Getting the array length of a 2D array in Java

Question

I need to get the length of a 2D array for both the row and column   I   ve successfully done this  using the following code   public class MyClass     public static void main String args            int     test     test   new int 5  10      int row   test length    int col   test 0  length     System out println row     System out println col             This prints out 5  10 as expected   Now take a look at this line     int col   test 0  length    Notice that I actually have to reference a particular row  in order to get the column length   To me  this seems incredibly ugly   Additionally  if the array was defined as   test   new int 0  10     Then the code would fail when trying to get the length   Is there a different  more intelligent  way to do this

User · Answer

A 2D array is not a rectangular grid  Or maybe better  there is no such thing as a 2D array in Java    import java util Arrays   public class Main     public static void main String args           int     test       test   new int 5       2D array      for  int i 0 i lt test length i          test i    new int i        System out println Arrays deepToString test         Object   test2       test2   new Object 5    array of objects     for  int i 0 i lt test2 length i          test2 i    new int i    array is a object too      System out println Arrays deepToString test2            Outputs        0    0  0    0  0  0    0  0  0  0         0    0  0    0  0  0    0  0  0  0     The arrays test and test2 are  more or less  the same

User · Answer

If you have this array   String      example       Please     Thanks      Hello     Hey    Hi                                Why     Where     When     Who       Yes         You can do this   example length      2  example 0  length      2  example 1  length      2  example 0  1  length      3  example 1  0  length      4

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length   number of rows   column length    0  length   number of columns   row length

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public class Array 2D   int arr      public Array 2D         Random r new Random 10        arr   new int 5  10        for int i 0 i lt 5 i                    for int j 0 j lt 10 j                            arr i  j   int r nextInt 10                          public void display                for int i 0 i lt 5 i                             for int j 0 j lt 10 j                                    System out print arr i  j                                     System out println                           public static void main String   args         Array 2D s new Array 2D         s display

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With Java 8  allow you doing something more elegant like this   int     foo   new int               new int     1  2  3            new int     1  2  3  4           int length   Arrays stream array  max Comparator comparingInt ArrayUtils  getLength   get   length

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Try this following program for 2d array in java   public class ArrayTwo2       public static void main String   args  throws  IOException NumberFormatException          BufferedReader br new BufferedReader new InputStreamReader System in            int     a          int sum 0          a new int 3  2           System out println  Enter array with 5 elements            for int i 0 i lt a length i                          for int j 0 j lt a 0  length j                              a i  j  Integer parseInt br readLine                                     for int i 0 i lt a length i                          for int j 0 j lt a 0  length j                              System out print a i  j                     sum sum a i  j                         System out println                 System out println  Array Sum    sum           sum 0

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import java util Arrays   public class Main        public static void main String   args                  double     test      100    200    300    400    500    600    700    800    900    1000             int      removeRow      0    1    3    4               double     newTest   new double test length - removeRow length  test 0  length            for  int i   0  j   0  k   0  i  lt  test length  i                  if  j  lt  removeRow length                    if  i    removeRow j  0                         j                        continue                                              newTest k  0    test i  0               k                       System out println Arrays deepToString newTest

User · Answer

There s not a cleaner way at the language level because not all multidimensional arrays are rectangular  Sometimes jagged  differing column lengths  arrays are necessary   You could easy create your own class to abstract the functionality you need   If you aren t limited to arrays  then perhaps some of the various collection classes would work as well  like a Multimap

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Consider  public static void main String   args         int     foo   new int               new int     1  2  3            new int     1  2  3  4               System out println foo length     2     System out println foo 0  length     3     System out println foo 1  length     4     Column lengths differ per row   If you re backing some data by a fixed size 2D array  then provide getters to the fixed values in a wrapper class

User · Answer

It was really hard to remember that       int numberOfColumns   arr length      int numberOfRows   arr 0  length    Let s understand why this is so and how we can figure this out when we re given an array problem  From the below code we can see that rows   4 and columns   3       int     arr      1  1  1  1                          2  2  2  2                          3  3  3  3       arr has multiple arrays in it  and these arrays can be arranged in a vertical manner to get the number of columns  To get the number of rows  we need to access the first array and consider its length  In this case  we access  1  1  1  1  and thus  the number of rows   4  When you re given a problem where you can t see the array  you can visualize the array as a rectangle with n X m dimensions and conclude that we can get the number of rows by accessing the first array then its length  The other one  arr length  is for the columns

User · Answer

Java allows you to create  ragged arrays  where each  row  has different lengths   If you know you have a square array  you can use your code modified to protect against an empty array like this     if  row  gt  0  col   test 0  length

[java] Getting the array length of a 2D array in Java

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