Exception in thread "main" java.lang.NullPointerException大神们这是什么问题
package learn;
import java.util.*; 
import java.io.*;
public class Tyg {

/**
* @param args
*/
public static void main(String[] args) throws Exception {
// TODO Auto-generated method stub
  EnMan en=new EnMan();
  BufferedReader re=new BufferedReader (new InputStreamReader(System.in));
  while(true){
  System.out.println("请选择你要进行的操作：");
  System.out.println("1：表示添加一个雇员");
  System.out.println("2: 表示显示一个雇员");
  System.out.println("3:表示修改一个雇员");
  System.out.println("4:表示删除一个雇员");
  System.out.print("5:表示退出系统");
  String operaType=re.readLine();
  if(operaType.equals("1")){
  System.out.println("雇员的名字为：");
  String name=re.readLine();
  System.out.println("雇员的编号为：");
  String no=re.readLine();
  System.out.println("雇员的薪水为：");
  float sal=Float.parseFloat(re.readLine());
  Emg em=new Emg(name,no,sal);
  en.addE(em);
   
   
  }  
  else if(operaType.equals("2")){
  System.out.println("请输入编号：");
  String no=re.readLine();
  en.showInfo(no);
   
  }
  else if(operaType.equals("3")){
  System.out.println("请输入编号：");
  String no=re.readLine();
  System.out.println("请输入薪水：");
  float newsal=Float.parseFloat(re.readLine());
  en.changeE(no, newsal);
   
   
  }
  else if(operaType.equals("4")){
  System.out.print("请输入编号：");
  String no=re.readLine();
  en.delE(no);
  }
  else if(operaType.equals("5")){
  System.exit(0);
  }
  }
   
   
}

}
class Emg
{
  private String name;
  private String no;
private float sal;
public Emg(String name,String no,Float sal)
{this.name=name;
this.no=no;
this.sal=sal;
 
  }
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getNo() {
return no;
}
public void setNo(String no) {
this.no = no;
}
public float getSal() {
return sal;
}
public void setSal(float sal) {
this.sal = sal;
}

}
class EnMan
{
  private ArrayList al=null;
 
  public void EnMan(){
  al=new ArrayList();  
 
 
 } 
  public void addE(Emg e1){

al.add(e1);
  }
  public void showInfo(String no){
for(int i=0;i<al.size();i++ )
{ Emg e2=(Emg)al.get(i);
if(e2.getNo().equals(no)){
System.out.println("该员工的信息是：");
System.out.println("该员工的编号是"+no);
System.out.println("该员工的工资是"+e2.getSal());