How to check a null position in the vector

Question

Why do if(array[i] == null) is not correct?

What would be the best way to check if that vector space is "empty"?

Answer 1

There is a fundamental difference between a null matrix and an empty matrix . This is a test for null .

int arr[] = null;
if (arr == null) {
  System.out.println("array is null");
}

For you check matrix is empty use;

arr = new int[0];
if (arr.length == 0) {
 System.out.println("array is empty");
}

An alternative definition of " empty " is , if all elements are null :

Object arr[] = new Object[10];
boolean empty = true;
for (int i=0; i<arr.length; i++) {
  if (arr[i] != null) {
    empty = false;
    break;
  }
}

Or;

Object arr[] = new Object[10];
boolean empty = true;
for (Object ob : arr) {
  if (ob != null) {
    empty = false;
    break;
  }
}  

Elements in primitive matrices cannot be empty. They are always initialized for something ( usually 0 for int matrices , but it depends on how you declare the matrix ) .

If you declare the matrix like this, for example:

Reference Here.

int [] myArray ;
myArray = new int[7] ;

All elements will be the default for 0 . An alternative syntax for declaring matrices is

int[] myArray = { 12, 7, 32, 15, 113, 0, 7 };

Where the initial values for a matrix ( of size seven in this case ) are given in the keys { }.

Reference Here.

Answer 2

Considering what you said in this comment:

the vector is of type int - Dr.G

The problem is this:

The type of the array is int[]. Which means that array[i] is the type int. The problem is to compare int with null. Primitive types will never be null and the compiler knows it. So it will give you a build error:

incomparable types: int and <null>