Null pointer access: The variable can only be null at this location

Question

for(int i=0;i<n;i++){
  for(int j=0;j<26;j++){
    if(str.charAt(i)== strChar.charAt(j) )
    * strSet1.append(str.charAt(i));
  }
    * strSet2.append(str.charAt(i));
}

Exception:

Exception in thread "main" java.lang.NullPointerException
  at AterSeries.main(AterSeries.java:33)

why this code gives null pointer exception

warning: Null pointer access: The variable strSet1 can only be null at this location Null pointer access: The variable strSet2 can only be null at this location

Grondin

Please provide the entire warning message, and mark the line where it's occurring. – Jollenta

this means the length of your str string is less than either n or 26 – Felker

I think your inner loop condition isn't right. what is your string length? – Ferrick

@TusharGupta: In that case it would throw IndexOutOfBoundsException. NPE is thrown when you call a method on a null object for instance. – Beaujolais

str is n which is input and strChar is 26 alphabates – Grondin

Answer 1

Are strSet1 and strSet2 initialized before this? If they are null, you'd get a NullPointerException.

* EDIT *

You cannot call .append() (or any other method) on a variable that is null. Initialize them as:

StringBuffer strSet1 = new StringBuffer();
StringBuffer strSet2 = new StringBuffer();

Beaujolais

initially Yes, all three variable are initialize with null, so what should i do? @tomppa – Grondin

See updated answer, you cannot call methods on null objects. – Beaujolais

latter str contains input and strChar is not null-it contains 26 alhabates @tomppa – Grondin

What about strSet1 and strSet2? – Beaujolais

of course, str is less than 26 but str String is equal to n @Tusar gupta – Grondin

strSet1 and strSet2 is BufferString with null -- @tomppa – Grondin

Thus you can fix the program by initializing them like shown above (edited answer again). – Beaujolais