I have a code
String ejgStr[] = new String[][]{{null},new String[]{"a","b","c"},{new String()}}[0] ;
System.out.println(ejgStr[0]);
which compiles without error. From what I understand you can't create an array with non-matching square brackets.
On the left, we have String ejgStr[], which is 1-d array and
On the right, we have String[][]{some array}[0], which is 2-d array
These seem to have different dimensions but why do they successfully compile?
You are assigning a one-dimensional String[] array to the first dimension of an inline two-dimensional String[][] array. Have a look the comments:
String ejgStr[] =
new String[][] {
{ null }, // a null 1D String array
new String[] {"a","b","c"}, // a 1D String array containing a,b,c
{ new String() } // a String array containing empty String
}[0]; // access the { null } 1D array
I expect your assignment to be equivalent to doing this:
String ejgStr[] = { null };
You assign a 1D array to the ejgStr refference. If you look at the end of the first statemend, you will see that you have a [0] index specified which means you will assign the first array (position 0) to your referrence. If you remove the [0] you will receive a compilation error.
new String[][]{...} is a 2D array.
new String[][]{...}[0] is the first element of a 2D array, which is a 1D array.
That's what you're assigning to String ejgStr[].
String ejgStr[] is just a reference to a variable in heap space.
you're pointing to first dimensional of 2D-dimensional array using [0] and make a reference of it in ejgStr[]. this is not common to get 1D from 2D array, but you can do it if you need and of course it wont make compile error.
String[] ejgStr =. The other allowed notation was added for compatibility with C/C++, and is a dead giveaway of a novice or C/C++ programmer. ;)