strange java string array null pointer exception
12,680
Solution 1
Because you made arr
referring to null
, so it threw a NullPointerException
.
EDIT:
Let me explain it via figures:
After this line:
String arr[] = new String[10];
10 places will be reserved in the heap for the array arr
:
and after this line:
arr = null;
You are removing the reference to the array and make it refer to null
:
So when you call this line:
arr[0] = "one";
A NullPointerException
will be thrown.
Solution 2
With arr = null;
you are deleting the reference to the object.
So you can't access it anymore with arr[anynumber]
.
Author by
m0therway
Updated on June 04, 2022Comments
-
m0therway almost 2 years
This problem came up in a practice test: create a new string array, initialize it to null, then initializing the first element and printing it. Why does this result in a null pointer exception? Why doesn't it print "one"? Is it something to do with string immutability?
public static void main(String args[]) { try { String arr[] = new String[10]; arr = null; arr[0] = "one"; System.out.print(arr[0]); } catch(NullPointerException nex) { System.out.print("null pointer exception"); } catch(Exception ex) { System.out.print("exception"); } }
Thanks!