addActionListener(this);
  btn4.addActionListener(this);
 }
 public void actionPerformed(ActionEvent e)
 {
  if(e.getActionCommand()=="登录")
  {
   String a,b;
   a=input1.getText();
   b=input2.getText();
   input1.setText("");
   if((a.equals("12")==true)&&(b.equals("12")==true))
   {
    prompt2.setText("   姓名:");
    prompt3.setText("   学号:"); 
    prompt4.setVisible(true);
    prompt5.setVisible(true);
    input3.setVisible(true);
    input4.setVisible(true);
    btn2.setVisible(true);
    btn3.setVisible(true);
    btn4.setVisible(true);
    btn3.setEnabled(false);
    btn4.setEnabled(false);
    btn1.setLabel("查询");
    input1.setText("登录成功");
    input1.selectAll();
   }
   else
   input2.setText("用户名或密码错");
  }
  if(e.getActionCommand()=="增加")
  {
   boolean scucss=true;
   try
   {
    XingMing();
   }
   catch(EmptyException as)
   {
    input1.setText("姓名不能为空");
    scucss=false;
   }
   try
   {
    xh=Integer.parseInt(input2.getText());
   }
   catch(NumberFormatException m)
   {
    input2.setText("学号为空或格式错");
    scucss=false;
   } 
   bj=input3.getText();
   try
   {
    ChengJi();
   }
   catch(EmptyException as)
   {
    cj=-1;
   }
   catch(OverException dd)
   {
    input4.setText("应在0-100间");
    scucss=false;
   }
   catch(NumberFormatException cm)
   {
    input4.setText("成绩应为数据");
    scucss=false;  
   }
   if(scucss==true)
   {
   SI=new StudentInf(xm,xh,bj,cj);
   Insert(SI);
   }
  }
  if(e.getActionCommand()=="修改")
  {
   xm=input1.getText();
   xh=Integer.parseInt(input2.getText());
   bj=input3.getText();
   cj=Integer.parseInt(input4.getText());
   SI=new StudentInf(xm,xh,bj,cj);
   StuInf.setElementAt(SI, mid);
   btn3.setEnabled(false);
  }
  if(e.getActionCommand()=="删除")
  {
   StuInf.removeElementAt(mid); 
   btn4.setEnabled(false);
   input1.setText("删除成功");
   input2.setText("");
   input3.setText("");
   input4.setText("");
  }
  if(e.getActionCommand()=="查询")
  {
   boolean right=true;
   try
   {
    xh=Integer.parseInt(input2.getText());
   }
   catch(NumberFormatException m)
   {
    input2.setText("学号为空或格式错");
    right=false;
   } 
   if(right==true)
   {
    search(xh);
    btn3.setEnabled(true);
    btn4.setEnabled(true);
   }
  }
  
 }
 //查找方法
 public void search(int k)
 {
   boolean  exist=false;
   int low=0;
   int high=StuInf.size()-1;
   while(low<=high)
   {
    mid=(high+low)/2;
    StudentInf a1=(StudentInf) StuInf.elementAt(mid);
    if(a1.getStuNo()==k)
    {
     SI=(StudentInf) StuInf.elementAt(mid);
     String x = String.valueOf(SI.getStuNo());
     exist=true;
     input1.setText(SI.getname());
     input1.selectAll();
     input2.setText("0"+x);
     input3.setText(SI.getClassNo());
     if(SI.getLevel()==-1)
      input4.setText("未参加考试");
     else
     {
      String y = String.valueOf(SI.getLevel());
      input4.setText(y);
     }
     break;
    }
    else if(a1.getStuNo()<k)
    low=mid+1;
    else
    high=mid-1; 
   }
   if(exist==false)
   {
    input1.setText("无此学号学生信息");
    input1.selectAll();
   }
 }
//添加方法
 public void Insert(StudentInf q)
 {
  int i=0;
  
  if(StuInf.isEmpty()==true) 
   {
    StuInf.addElement(q);
    input1.setText("");
    input2.setText("");
    input3.setText("");
    input4.setText("");
   }
  else
  {
   StudentInf xh;
   xh=(StudentInf) StuInf.firstElement();
   while(xh.getStuNo()<q.getStuNo())
   {
    i++;
    if(i<StuInf.size())
    xh=(StudentInf) StuInf.elementAt(i);
    else 
    break;
   }   
   if(xh.getStuNo()==q.getStuNo())
   {
    input2.setText("此学生信息已存在");
    input2.requestFocus();
    input2.selectAll();
   }
   else 
   {
    StuInf.insertElementAt(q,i);  
    input1.setText("");
    input2.setText("");
    input3.setText("");
    input4.setText("");
   }
  }  
 }
 
 //异常类
 class OverException extends Exception
 {
  String over;
 } 
 class EmptyException extends Exception
 {
  String empty;
 }
 void XingMing() throws EmptyException
 {
  if((input1.getText()).equals(""))
   throw (new EmptyException());
  else
   xm=input1.getText();
 }
 void ChengJi() throws OverException,EmptyException 
 {
  if((input4.getText()).equals(""))
  throw(new EmptyException());
  else
  cj=Integer.parseInt(input4.getText());
  if(cj<0||cj>100)
  throw (new  OverException());
 }
 
 //学生信息类
 public class StudentInf
 {
  private String name;
  private int StuNo;
  private String ClassNo;
  private int Level;
  StudentInf(String xingming,int xuehao,String banji,int chengji)
  {
   name=xingming;
   StuNo=xuehao;
   ClassNo=banji;
   Level=chengji;
  }
  public int getStuNo()
  {
   return StuNo;
  }
  public String getname()
  {
   return name;
  }
  public String getClassNo()
  {
   return ClassNo;
  }
  public int getLevel()
  {
   return Level;
  }
 }

}