How can I dynamically add items to a Java array

Question

In PHP  you can dynamically add elements to arrays by the following    x   new Array     x     1   x     2    After this   x would be an array like this   1 2    Is there a way to do something similar in Java

User · Answer

I have seen this question very often in the web and in my opinion, many people with high reputation did not answer these questions properly. So I would like to express my own answer here.

First we should consider there is a difference between array and arraylist.

The question asks for adding an element to an array, and not ArrayList

The answer is quite simple. It can be done in 3 steps.

Convert array to an arraylist
Add element to the arrayList
Convert back the new arrayList to the array

Here is the simple picture of it

And finally here is the code:

Step 1:

public List<String> convertArrayToList(String[] array){
        List<String> stringList = new ArrayList<String>(Arrays.asList(array));
        return stringList;
    }

Step 2:

public  List<String> addToList(String element,List<String> list){

            list.add(element);
            return list;
    }

Step 3:

public String[] convertListToArray(List<String> list){
           String[] ins = (String[])list.toArray(new String[list.size()]);
           return ins;
    }

Step 4

public String[] addNewItemToArray(String element,String [] array){
        List<String> list = convertArrayToList(array);
        list= addToList(element,list);
        return  convertListToArray(list);
}

User · Answer

In Java size of array is fixed   but you can add elements dynamically to a fixed sized array using its index and for loop  Please find example below   package simplejava   import java util Arrays              author sashant     public class SimpleJava                    param args the command line arguments             public static void main String   args               TODO code application logic here          try              String   transactions              transactions   new String 10                for int i   0  i  lt  transactions length  i                     transactions i     transaction -   Integer toString i                                          System out println Arrays toString transactions              catch Exception exc               System out println exc getMessage                 System out println Arrays toString exc getStackTrace

User · Answer

Look at java util LinkedList or java util ArrayList  List lt Integer gt  x   new ArrayList lt Integer gt     x add 1   x add 2

User · Answer

keep a count of where you are in the primitive array  class recordStuff extends Thread       double   aListOfDoubles      int i   0       void run                 double newData          newData   getNewData       gets data from somewhere          aListofDoubles i    newData     adds it to the primitive array of doubles         i      increments the counter for the next pass          System out println  mode      doStuff                void doStuff                    Calculate the mode of the double   array          for  int i   0  i  lt  aListOfDoubles length  i                           int count   0              for  int j   0  j  lt  aListOfDoubles length  j                                  if  a j     a i   count                              if  count  gt  maxCount                                 maxCount   count                  maxValue   aListOfDoubles i                                   return maxValue

User · Answer

Arrays in Java have a fixed size  so you can t  add something at the end  as you could do in PHP   A bit similar to the PHP behaviour is this   int   addElement int   org  int added        int   result   Arrays copyOf org  org length  1       result org length    added      return result      Then you can write   x   new int 0   x   addElement x  1   x   addElement x  2    System out println Arrays toString x      But this scheme is horribly inefficient for larger arrays  as it makes a copy of the whole array each time   And it is in fact not completely equivalent to PHP  since your old arrays stays the same    The PHP arrays are in fact quite the same as a Java HashMap with an added  max key   so it would know which key to use next  and a strange iteration order  and a strange equivalence relation between Integer keys and some Strings   But for simple indexed collections  better use a List in Java  like the other answerers proposed   If you want to avoid using List because of the overhead of wrapping every int in an Integer  consider using reimplementations of collections for primitive types  which use arrays internally  but will not do a copy on every change  only when the internal array is full  just like ArrayList    One quickly googled example is this IntList class    Guava contains methods creating such wrappers in Ints asList  Longs asList  etc

User · Answer

You can dynamically add elements to an array using Collection Frameworks in JAVA  collection Framework doesn t work on primitive data types   This Collection framework will be available in  java util    package  For example if you use ArrayList    Create an object to it and then add number of elements  any type like String  Integer    etc   ArrayList a   new ArrayList    a add  suman    a add new Integer 3    a add  gurram      Now you were added 3 elements to an array   if you want to remove any of added elements  a remove  suman      again if you want to add any element  a add  Gurram      So the array size is incresing   decreasing dynamically

User · Answer

This is a simple way to add to an array in java  I used a second array to store my original array  and then added one more element to it  After that I passed that array back to the original one       int    test    12 22 33       int    test2  new int test length 1       int m 5 int mz 0      for   int test3  test                              test2 mz  test3  mz                       test2 mz    m      test test2       for   int test3  test               System out println test3

User · Answer

Apache Commons has an ArrayUtils implementation to add an element at the end of the new array       Copies the given array and adds the given element at the end of the new array     public static  lt T gt  T   add T   array  T element

User · Answer

You probably want to use an ArrayList for this -- for a dynamically sized array like structure

User · Answer

You can use an ArrayList and then use the toArray   method  But depending on what you are doing  you might not even need an array at all  Look into seeing if Lists are more what you want   See  Java List Tutorial

User · Answer

Use an ArrayList or juggle to arrays to auto increment the array size

[java] How can I dynamically add items to a Java array?

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