空指针异常

Question

package javajazzup;

public class LoginBean{
 String loginid;
 String pwd;

 public LoginBean(){}

 public String getLoginid(){
  return loginid;
 }
 public void setLoginid(String loginid){
  this.loginid = loginid;
 }
 public String getPwd(){
  return pwd;
 }
 public void setPwd(String pwd){
  this.pwd = pwd;
 }
 public String CheckValidUser(){
  if(loginid.equals("JavaJazzUp") && pwd.equals("mypwd")){
   return "success";
  }
  else{
   return "fail";
  }
 }
}

Answer 1

您应该将方法CheckValidUser()更改为：

    public String CheckValidUser(){
      if("JavaJazzUp".equals(loginid) && "mypwd".equals(pwd)){
         return "success";
      }else{
         return "fail";
      }
    }

Answer 2

测试用例

public static void LoginBeanTest() {
  LoginBean bean = new LoginBean();
  bean.setLoginid("JavaJazzUp");
  bean.setPwd("mypwd");
  System.out.println(bean.CheckValidUser());
  bean.setPwd("wrongpwd");
  System.out.println(bean.CheckValidUser());

  bean.setLoginid(null);
  try {
    System.out.println(bean.CheckValidUser());
  catch (NullPointerException npe) {
    System.out.println("NPE as expected");
  }

  bean.setLoginid("");
  bean.setPwd(null);
  try {
    System.out.println(bean.CheckValidUser());
  catch (NullPointerException npe) {
    System.out.println("NPE as expected");
  }
}

Answer 3

要获取null pointer，可以将loginid设置为null，或者将pwd设置为null。它们似乎没有正确设置。但如果不提供更多信息，我们无法帮助您。