How does Java define a two-dimensional array?

You can also initialize a two-dimensional array definition array using [] [] in Java

Here are some examples
Float[][] Numthree;             Defines a 2-dimensional array of type float
Numthree=new float[5][5];       Allocate 5 rows and 5 columns to the space size
numthree[0][0]=1.1f;            Access 1 rows and 1 columns through the subscript index     =1.1
Long[][] Numfive=new long[5][];     Defines a long type of irregular array
Numfive[0]=new long[5];             Assign 5 columns to line 1th
Defines an array of type Double assigns 3 rows and 3 columns of space at the same time to assign values
Double[][] numsix={{1.111d,2.222d,3.333d},{4.444d,5.555d,6.666d}};

Int[][] Numseven=new int[][]{{10,20,30},{40,50},{60}};

How does Java define a two-dimensional array?