ArrayList - How to modify a member of an object

Question

I have a number of Customer objects stored in an ArrayList  My Customer class has 2 data members  Name and Email  Now I want to modify just the Email for Customer  Doe    Now if  Doe  is located at index 3 in the list  I know I can write this line   myList set  3  new Customer   Doe    j doe supermail com         But that means creating a new object  If I have a very big list  I suppose the process would be very slow  Is there any other way to directly access the data member of an Object stored in an ArrayList  maybe by using another kind of Collection than ArrayList

User · Answer

You can do this   myList get 3  setEmail  new email

User · Answer

If you need fast lookup  basically constant time  of a object stored in your collection you should use Map instead of List   If you need fast iteration of the objects you should use List   So in your case     Map lt String Customer gt  customers   new HashMap lt String Customer gt        somewhere in the code you fill up the Map  assuming customer names are unique customers put customer getName    customer      at some later point you retrieve it like this      this is fast  given a good hash    been calculated for the  keys  in your map  in this case the keys are unique     String objects so the default hash algorithm should be fine Customer theCustomerYouLookFor   customers get  Doe        modify it theCustomerYouLookFor setEmail  newEmail stackoverflow com

User · Answer

Use myList get 3  to get access to the current object and modify it  assuming instances of Customer have a way to be modified

User · Answer

I wrote you 2 classes to show you how it s done  Main and Customer  If you run the Main class you see what s going on   import java util     public class Customer        private String name      private String email       public Customer String name  String email            this name   name          this email   email             public String getName             return name             public void setName String name            this name   name             public String getEmail             return email             public void setEmail String email            this email   email              Override     public String toString             return name           email             public static String toString Collection lt Customer gt  customers            String s               for Customer customer   customers                s    customer     n                     return s             import java util     public class Main        public static void main String   args            List lt Customer gt  customers   new ArrayList lt  gt             customers add new Customer  Bert    bert gmail com             customers add new Customer  Ernie    ernie gmail com             System out println  customers before email change - start            System out println Customer toString customers            System out println  end            customers get 1  setEmail  new email gmail com            System out println  customers after email change - start            System out println Customer toString customers            System out println  end               to get this running  make 2 classes  Main and Customer and copy paste the contents from both classes to the correct class  then run the Main class

User · Answer

Any method you use  there will always be a loop like in removeAll   and set     So  I solved my problem like this   for  int i   0  i  lt  myList size    i               if  myList get i  getName   equals varName                  myList get i  setEmail varEmail               break                     Where varName    Doe  and varEmail    j doe supermail com    I hope this help you

User · Answer

Try this This works while traversing the code and modifying the fields at once of all the elements of Arraylist   public Employee String name String email   this name name  this email email     public void setName String name    this name   name     public String getName     return name     public void setEmail String email    this email   email     public String getEmail     return email     for int i 0 i     List get i  setName  Anonymous    List get i  setEmail  xyz abc com

User · Answer

You can just do a get on the collection then just modify the attributes of the customer you just did a  get  on   There is no need to modify the collection nor is there a need to create a new customer   int currentCustomer   3      get the customer at 3 Customer c   list get currentCustomer      change his email c setEmail  somethingelse example com

User · Answer

Well u have used Pojo Entity so u can do this  u need to get object of that and have to set data   myList get 3  setEmail  email      that way u can do that  or u can set other param too

User · Answer

Assuming Customer has a setter for email - myList get 3  setEmail  j doe supermail com

User · Answer

Fixed  I was wrong  this only applies on element reassignment  I thought that the returned object wasn t referencing the new one   It can be done   Q  Why  A  The get   method returns an object referencing  the original one   So  if you write myArrayList get 15  itsVariable   7or myArrayList get 15  myMethod  My Value   you are actually assigning a value   using a method from the object referenced by the returned one  this means  the change is applied to the original object   The only thing you can t do is myArrayList get 15    myNewElement  To do this you have to use list set   method

User · Answer

You can iterate through arraylist to identify the index and eventually the object which you need to modify  You can use for-each for the same as below   for Customer customer   myList        if customer  null  amp  amp   Doe  equals customer getName               customer setEmail  abc xyz com            break            Here customer is a reference to the object present in Arraylist  If you change any property of this customer reference  these changes will reflect in your object stored in Arraylist

User · Answer

Without function here it is   it works fine with listArrays filled with Objects  example         al add new Student 101  Jack  23  C      adding Student class object         al add new Student 102  Evan  21  A             al add new Student 103  Berton  25  B             al add 0  new Student 104  Brian  20  D           al add 0  new Student 105  Lance  24  D           for int i   101  i lt  101 al size    i                      al get i-101  rollno   i   rollno is 101  102   103

[java] ArrayList - How to modify a member of an object?

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