How to solve - java.lang.IncompatibleClassChangeError?

Question

I have two files, one is the front-end login.jsp and the back-end loginUser.java. I am trying to get the boolean from the loginUser.java. However, there come out a error java.lang.IncompatibleClassChangeError. I have no idea why this come out. How can I solve this error? Thanks.

Here is my code of 'login.jsp':

   try{
            out.println("HT");
                  login.LoginUser user = new login.LoginUser(id,pwd);
                  boolean login_success = user.isLogin(); <---This line have error.
                  //int role_id = user.get_role_id();                   
                  if (login_success){
                             out.println("Login Success");
                             // out.println(user.get_role_id().toString());

 %>
 <script>
    setTimeout(function () {
                window.location.href = "control_panel.jsp"; //will redirect to your blog page (an ex: blog.html)
        },2000);
 </script>
 <%
   }
    else{
       out.println("Login Failed");

 %>

Here is my code of 'loginUser.java':

public class LoginUser {

private String username,password;
public boolean login_success;
public int role_id;



public LoginUser(String username,String password){
    this.username=username;
    this.password=password;
    this.login_success=false;
    this.role_id = 0;
}

public boolean login(){
    db.DataConnect conn = new db.DataConnect();
    conn.connect();

    ResultSet login_result;
    String sql_statement = "SELECT COUNT(*) AS user_found, role_id FROM t_user WHERE user_name = '" + this.username + "' AND password = '" + this.password + "'";
    System.out.println(sql_statement);
    try{
        login_result = conn.select(sql_statement);
        if(login_result.next()){
            if(login_result.getInt("user_found") == 1){
                login_success = true;
                role_id = login_result.getInt("role_id");
            }
        }
    } catch (Exception e) {System.out.println(e);}
    conn.close();

    return login_success;
}

public boolean isLogin(){
    return true;
}


 }

However, the when I changed the line boolean login_success = user.isLogin(); to boolean login_success = user.login();, the error will not come out.

score 0 · Answer 1 · answered Nov 19 '16 at 08:55

As the errror clearly says that the class file is Incompatible, you can fix the issue by recompiling your source files and then add to the server classpath.

Thrown when an incompatible class change has occurred to some class definition. The definition of some class, on which the currently executing method depends, has since changed.

How to solve - java.lang.IncompatibleClassChangeError?

1 Answers1