Java how do I initialize an array size if it s unknown

Question

I m asking the user to enter some numbers between 1 and 100 and assign them into an array  The array size is not initialized since it is dependent on the number of times the user enters a number  How should I assign the array length  If user enters 5 6 7 8 9  5 numbers   then int   list     becomes int   list   new int 5    I m trying to use a loop  but it won t stop  int   integers  int j   0  do          integers   new int j   1          integers j    in nextInt            j            while  integers j-1   gt   1     integers j-1    lt   100

User · Answer

int i largest   0  Scanner scan   new Scanner System in   System out println  Enter the number of numbers in the list    i   scan nextInt    int arr     new int i   System out println  Enter the list of numbers     for int j 0 j lt i j         arr j    scan nextInt        The above code works well  I have taken the input of the number of elements in the list and initialized the array accordingly

User · Answer

String line sc nextLine        int counter 1      for int i 0 i lt line length   i              if line charAt i                      counter                        long   numbers new long counter       counter 0      for int i 0 i lt line length   i             int j i          while true                if j gt  line length      line charAt j                          break                            j                      numbers counter  Integer parseInt line substring i j            i j          counter                for int i 0 i lt counter i              System out println numbers i                I always use this code for situations like this  beside you can recognize two or three or more digit numbers

User · Answer

You should use a List for something like this  not an array  As a general rule of thumb  when you don t know how many elements you will add to an array before hand  use a List instead  Most would probably tackle this problem by using an ArrayList   If you really can t use a List  then you ll probably have to use an array of some initial size  maybe 10   and keep track of your array capacity versus how many elements you re adding  and copy the elements to a new  larger array if you run out of room  this is essentially what ArrayList does internally   Also note that  in the real world  you would never do it this way - you would use one of the standard classes that are made specifically for cases like this  such as ArrayList

User · Answer

I think you need use List or classes based on that   For instance   ArrayList lt Integer gt  integers   new ArrayList lt Integer gt     int j   do      integers add int nextInt         j     while   integers get j-1   gt   1      integers get j-1   lt   100       You could read this article for getting more information about how to use that

User · Answer

input of list of number for array from single line      String input   sc nextLine        String arr     input split           int new arr     new int arr length       for int i 0  i lt arr length  i                   new arr i    Integer parseInt arr i

User · Answer

I agree that a data structure like a List is the best way to go   List lt Integer gt  values   new ArrayList lt Integer gt     Scanner in   new Scanner System in   int value  int numValues   0  do       value   in nextInt        values add value     while  value  gt   1   amp  amp   value  lt   100     Or you can just allocate an array of a max size and load values into it   int maxValues   100  int    values   new int maxValues   Scanner in   new Scanner System in   int value  int numValues   0  do       value   in nextInt        values numValues      value    while  value  gt   1   amp  amp   value  lt   100   amp  amp   numValues  lt  maxValues

User · Answer

If you want to stick to an array then this way you can make use  But its not good as compared to List and not recommended  However it will solve your problem   import java util Scanner   public class ArrayModify        public static void main String   args            int   list          String st          String   stNew          Scanner scan   new Scanner System in           System out println  Enter Numbers         If user enters 5 6 7 8 9          st   scan nextLine            stNew   st split    s             list   new int stNew length      Sets array size to 5          for  int i   0  i  lt  stNew length  i                 list i     Integer parseInt stNew i                System out println  You Enterred      list i

[java] Java: how do I initialize an array size if it's unknown?

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