I already know that how to initialize two dimensional array. But I don't figure out it why.For ex:
I think the initialization should be :
int [][]b=new int[][5];
instead of
int [][]b=new int[5][];
based on following reasons:
assume int[] ==Class A
A b[]=new A[5];
when I replace A with int [],the outcome is
(int[])b=new (int[])[5];
So where I miss the point? Thanks a lot .
A two-dimensional array in Java is just an array of arrays. It's easier to understand if we visualise the first-level array as holding the rows of a matrix, and the second-level array as holding the columns in each row - this makes sense, because when we access an element in position m[i][j] we're referring to the row i and the column j. When we write this:
int[][] b = new int[5][];
… We're stating that the array will have 5 rows, but we don't know in advance how many columns will have each row (this number can be variable!). On the other hand, when we say this:
int[][] b = new int[5][5];
… We're stating from the beginning that there will be 5 rows, each one with 5 columns. Now you can see why this doesn't make sense:
int[][] b = new int[][5];
… It'd be like saying: we want to have 5 columns, but we don't know how many rows there will be - and remember, a two-dimensional array is an array of rows, where each row contains another array representing the columns in that row.
new int[M][N]means "a length-M array of length-N arrays", not vice versa.