Questions about casting

Question

I am trying to make a game with auth system in Java. When I am trying to run it, i can see an exception thrown in the console log but there is no error in the project. I know this is runtime error

The console log displays the following information:

Exception in thread "main" java.lang.ClassCastException: com.google.gson.internal.LinkedTreeMap cannot be cast to Auth$Profile
    at Auth.<init>(Auth.java:30)

Here is my code:

 public Auth(File profilesFile) {
              try {
                  ProfilesJSON e = (ProfilesJSON)this.gson.fromJson(new FileReader(profilesFile), ProfilesJSON.class);
                 Map ps = e.authenticationDatabase;
                 Iterator var5 = ps.keySet().iterator();

                 while(var5.hasNext()) {
                    String name = (String)var5.next();
                    Profile p = (Profile)ps.get(name);
                    if(p != null) {
                       if(p.displayName == null || p.displayName.length() == 0) {
                          p.displayName = p.username;
                       }

                       this.profiles.add(p);
                    }
                 }

              } catch (FileNotFoundException var7) {
                 ;
              } catch (NullPointerException var8) {
                 ;
              }
           }


    public class Profile {

              public String username;
              public String password;
              public String uid;
              public String displayName;
              public String name;
              public String playerUID;


              public Profile(String u, String t, String id, String d) {
                 this.username = u;
                 this.password = t;
                 this.uid = id;
                 this.displayName = d;
              }
           }

public class ProfilesJSON {

          public Map profiles;
          public String selectedProfile;
          public String password;
          public Map authenticationDatabase;


       }

Line 30 is:

Profile p = (Profile)ps.get(name);

This is a part of my code, my idea is if the player press "Remember Password", the game will generate a .json file to store his infomation..I just want to know what I did wrong, other code i can write it myself

Answer 1

Your ps.get(name) is returning a com.google.gson.internal.LinkedTreeMap object instead of Profile .

try to change it to:

LinkedTreeMap p = (LinkedTreeMap )ps.get(name);

Your code doesn't show you errors because there's no error in compile time, ClassCastException is a runtime exception.