New to Java

I'm extremly new at java so please excuse my ignorance I am sure there is some form of built in method to do this.
I am attempting to make an error message using JOptionPane. The following code works fine as long as an integer is put into the dialog box.

String numString = JOptionPane.showInputDialog(null,
   "How many values would you like to swap?" ,
   "Enter a number of values for array to hold", JOptionPane.QUESTION_MESSAGE);

 // Convert string into integer
int number = Integer.parseInt(numString);

But I am attempting to catch invalid input such as:
1. the user hits enter without typing anything ( )
2. a character value is entered instead of a integer (du)
3. a space is acidently inserted into a valid integer ( 8 8

When invalid input is typed I would like to display an error message. I have attempted many different approaches but all has failed but I am certian that there must be some way of doing this

This is the code I was hopeing would work but it doesn't

String numString = JOptionPane.showInputDialog(null,
   "How many values would you like to swap?" ,
   "Enter a number of values for array to hold", JOptionPane.QUESTION_MESSAGE);
    
if (Integer.parseInt (numString) == null)
   JOptionPane.showMessageDialog(null,
    "invalid entry",
    "invalid entry",JOptionPane.INFORMATION_MESSAGE);

else
 // Convert string into integer
int number = Integer.parseInt(numString);