A 2D Array Is an Array of Arrays

Java has no built-in rectangular grid type. When you write int[][] g, you're really making an array whose elements are references to other arrays. The outer array holds one reference per row; each row is its own independent int[] array living somewhere in memory. So a grid is an array of arrays, stacked conceptually into rows and columns, but structurally just one array pointing at several others.

This matters for how you measure the grid. g.length counts the elements of the outer array, which are the rows, so it gives the number of rows. To get the number of columns, you have to ask one specific row array how long it is, using g[0].length (or any other valid row index). There is no single property that reports 'columns' directly, because the grid's column count is really just a property of whichever row you check.

This picture carries forward into every grid traversal you write. Nested loops work precisely because the outer loop walks the outer array (rows) and the inner loop walks whichever row array that reference points to (columns). It also explains ragged arrays, where rows can have different lengths, since each row is its own separate array and nothing forces them to match.