Add: finUser method to GuestUser class, implemented in User class

src/model/users/GuestUser.java

 package model.users;
 
-public class GuestUser {
+import model.users.User;
+
+public abstract class GuestUser {
 
 	private int generatedId;
 	private static int IdCounter = 0;
 	
+	
 	//CONSTRUCTOR
 	public GuestUser() {
 		generatedId = ++IdCounter;
@@ -17,5 +20,6 @@ public class GuestUser {
 		return generatedId;
 	}
 	//OTHER METHODS
+	public abstract User findUser(int id);
 	
 }

src/model/users/PrivateUser.java

@@ -70,6 +70,9 @@ public class PrivateUser extends User{
 		posts.add(newPost);
 		return newPost;
 	}
+
+
+	
 	
 	
 }

src/model/users/User.java

@@ -15,6 +15,7 @@ public abstract class User extends GuestUser implements IPost{
 	private String password;
 	private String generatedPassword;
 	//MD5 hashes are no longer considered cryptographically secure, and they should not be used for cryptographic authentication.
+	public static ArrayList<User> allUsers = new ArrayList<User>();
 	
 	//CONSTRUCTORS
 	public User() {
@@ -23,6 +24,7 @@ public abstract class User extends GuestUser implements IPost{
 		username = "Empty";
 		password = "Empty";
 		generatedPassword = null;
+		allUsers.add(this);
 	}
 	
 	public User(String nameAndSurname, String username, String password) {
@@ -38,6 +40,7 @@ public abstract class User extends GuestUser implements IPost{
 			this.password = "Empty";
 			generatedPassword = null;
 		}
+		allUsers.add(this);
 			 
 	}
 	
@@ -63,6 +66,10 @@ public abstract class User extends GuestUser implements IPost{
 		
 	}
 
+	public void setAllUsers(ArrayList<User> userList) {
+		allUsers = (userList != null) ? userList : new ArrayList<User>();
+	}
+	
 	
 	//GETTERS
 	public String getNameAndSurname() {
@@ -81,6 +88,10 @@ public abstract class User extends GuestUser implements IPost{
 		return generatedPassword;
 	}
 	
+	public ArrayList<User> getAllUsers() {
+		return allUsers;
+	}
+	
 	//OTHER METHODS
 	public String toString() {
 		return  "User ID: " + super.getId() + "Full name: " + nameAndSurname + ", Username: " + username;
@@ -101,9 +112,13 @@ public abstract class User extends GuestUser implements IPost{
 		return false;
 	}
 	
-	//IMPLEMENTED METHODS
-	//public void createPost(PostType postType, String msg) {}
-	//don't implement this if derived classes has to have implementation
-	//}
+	//DERRIVED METHODS
+	@Override
+	public User findUser(int id) {
+		for(User usr: allUsers) {
+			if(usr.getId() == id) return usr;
+		}
+		return null;
+	}
 	
 }