Which comes first in a 2D array rows or columns

Question

When creating a 2D array  how does one remember whether rows or columns are specified first

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Instinctively one thinks geometrically  horizontal  X  axis and then vertical  Y  axis  This is not  however  the case with a 2D array  rows come first and then columns   Consider the following analogy  in geometry one walks to the ladder  X axis  and climbs it  Y axis   Conversely  in Java one descends the ladder  rows  and walks away  columns

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All depends on your visualization of the array  Rows and Columns are properties of visualization  probably in your imagination  of the array  not the array itself    It s exactly the same as asking is number  5  red or green   I could draw it red  I could draw it greed right  Color is not an integral property of a number  In the same way representing 2D array as a grid of rows and columns is not necessary for existence of this array    2D array has just first dimention and second dimention  everything related to visualizing those is purely your flavour   When I have char array char 80  25   I may like to print it on console rotated so that I have 25 rows of 80 characters that fits the screen without scroll    I ll try to provide viable example when representing 2D array as rows and columns doesn t make sense at all  Let s say I need an array of 1 000 000 000 integers  My machine has 8GB of RAM  so I have enough memory for this  but if you try executing var a   new int 1000000000   you ll most likely get OutOfMemory exception  That s because of memory fragmentation - there is no consecutive block of memory of this size  Instead you you can create 2D array 10 000 x 100 000 with your values  Logically it is 1D array  so you d like to draw and imagine it as a single sequence of values  but due to technical implementation it is 2D

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While Matt B s may be true in one sense  it may help to think of Java multidimensional array without thinking about geometeric matrices at all   Java multi-dim arrays are simply arrays of arrays  and each element of the first- dimension  can be of different size from the other elements  or in fact can actually store a null  sub -array   See comments under this question

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In java the rows are done first  because a 2 dimension array is considered two separate arrays  Starts with the first row 1 dimension array

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In c    distant  dusty memory  I think it was a little easier to look at the code and understand arrays than it is in Java sometimes   Both are row major   This illustration worked for me in helping to understand  Given this code for a 2d array of strings        String     messages       messages   new String                 quot CAT quot   quot DOG quot   quot YIN quot   quot BLACK quot   quot HIGH quot   quot DAY quot              quot kitten quot   quot puppy quot   quot yang quot   quot white quot   quot low quot   quot night quot                    int row   messages length      int col   messages 0  length        Naming my ints as if it were a 2d array  row  col  we see the values  row    int  2 col    int  6  The last two lines of code  where we try to determine size and set them to row and col does not look all that intuitive and its not necessarily right  What youre really dealing with here is this  note new variable names to illustrate   int numOfArraysIn   messages length  int numOfElementsIn0   messages 0  length  int numOfElementsIn1   messages 1  length   Where messages length tells you messages holds two arrays  An array of arrays  AND then messages x  length yields the size of each of the individual arrays 0 1 inside messages  numOfArraysIn    int  2 numOfElementsIn0    int  6 numOfElementsIn1    int  6  When we print with a for each loop     for  String str   messages 0           System out print str   for  String str   messages 1           System out print str    CATDOGYINBLACKHIGHDAYkittenpuppyyangwhitelownight  Trying to drop the brackets and print like this gives an error for  String str   messages          System out print str    incompatible types  String   cannot be converted to String  The above is important to understand while setting up loops that use  length to limit the step thru the array

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In TStringGrid cells property Col come first  Property Cells ACol  ARow  Integer   string read GetCells write SetCells   So the assignment StringGrid1 cells 2  1      abcde   the value is displayed in the third column second row

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The best way to remember if rows or columns come first would be writing a comment and mentioning it  Java does not store a 2D Array as a table with specified rows and columns  it stores it as an array of arrays  like many other answers explain  So you can decide  if the first or second dimension is your row  You just have to read the array depending on that  So  since I get confused by this all the time myself  I always write a comment that tells me  which dimension of the 2d Array is my row  and which is my column

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In Java  there are no multi-dimension arrays  There are arrays of arrays  So   int     array   new int 2  3     It actually consists of two arrays  each has three elements

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Java is considered  row major   meaning that it does rows first  This is because a 2D array is an  array of arrays    For example     int       a   new int 2  4       Two rows and four columns   a 0  0  a 0  1  a 0  2  a 0  3   a 1  0  a 1  1  a 1  2  a 1  3    It can also be visualized more like this   a 0  - gt    0   1   2   3  a 1  - gt    0   1   2   3    The second illustration shows the  array of arrays  aspect  The first array contains  a 0  and a 1    and each of those is an array containing four elements    0  1  2  3     TL DR summary   Array number of arrays  how many elements in each of those arrays    For more explanations  see also Arrays - 2-dimensional

[java] Which comes first in a 2D array, rows or columns?

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