Java - remove last known item from ArrayList

Question

OK  so here is my ArrayList   private List lt ClientThread gt  clients   new ArrayList lt ClientThread gt       and here is what I am trying to do  I am trying to remove the last known item from the ArrayList I posted above  I m trying to do this with the code below         catch SocketException re                                  String hey   clients get clients size                                 ClientThread remove hey                               System out println hey     has logged out                                 System out println  CONNECTED PLAYERS      clients size         but I am getting this error   C  wamp www mystikrpg Server java 147  incompatible types found     Server ClientThread required  java lang String                         String hey   clients get clients size                                                       C  wamp www mystikrpg Server java 148  cannot find symbol symbol    method remove java lang String  location  class Server ClientThread                         ClientThread remove hey                                         2 errors   What am I doing wrong  It s supposed to remove the last known item from my ArrayList

User · Answer

You re trying to assign the return value of clients get clients size    to the string hey  but the object returned is a ClientThread  not a string  As Andre mentioned  you need to use the proper index as well   As far as your second error is concerned  there is no static method remove   on the type ClientThread  Really  you likely wanted the remove method of your List instance  clients   You can remove the last item from the list  if there is one  as follows  Since remove also returns the object that was removed  you can capture the return and use it to print out the name   int size   clients size     if  size  gt  0        ClientThread client   clients remove size - 1        System out println client     has logged out         System out println  CONNECTED PLAYERS      clients size

User · Answer

You need to understand java generics  You have a list of ClientThread but trying to get String  You have other errors  but this one is very basic

User · Answer

First error  You re casting a ClientThread as a String for some reason   Second error  You re not calling remove on your List   Is is homework  If so  you might want to use the tag

User · Answer

It should be   ClientThread hey   clients get clients size   - 1   clients remove hey     Or you can do  clients remove clients size   - 1     The minus ones are because size   returns the number of elements  but the ArrayList s first element s index is 0 and not 1

User · Answer

clients get will return a ClientThread and not a String  and it will bomb with an IndexOutOfBoundsException if it would compile as Java is zero based for indexing   Similarly I think you should call remove on the clients list   ClientThread hey   clients get clients size  -1   clients remove hey   System out println hey     has logged out     System out println  CONNECTED PLAYERS      clients size       I would use the stack functions of a LinkedList in this case though    ClientThread hey   clients removeLast

User · Answer

The compiler complains that you are trying something of a list of ClientThread objects to a String  Either change the type of hey to ClientThread or clients to List lt String gt    In addition  Valid indices for lists are from 0 to size  -1   So you probably want to write     String hey   clients get clients size  -1

User · Answer

This line means you instantiated a  List of ClientThread Objects    private List lt ClientThread gt  clients   new ArrayList lt ClientThread gt       This line has two problems   String hey   clients get clients size       1  This part of the line    clients get clients size       ALWAYS throws IndexOutOfBoundsException because a collections size is always one bigger than its last elements index   2  Compiler complains about incompatible types because you cant assign a ClientThread object to String object  Correct one should be like this   ClientThread hey   clients get clients size  -1     Last but not least  If you know index of the object to remove just write   clients remove 23     Lets say it is in 23  index   Don t write     ClientThread hey   clients get 23        clients remove hey     because you are forcing the list to search for the index that you already know  If you plan to do something with the removed object later  Write     ClientThread hey   clients remove 23      This way you can remove the object and get a reference to it at the same line    Bonus  Never ever call your instance variable with name  hey   Find something meaningful   And Here is your corrected and ready-to-run code   public class ListExampleForDan        private List lt ClientThread gt  clients   new ArrayList lt ClientThread gt          public static void main String args               clients add new ClientThread  First and Last Client Thread              boolean success   removeLastElement clients            if  success                 System out println  Last Element Removed                else                System out println  List Is Null Empty  Operation Failed                            public static boolean removeLastElement List clients             if  clients    null    clients isEmpty                   return false             else                clients remove clients size   - 1                return true                        Enjoy

[java] Java - remove last known item from ArrayList

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