Create an ArrayList with multiple object types

Question

How do I create an ArrayList with integer and string input types  If I create one as   List lt Integer gt  sections   new ArrayList  lt Integer gt       that will be an Integer type ArrayList   If I create one as   List lt String gt  sections   new ArrayList  lt String gt       that will be of String type   How can I create an ArrayList which can take both integer and string input types  Thank you

User · Answer

You can just add objects of diffefent  Types  to an instance of ArrayList  No need create an ArrayList  Have a look at the below example   You will get below output    Beginning       Contents of array   String  1    Size of the list  2   This is not an Integer String   This is an Integer 1  package com viswa examples programs   import java util ArrayList  import java util Arrays   public class VarArrayListDemo         SuppressWarnings    rawtypes    unchecked         public static void main String   args            System out println   Beginning                 ArrayList varTypeArray   new ArrayList            varTypeArray add  String            varTypeArray add 1     Stored as Integer          System out println   Contents of array      varTypeArray     n Size of the list      varTypeArray size              Arrays stream varTypeArray toArray    forEach VarArrayListDemo  checkType              private static  lt T gt  void checkType T t             if  Integer class isInstance t                 System out println   This is an Integer     t             else               System out println   This is not an Integer    t

User · Answer

Just use Entry  as in java util Map Entry  as the list type  and populate it using  java util AbstractMap   s  SimpleImmutableEntry    List lt Entry lt Integer  String gt  gt  sections   new ArrayList lt  gt     sections add new SimpleImmutableEntry lt  gt  anInteger  orString

User · Answer

You can always create an ArrayList of Objects  But it will not be very useful to you   Suppose you have created the Arraylist like this   List lt Object gt  myList   new ArrayList lt Object gt      and add objects to this list like this   myList add new Integer  5      myList add  object     myList add new Object      You won t face any problem while adding and retrieving the object but it won t be very useful   You have to remember at what location each type of object is it in order to use it  In this case after retrieving  all you can do is calling the methods of Object on them

User · Answer

You can make it like    List lt Object gt  sections   new ArrayList  lt Object gt        Recommended  Another possible solution would be to make a custom model class with two parameters one Integer and other String  Then using an ArrayList of that object

User · Answer

List lt Object gt  list   new ArrayList lt  gt               list add 1             list add  1      As the return type of ArrayList is object  you can add any type of data to ArrayList but it is not a good practice to use ArrayList because there is unnecessary boxing and unboxing

User · Answer

1          ArrayList lt Object gt  list   new ArrayList  lt  gt              list add  ddd       list add 2      list add 11122 33          System out println list      2      ArrayList arraylist   new ArrayList     arraylist add 5            arraylist add  saman          arraylist add 4 3            System out println arraylist

User · Answer

You don t know the type is Integer or String then you no need Generic  Go With old style   List list  new ArrayList      list add 1   list add  myname     for Object o   list

User · Answer

You could create a List lt Object gt   but you really don t want to do this  Mixed lists that abstract to Object are not very useful and are a potential source of bugs  In fact the fact that your code requires such a construct gives your code a bad code smell and suggests that its design may be off  Consider redesigning your program so you aren t forced to collect oranges with orangutans    Instead -- do what G V recommends and I was about to recommend  create a custom class that holds both int and String and create an ArrayList of it  1  to his answer

User · Answer

It depends on the use case  Can you  please  describe it more   If you want to be able to add both at one time  than you can do the which is nicely described by  Sanket Parikh  Put Integer and String into a new class and use that   If you want to add the list either a String or an int  but only one of these at a time  then sure it is the List lt Object gt  which looks good but only for first sight  This is not a good pattern  You ll have to check what type of object you have each time you get an object from your list  Also This type of list can contain any other types as well   So no  not a nice solution  Although maybe for a beginner it can be used  If you choose this  i would recommend to check what is  quot instanceof quot  in Java   I would strongly advise to reconsider your needs and think about maybe your real nead is to encapsulate Integers to a List lt Integer gt  and Strings to a separate List lt String gt    Can i tell you a metaphor for what you want to do now  I would say you want to make a List wich can contain coffee beans and coffee shops  These to type of objects are totally different  Why are these put onto the same shelf     Or do you have maybe data which can be a word or a number  Yepp  This would make sense  both of them is data  Then try to use one object for that which contains the data as String and if needed  can be translated to integer value  public class MyDataObj   String info  boolean isNumeric   public MyDataObj String info       setInfo info      public MyDataObj Integer info       setInfo info      public String getInfo         return info     public void setInfo String info        this info   info      this isNumeric   false     public void setInfo Integer info        this info   Integer toString info       this isNumeric   true     public boolean isNumeric         return isNumeric       This way you can use List lt MyDataObj gt  for your needs  Again  this depends on your needs     Some edition  What about using inharitance  This is better then then List lt Object gt  solution  because you can not have other types in the list then Strings or Integers  Interface  public interface IMyDataObj   public String getInfo       For String  public class MyStringDataObj implements IMyDataObj    final String info   public MyStringDataObj String info       this info   info      Override public String getInfo         return info       For Integer  public class MyIntegerDataObj implements IMyDataObj    final Integer info   public MyIntegerDataObj Integer info        this info   info      Override public String getInfo         return Integer toString info        Finally the list will be  List lt IMyDataObj gt

User · Answer

I am also newish to Java and just figured this out  You should create your own class which stores the string and integer  and then make a list of these objects  For instance  I am sure this code is imperfect  but better than arrayList    class Stuff       private String label      private Integer value          Constructor or setter     public void Stuff String label  Integer value            if  label    null    value    null                return                    this label   label          this value   value                getters      public String getLabel             return this label             public Integer getValue             return this value            Then in your code   private ArrayList lt Stuff gt  items   new ArrayList lt Stuff gt     items add new Stuff label  value     for  Stuff item  items         doSomething item getLabel        returns String      doSomething item getValue        returns Integer

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User Defined Class Array List Example  import java util       public class UserDefinedClassInArrayList        public static void main String   args               Creating user defined class objects           Student s1 new Student 1  AAA  13             Student s2 new Student 2  BBB  14             Student s3 new Student 3  CCC  15             ArrayList lt Student gt  al new ArrayList lt Student gt             al add s1           al add s2             al add s3              Iterator itr al iterator                 traverse elements of ArrayList object           while itr hasNext                   Student st  Student itr next                  System out println st rollno     st name     st age                          class Student        int rollno        String name        int age        Student int rollno String name int age             this rollno rollno            this name name            this age age                 Program Output   1 AAA 13   2 BBB 14   3 CCC 15

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You can use Object for storing any type of value for e g  int  float  String  class objects  or any other java objects  since it is the root of all the class  For e g    Declaring a class  class Person   public int personId  public String personName   public int getPersonId         return personId     public void setPersonId int personId        this personId   personId     public String getPersonName         return personName     public void setPersonName String personName        this personName   personName      main function code  which creates the new person object  int  float  and string type  and then is added to the List  and iterated using for loop  Each object is identified  and then the value is printed        Person p   new Person    p setPersonId 1   p setPersonName  Tom     List lt Object gt  lstObject   new ArrayList lt Object gt     lstObject add 1232   lstObject add  String    lstObject add 122 212f   lstObject add p    for  Object obj   lstObject        if  obj getClass      String class            System out println  I found a string  -     obj             if  obj getClass      Integer class            System out println  I found an int  -     obj             if  obj getClass      Float class            System out println  I found a float  -     obj             if  obj getClass      Person class            Person person    Person  obj          System out println  I found a person object            System out println  Person Id  -     person getPersonId             System out println  Person Name  -     person getPersonName                You can find more information on the object class on this link Object in java

[java] Create an ArrayList with multiple object types?

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