How to create a Multidimensional ArrayList in Java

Question

I m fairly new to ArrayLists anyway but I need them for this project I m doing so if you guys could help me I would be more than grateful  Basically  I need to create a multidemensional ArrayList to hold String values  I know how to do this with a standard array   like so public static String     array        but this is no good because I don t know the size of my array  all I know is how many demensions it will have   So  if you guys know how to make a  dynamically resizable array with 2   demensions   please could you tell me   Thanks In advance  Andy  Edit Update    Maybe it would be easier to resize or define a standard array using a varible  But I don t know  It s probably easier to use my original idea of an ArrayList though    All I need is a complete example code to create a 2D ArrayList and add so example values to both dimensions without knowing the index

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You can have ArrayList with elements which would be ArrayLists itself

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Once I required 2-D arrayList and I created using List and ArrayList and the code is as follows   import java util     public class ArrayListMatrix        public static void main String args              List lt ArrayList lt Integer gt  gt  a   new ArrayList lt  gt              ArrayList lt Integer gt  a1   new ArrayList lt Integer gt             ArrayList lt Integer gt  a2   new ArrayList lt Integer gt             ArrayList lt Integer gt  a3   new ArrayList lt Integer gt               a1 add 1           a1 add 2           a1 add 3            a2 add 4           a2 add 5           a2 add 6            a3 add 7           a3 add 8           a3 add 9            a add a1           a add a2           a add a3             for ArrayList obj a                ArrayList lt Integer gt  temp   obj               for Integer job   temp                   System out print job                                 System out println                        Output   1 2 3   4 5 6   7 8 9   Source   https   www codepuran com java 2d-matrix-arraylist-collection-class-java

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If you re allowed to use predefined Java classes  you could do something like   private static ArrayList lt ArrayList lt String gt  gt  biDemArrList   new ArrayList lt ArrayList lt String gt  gt       Then you can add new elements  something like   ArrayList lt String gt  temp   new ArrayList lt String gt        added     temp add  Hello world     biDemArrList add temp     Hope you can understand what I mean and what s going on  Also  you ll need to import java util ArrayList  for this  if you re making use of the Java class

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ArrayList lt ArrayList lt String gt  gt  array   new ArrayList lt ArrayList lt String gt  gt      Depending on your requirements  you might use a Generic class like the one below to make access easier   import java util ArrayList   class TwoDimentionalArrayList lt T gt  extends ArrayList lt ArrayList lt T gt  gt        public void addToInnerArray int index  T element            while  index  gt   this size                  this add new ArrayList lt T gt                        this get index  add element              public void addToInnerArray int index  int index2  T element            while  index  gt   this size                  this add new ArrayList lt T gt                         ArrayList lt T gt  inner   this get index           while  index2  gt   inner size                  inner add null                      inner set index2  element

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ArrayList lt ArrayList lt String gt  gt     http   download oracle com javase 6 docs api java util ArrayList html  http   en wikipedia org wiki Generics in Java

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What would you think of this for 3D ArrayList - can be used similarly to arrays - see the comments in the code       import java util ArrayList      import java util List                  ArrayList3D simulates a 3 dimensional array  lt br gt         e g  myValue   arrayList3D get x  y  z  is the same as   lt br gt              myValue   array x  y  z   lt br gt         and lt br gt              arrayList3D set x  y  z  myValue  is the same as  lt br gt               array x  y  z    myValue   lt br gt         but keeps its full ArrayList functionality  thus its        benefits of ArrayLists over arrays  lt br gt          lt br gt          param  lt T gt  data type             public class ArrayList3D  lt T gt             private final List lt List lt List lt T gt  gt  gt  arrayList3D           public ArrayList3D                 arrayList3D   newArrayDim1                                                                                                               Get value of the given array element  lt br gt                                                 E g  get 2  5  3   lt br gt                                                 For 3 dim array this would equal to  lt br gt                                                      nyValue   array 2  5  3   lt br gt                                                  lt br gt                                                 Throws  IndexOutOfBoundsException                                                - if any index is out of range                                                    index  lt  0    index  gt   size    lt br gt                                                  lt br gt                                                  param dim1 index of the first dimension of the array list                                                 param dim2 index of the second dimension of the array list                                                 param dim3 index of the third dimension of the array list                                                 return value of the given array element  of type T                                                          public T get int dim1  int dim2  int dim3                List lt List lt T gt  gt        ar2   arrayList3D get dim1               List lt T gt              ar3   ar2 get dim2               return ar3 get dim3                                                                                                              Set value of the given array  lt br gt                                                 E g  set 2  5  3   my value    lt br gt                                                 For 3 dim array this would equal to  lt br gt                                                      array 2  5  3   my value   lt br gt                                                  lt br gt                                                 Throws  IndexOutOfBoundsException                                                - if any index is out of range                                                    index  lt  0    index  gt   size    lt br gt                                                  lt br gt                                                  param dim1 index of the first dimension of the array list                                                 param dim2 index of the second dimension of the array list                                                 param dim3 index of the third dimension of the array list                                                 param value value to assign to the given array                                                 lt br gt                                                          public void set int dim1  int dim2  int dim3  T value                arrayList3D get dim1  get dim2  set dim3  value                                                                                                             Set value of the given array element  lt br gt                                                 E g  set 2  5  3   my value    lt br gt                                                 For 3 dim array this would equal to  lt br gt                                                      array 2  5  3   my value   lt br gt                                                  lt br gt                                                 Throws  IndexOutOfBoundsException                                                - if any index is less then 0                                                   index  lt  0  lt br gt                                                  lt br gt                                                  param indexDim1 index of the first dimension of the array list                                                 param indexDim2 index of the second dimension of the array list                                                       If you set indexDim1 or indexDim2 to value higher                                                       then the current max index                                                        the method will add entries for the                                                       difference  The added lists will be empty                                                  param indexDim3 index of the third dimension of the array list                                                       If you set indexDim3 to value higher                                                       then the current max index                                                        the method will add entries for the                                                       difference and fill in the values                                                       of param   value                                                   param value value to assign to the given array index                                                          public void setOrAddValue int indexDim1                                     int indexDim2                                    int indexDim3                                     T value                 List lt T gt  ar3   setOrAddDim3 indexDim1  indexDim2                int max   ar3 size                 if  indexDim3  lt  0                  indexDim3   0              if  indexDim3  lt  max                  ar3 set indexDim3  value                for  int ix   max-1  ix  lt  indexDim3  ix                       ar3 add value                                      private List lt List lt List lt T gt  gt  gt  newArrayDim1                 List lt T gt  ar3   new ArrayList lt  gt                 List lt List lt T gt  gt  ar2   new ArrayList lt  gt                 List lt List lt List lt T gt  gt  gt  ar1   new ArrayList lt  gt                 ar2 add ar3               ar1 add ar2               return ar1                     private List lt List lt T gt  gt  newArrayDim2                 List lt T gt  ar3   new ArrayList lt  gt                 List lt List lt T gt  gt  ar2   new ArrayList lt  gt                 ar2 add ar3               return ar2                     private List lt T gt  newArrayDim3                 List lt T gt  ar3   new ArrayList lt  gt                 return ar3                      private List lt List lt T gt  gt  setOrAddDim2 int indexDim1                 List lt List lt T gt  gt  ar2   null               int max   arrayList3D size                if  indexDim1  lt  0                  indexDim1   0              if  indexDim1  lt  max                  return arrayList3D get indexDim1                for  int ix   max-1  ix  lt  indexDim1  ix                       ar2   newArrayDim2                    arrayList3D add ar2                             return ar2                      private List lt T gt  setOrAddDim3 int indexDim1  int indexDim2                 List lt List lt T gt  gt  ar2   setOrAddDim2 indexDim1               List lt T gt        ar3   null               int max   ar2 size                if  indexDim2  lt  0                  indexDim2   0              if  indexDim2  lt  max                  return ar2 get indexDim2                for  int ix   max-1  ix  lt  indexDim2  ix                       ar3   newArrayDim3                    ar2 add ar3                             return ar3                      public List lt List lt List lt T gt  gt  gt  getArrayList3D                 return arrayList3D                     And here is a test code           ArrayList3D lt Integer gt  ar   new ArrayList3D lt  gt              int max   3          for  int i1   0  i1  lt  max  i1                  for  int i2   0  i2  lt  max  i2                      for  int i3   0  i3  lt  max  i3                          ar setOrAddValue i1  i2  i3   i3   1     i2 max     i1 max max                        int x   ar get i1  i2  i3                       System out println   -     i1          i2          i3           x                                               Result output    0  0  0   1 0  0  1   2 0  0  2   3 0  1  0   4 0  1  1   5 0  1  2   6 0  2  0   7 0  2  1   8 0  2  2   9 1  0  0   10 1  0  1   11 1  0  2   12 1  1  0   13 1  1  1   14 1  1  2   15 1  2  0   16 1  2  1   17 1  2  2   18 2  0  0   19 2  0  1   20 2  0  2   21 2  1  0   22 2  1  1   23 2  1  2   24 2  2  0   25 2  2  1   26 2  2  2   27

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Credit goes for JAcob Tomao for the code  I only added some comments to help beginners like me understand it  I hope it helps      read about Generic Types In Java  amp  the use of class lt T     gt  syntax    This class will Allow me to create 2D Arrays that do not have fixed sizes     class TwoDimArrayList lt T gt  extends ArrayList lt ArrayList lt T gt  gt        public void addToInnerArray int index  T element            while  index  gt   this size                     Create enough Arrays to get to position   index             this add new ArrayList lt T gt          as if going along Vertical axis                       this get index  returns the Arraylist instance at the  index  position         this get index  add element       as if going along Horizontal axis             public void addToInnerArray int index  int index2  T element            while  index  gt   this size                  this add new ArrayList lt T gt         as if going along Vertical                     access the inner ArrayList at the  index  position          ArrayList lt T gt  inner   this get index           while  index2  gt   inner size                    add enough positions containing  null  to get to the position index 2                     within the inner array   if the requested position is too far              inner add null       as if going along Horizontal axis                      Overwrite  null  or  old element  with the new  element  at the  index 2                  position of the chosen index  inner ArrayList         inner set index2  element       as if going along Horizontal axis

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Here an answer for those who d like to have preinitialized lists of lists  Needs Java 8    import java util ArrayList  import java util List  import java util stream Collectors  import java util stream IntStream   class Scratch      public static void main String   args        int M   4      int N   3          preinitialized array     list of lists  of strings  sizes not fixed     List lt List lt String gt  gt  listOfListsOfString   initializeListOfListsOfT M  N   -        System out println listOfListsOfString           preinitialized array     list of lists  of int  primitive type   sizes not fixed     List lt List lt Integer gt  gt  listOfListsOfInt   initializeListOfListsOfInt M  N  7       System out println listOfListsOfInt          public static  lt T gt  List lt List lt T gt  gt  initializeListOfListsOfT int m  int n  T initValue        return IntStream          range 0  m           boxed            map i - gt  new ArrayList lt T gt  IntStream              range 0  n               boxed                map j - gt  initValue               collect Collectors toList                        collect Collectors toList            public static List lt List lt Integer gt  gt  initializeListOfListsOfInt int m  int n  int initValue        return IntStream          range 0  m           boxed            map i - gt  new ArrayList lt  gt  IntStream              range 0  n               map j - gt  initValue               boxed                collect Collectors toList                        collect Collectors toList             Output     -  -  -    -  -  -    -  -  -    -  -  -     7  7  7    7  7  7    7  7  7    7  7  7     Side note for those wondering about IntStream   IntStream      range 0  m       boxed     is equivalent to   Stream      iterate 0  j - gt  j   1       limit n

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Wouldn t List lt ArrayList lt String gt  gt  2dlist   new ArrayList lt ArrayList lt String gt  gt     be a better  more efficient  implementation

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You can also do something like this         First create and Initialize the matrix or multidimensional arraylist  ArrayList lt ArrayList lt Integer gt  gt  list     MultidimentionalArrayList int x int y              list   new ArrayList lt  gt           for int i 0 i lt  x i                    ArrayList lt Integer gt  temp   new ArrayList lt  gt  Collections nCopies y 1 0            list add temp                  Add element at specific position   void add int row int column int val     list get row  set column val      list row  column  val         This static matrix can be change into dynamic if check that row and   column are out of bound  just  insert extra temp arraylist for row    remove element   int remove int row  int column             return list get row  remove column     del list row  column

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I can think of An Array inside an Array or a Guava s MultiMap   e g   ArrayList lt ArrayList lt String gt  gt  matrix   new ArrayList lt ArrayList lt String gt  gt

[java] How to create a Multidimensional ArrayList in Java?

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