Creating instance list of different objects

Question

I m tring to create an arraylist of different class instances  How can I create a list without defining a class type    lt Employee gt    List lt Employee gt  employees   new ArrayList lt Employee gt     employees add new Employee     Employee employee   employees get 0

User · Answer

List anyObject   new ArrayList     or  List lt Object gt  anyObject   new ArrayList lt Object gt      now anyObject can hold objects of any type   use instanceof to know what kind of object it is

User · Answer

How can I create a list without defining a class type    lt Employee gt     If I m reading this correctly  you just want to avoid having to specify the type  correct   In Java 7  you can do   List lt Employee gt  list   new ArrayList lt  gt       but any of the other alternatives being discussed are just going to sacrifice type safety

User · Answer

If you can t be more specific than Object with your instances  then use   List lt Object gt  employees   new ArrayList lt Object gt       Otherwise be as specific as you can   List lt   extends SpecificType gt  employees   new ArrayList lt   extends SpecificType gt

User · Answer

I see that all of the answers suggest using a list filled with Object classes and then explicitly casting the desired class  and I personally don t like that kind of approach   What works better for me is to create an interface which contains methods for retrieving or storing data from to certain classes I want to put in a list  Have those classes implement that new interface  add the methods from the interface into them and then you can fill the list with interface objects - List lt NewInterface gt  newInterfaceList   new ArrayList lt  gt    thus being able to extract the desired data from the objects in a list without having the need to explicitly cast anything    You can also put a comparator in the interface if you need to sort the list

User · Answer

You could create a list of Object like List lt Object gt  list   new ArrayList lt Object gt     As all classes implementation extends implicit or explicit from java lang Object class  this list can hold any object  including instances of Employee  Integer  String etc   When you retrieve an element from this list  you will be retrieving an Object and no longer an Employee  meaning you need to perform a explicit cast in this case as follows   List lt Object gt  list   new ArrayList lt Object gt     list add  String    list add Integer valueOf 1    list add new Employee      Object retrievedObject   list get 2   Employee employee    Employee list get 2      explicit cast

User · Answer

I believe your best shot is to declare the list as a list of objects   List lt Object gt  anything   new ArrayList lt Object gt       Then you can put whatever you want in it  like   anything add new Employee        Evidently  you will not be able to read anything out of the list without a proper casting   Employee mike    Employee  anything get 0     I would discourage the use of raw types like   List anything   new ArrayList     Since the whole purpose of generics is precisely to avoid them  in the future Java may no longer suport raw types  the raw types are considered legacy and once you use a raw type you are not allowed to use generics at all in a given reference  For instance  take a look a this another question  Combining Raw Types and Generic Methods

User · Answer

List lt Object gt  objects   new ArrayList lt Object gt       objects list will accept any of the Object  You could design like as follows  public class BaseEmployee    stuffs      public class RegularEmployee extends BaseEmployee    stuffs      public class Contractors extends BaseEmployee    stuffs       and in list  List lt   extends BaseEmployee gt  employeeList   new ArrayList lt   extends BaseEmployee gt

[java] Creating instance list of different objects

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