Syntax for creating a two-dimensional array in Java

Question

Consider   int     multD   new int 5     multD 0    new int 10     Is this how you create a two-dimensional array with 5 rows and 10 columns   I saw this code online  but the syntax didn t make sense

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int rows   5  int cols   10   int   multD   new int rows   cols    for  int r   0  r  lt  rows  r        for  int c   0  c  lt  cols  c             int index   r   cols   c       multD index    index   2          Enjoy

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These types of arrays are known as jagged arrays in Java   int     multD   new int 3     multD 0    new int 3   multD 1    new int 2   multD 2    new int 5     In this scenario each row of the array holds the different number of columns  In the above example  the first row will hold three columns  the second row will hold two columns  and the third row holds five columns  You can initialize this array at compile time like below    int     multD     2  4  1    6  8    7  3  6  5  1      You can easily iterate all elements in your array   for  int i   0  i lt multD length  i          for  int j   0  j lt multD i  length  j              System out print multD i  j      t              System out println

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Actually Java doesn t have multi-dimensional array in mathematical sense  What Java has is just array of arrays  an array where each element is also an array  That is why the absolute requirement to initialize it is the size of the first dimension  If the rest are specified then it will create an array populated with default value    int       ar    new int 2     int       ar    new int 2       int       ar    new int 2  2      2x2 array with zeros   It also gives us a quirk  The size of the sub-array cannot be changed by adding more elements  but we can do so by assigning a new array of arbitrary size   int       ar    new int 2  2   ar 1  3    10     index out of bound ar 1       new int    1 2 3 4 5 6      works

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int      twoDim   new int  5  5    int a    twoDim length    5 int b    twoDim 0  length    5  for int i   0  i  lt  a  i        1 2 3 4 5     for int j   0  j  lt b  j         1 2 3 4 5         int x    i 1   j 1           twoDim i  j    x          if  x lt 10                System out print       x                   else               System out print x                          end of for J     System out println       end of for i

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Try   int     multD   new int 5  10     Note that in your code only the first line of the 2D array is initialized to 0  Line 2 to 5 don t even exist  If you try to print them you ll get null for everyone of them

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The most common idiom to create a two-dimensional array with 5 rows and 10 columns is   int     multD   new int 5  10     Alternatively  you could use the following  which is more similar to what you have  though you need to explicitly initialize each row   int     multD   new int 5     for  int i   0  i  lt  5  i        multD i    new int 10

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You can create them just the way others have mentioned  One more point to add  You can even create a skewed two-dimensional array with each row  not necessarily having the same number of collumns  like this   int array       new int 3     array 0    new int 3   array 1    new int 2   array 2    new int 5

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Try the following   int     multi   new int 5  10         which is a short hand for something like this   int     multi   new int 5     multi 0    new int 10   multi 1    new int 10   multi 2    new int 10   multi 3    new int 10   multi 4    new int 10     Note that every element will be initialized to the default value for int  0  so the above are also equivalent to   int     multi   new int          0  0  0  0  0  0  0  0  0  0        0  0  0  0  0  0  0  0  0  0        0  0  0  0  0  0  0  0  0  0        0  0  0  0  0  0  0  0  0  0        0  0  0  0  0  0  0  0  0  0

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We can declare a two dimensional array and directly store elements at the time of its declaration as   int marks       50 60 55 67 70   62 65 70 70 81   72 66 77 80 69      Here int represents integer type elements stored into the array and the array name is  marks   int is the datatype for all the elements represented inside the     and     braces because an array is a collection of elements having the same data type    Coming back to our statement written above  each row of elements should be written inside the curly braces  The rows and the elements in each row should be separated by a commas   Now observe the statement  you can get there are 3 rows and 5 columns  so the JVM creates 3   5   15 blocks of memory  These blocks can be individually referred ta as   marks 0  0   marks 0  1   marks 0  2   marks 0  3   marks 0  4  marks 1  0   marks 1  1   marks 1  2   marks 1  3   marks 1  4  marks 2  0   marks 2  1   marks 2  2   marks 2  3   marks 2  4     NOTE  If you want to store n elements then the array index starts from zero and ends at n-1  Another way of creating a two dimensional array is by declaring the array first and then allotting memory for it by using new operator   int marks                   declare marks array marks   new int 3  5        allocate memory for storing 15 elements   By combining the above two we can write   int marks       new int 3  5

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It is also possible to declare it the following way  It s not good design  but it works   int   twoDimIntArray     new int 5  10

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Try this way   int a         1 2    3 4     int b      1  2  3  4

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In Java  a two-dimensional array can be declared as the same as a one-dimensional array  In a one-dimensional array you can write like    int array     new int 5     where int is a data type  array   is an array declaration  and new array is an array with its objects with five indexes   Like that  you can write a two-dimensional array as the following     int array        array   new int 3  4     Here array is an int data type  I have firstly declared on a one-dimensional array of that types  then a 3 row and 4 column array is created   In your code  int     multD   new int 5     multD 0    new int 10     means that you have created a two-dimensional array  with five rows  In  the first row there are 10 columns  In Java you can select the column size for every row as you desire

[java] Syntax for creating a two-dimensional array in Java

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