How do I add a row to a 2D array?

Question

String loginInfo[][] = { { "mason", "dragon"   }, //First Column is usernames, second is passwords.
                         { "shay",  "stowers"  }, 
                         { "admin", "password" }, };

This is my array that has the username in the first col, passwords in the second col. I want to be able to add another row to this array once a user has submitted two strings.

Example...

String input1 = "username", String input2 = "password";

I want to take these two Strings and add them as a row, to the array. So my end result would look like this..

String loginInfo[][] = { { "mason",    "dragon"   },
                         { "shay",     "stowers"  },
                         { "admin",    "password" },
                         { "username", "password" }, };//This coming from input1 and input2

You can't... arrays are of fixed length. you'd better take a look at the java.util.Collections Framework. — Hungry Blue Dev
– Hungry Blue Dev, Commented Apr 5, 2014 at 4:57
Arrays are fixed-size, so you can't add to the original one. You need to make a new array that's at least one size bigger. A much better solution would be to use an List<List<String>>. — musical_coder
– musical_coder, Commented Apr 5, 2014 at 4:58

Keerthivasan · Accepted Answer · 2014-04-05 05:00:04Z

1

Perfect place to use an ArrayList of your user information JavaBean like

List<UserInfo> userInfo = new ArrayList<UserInfo>();

Whenever you receive userName and passWord, create an instance of UserInfo and add it to the list

UserInfo Class like below

class UserInfo{

 private String userName = null;

 private String passWord = null;

 // add a constructor
 public UserInfo(String userName, String passWord){
  this.userName = userName;
  this.passWord = passWord; 
 }

 //add setters and getters
 ...
 ...

}

Check it out. You will like it

Disclaimer : Not tested. Just a prototype!

answered Apr 5, 2014 at 5:00

Keerthivasan

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4 Comments

Hungry Blue Dev Over a year ago

Perhaps u could give a simple structure of the UserInfo class to the OP.

Hungry Blue Dev Over a year ago

Well done... too bad I can offer only one upvote. :-)

MasonAlt Over a year ago

Thanks, we haven't yet delved into multiple classes yet so I think I'll just stick to 2 lists for now, one for usernames and one for passwords.

Keerthivasan Over a year ago

No, Please create an object (Javabean) to store both username and password collectively and have a single list. This will keep your data organised.

user158017 · Accepted Answer · 2014-04-05 05:18:59Z

Arrays are not changeable. They are the length they are originally given. You have two options:

Create a new array, increasing its length, then copy the old array into the new one.
Use a collection in which Java has already done all this for you. Check out Lists.

EDIT: Example for option 1:

string[ ][ ] newloginInfo = new int[loginInfo.length * 2][2];

for (int i = 0; i < loginInfo.length; i++) {
    System.arraycopy(loginInfo[i], 0, newloginInfo[i], 0, loginInfo[0].length);
}

//now there is room for twice as many rows.  Add as usual.

Example for option 2: simply use the Generic list instead of the array to being with:

List<List<of string>> list = new ArrayList<List<of String>();

then you just call list.add to add in a new array:

List<of string> newrow = new ArrayList<of string>();
list.add(newrow);

apologies - not tested or thrown in an ide - check the syntax.

EDIT 2: Octopus's suggestion of having an object and then storing a list of those objects is really the way to go instead of dealing with multidimensional arrays - unless you have a REALLY good reason not you use it. It's cleaner, more organized, and your IDE will pick up the details in intellisense.

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