Arrays fill with multidimensional array in Java

Question

How can I fill a multidimensional array in Java without using a loop  I ve tried   double     arr   new double 20  4   Arrays fill arr  0     This results in java lang ArrayStoreException  java lang Double

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public static Object   fillArray Object   arr Object item       Arrays fill arr  item       return arr    Character     maze   new Character 10  10       fillArray maze  fillArray maze 0               for int i   0 i lt 10 i             System out println            for int j   0 j lt 10 j                 System out print maze i  j                      i hope this do well

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how can I fill a multidimensional array in Java without using a loop    Multidimensional arrays are just arrays of arrays and fill      doesn t check the type of the array and the value you pass in  this responsibility is upon the developer     Thus you can t fill a multidimensional array reasonably well without using a loop   Be aware of the fact that  unlike languages like C or C    Java arrays are objects and in multidimensional arrays all but the last level contain references to other Array objects  I m not 100  sure about this  but most likely they are distributed in memory  thus you can t just fill a contiguous block without a loop  like C C   would allow you to do

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double     arr   new double 20  4   Arrays fill arr 0   0   Arrays fill arr 1   0   Arrays fill arr 2   0   Arrays fill arr 3   0   Arrays fill arr 4   0   Arrays fill arr 5   0   Arrays fill arr 6   0   Arrays fill arr 7   0   Arrays fill arr 8   0   Arrays fill arr 9   0   Arrays fill arr 10   0   Arrays fill arr 11   0   Arrays fill arr 12   0   Arrays fill arr 13   0   Arrays fill arr 14   0   Arrays fill arr 15   0   Arrays fill arr 16   0   Arrays fill arr 17   0   Arrays fill arr 18   0   Arrays fill arr 19   0

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Arrays fill works only with one-dimensional array  Source of java util Arrays   public static void fill Object   a  Object val            int i   0           for int len   a length  i  lt  len    i                a i    val              Use own loops for initialization array

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This is because a double     is an array of double   which you can t assign 0 0 to  it would be like doing double   vector   0 0   In fact  Java has no true multidimensional arrays   As it happens  0 0 is the default value for doubles in Java  thus the matrix will actually already be filled with zeros when you get it from new  However  if you wanted to fill it with  say  1 0 you could do the following   I don t believe the API provides a method to solve this without using a loop  It s simple enough however to do it with a for-each loop   double     matrix   new double 20  4       Fill each row with 1 0 for  double   row  matrix      Arrays fill row  1 0

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As Per Java 8  we can use this way    double     arr   new double 20  4   Arrays stream arr  forEach a - gt  Arrays fill a  0     We can initialize a value in multidimensional array in a nicer and smart way

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The OP asked how to solve this problem without a loop   For some reason it is fashionable these days to avoid loops   Why is this   Probably there is a realization that using map  reduce  filter  and friends  and methods like each hide loops and cut down on program verbage and are kind of cool   The same goes for really sweet Unix pipelines   Or jQuery code   Things just look great without loops   But does Java have a map method   Not really  but we could define one with a Function interface with an eval or exec method   It isn t too hard and would be a good exercise   It might be expensive and not used in practice   Another way to do this without a loop is to use tail recursion   Yes  it is kind of silly and no one would use it in practice either  but it does show  maybe  that loops are fine in this case   Nevertheless  just to show  yet another loop free example  and to have fun  here is   import java util Arrays  public class FillExample       private static void fillRowsWithZeros double     a  int rows  int cols            if  rows  gt   0                double   row   new double cols               Arrays fill row  0 0               a rows    row              fillRowsWithZeros a  rows - 1  cols                        public static void main String   args            double     arr   new double 20  4           fillRowsWithZeros arr  arr length - 1  arr 0  length           System out println Arrays deepToString arr              It isn t pretty  but in answer to the OP s question  there are no explicit loops

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Arrays fill works with single dimensional array  so to fill two dimensional array we can do below  for  int i   0  len   arr length  i  lt  len  i        Arrays fill arr i   0

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Don t we all sometimes wish there was a  lt T gt void java util Arrays deepFill T     multiDimensional   Problems start with Object threeByThree       new Object 3  3   threeByThree 1    null  and threeByThree 2  1    new int   42   being perfectly legal   If only Object twoDim  final   was legal and well defined      Using one of the public methods from below keeps loops from the calling source code  If you insist on using no loops at all  substitute the loops and the call to Arrays fill      using recursion        Fills matrix   code m  with   code value       return   code m  s dimensionality      throws java lang ArrayStoreException if the component type     of a subarray of non-zero length at the bottom level     doesn t agree with   code value  s type     public static  lt T gt int deepFill Object   m  T value        Class lt   gt  components       if  null    m            null     components   m getClass   getComponentType             return 0      int dim   0      do         dim        while  null     components   components getComponentType          filler  Object     m  value  dim       return dim        Fills matrix   code m  with   code value       throws java lang ArrayStoreException if the component type     of a subarray of non-zero length at level   code dimensions      doesn t agree with   code value  s type     public static  lt T gt void fill Object   m  T value  int dimensions        if  null    m          filler m  value  dimensions      static  lt T gt void filler Object   m  T value  int toGo        if  --toGo  lt   0          java util Arrays fill m  value       else         for  Object   subArray    Object     m              if  null    subArray                  filler subArray  value  toGo

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Arrays fill arr  new double 4

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In simple words java donot provide such an API  You need to iterate through loop and using fill method you can fill 2D array with one loop         int row   5        int col   6        int cache     new int row  col         for int i 0 i lt  row i               Arrays fill cache i

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Using Java 8  you can declare and initialize a two-dimensional array without using a  explicit  loop as follows   int x   20     first dimension int y   4     second dimension  double     a   IntStream range 0  x                           mapToObj i - gt  new double y                            toArray i - gt  new double x        This will initialize the arrays with default values  0 0 in the case of double    In case you want to explicitly define the fill value to be used  You can add in a DoubleStream   int x   20     first dimension int y   4     second dimension double v   5 0     fill value  double     a   IntStream          range 0  x           mapToObj i - gt  DoubleStream generate    - gt  v  limit y  toArray             toArray i - gt  new double x

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As an extension to the answer  I found this post but was looking to fill a 4 dimensional array  The original example is only a two dimensional array  but the question says  multidimensional   I didn t want to post a new question for this     You can use the same method  but you have to nest them so that you eventually get to a single dimensional array   fourDArray   new float 10  10  10  1      Fill each row with null for  float       row  fourDArray        for  float     innerRow  row                for  float   innerInnerRow  innerRow                    Arrays fill innerInnerRow  -1000

[java] Arrays.fill with multidimensional array in Java

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