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

<强>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

要获得null pointer loginid，null或pwd为null。似乎他们没有正确设置。但是，如果没有提供更多信息，我们无法帮助您。

Answer 4

您的私有成员变量loginid和pwd都在默认构造函数中初始化为null，因为您没有做任何事情来将它们设置为任何默认值。如果您取消引用任何一个而不将它们设置为非空引用，您将获得NullPointerException。

试试这样：

package javajazzup; 

public class LoginBean{ 
 String loginid; 
 String pwd; 

 public LoginBean(String user, String password)
 {
    this.loginid = user;
    this.pwd = password;
 }

 public LoginBean()
 {
    this("", "");
 } 

 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 boolean checkValidUser(String username, String password)
 { 
     return (loginid.equals(username) && pwd.equals(password)); 
 }

}

空指针异常

4 个答案: