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Author

Need help with NullPointerException

Robert, Assaad
Greenhorn

Joined: Aug 27, 2001
Posts: 12
I get this error at the end of my code execution. Could anyone tell me why and how I fix it.
<message>
java.lang.NullPointerException
at java.util.StringTokenizer.<init>(StringTokenizer.java:122)
at java.util.StringTokenizer.<init>(StringTokenizer.java:138)
at App3.<init>(App3.java:20)
at App3.main(App3.java:42)
</message>
<code (App3.java)>
import java.io.*;
import java.util.*;
public class App3 {
public App3 ( ) throws IOException, NullPointerException {
BufferedReader br = new BufferedReader(new FileReader(new File("data.txt")));
BufferedWriter out = new BufferedWriter(new FileWriter(new File("finalTest.txt")));
String c="| |";
int temp;
StringTokenizer st;
String line;

//while((line = br.readLine()) != null){
while(true){

//if( (line=br.readLine()) == null) break;
st = new StringTokenizer(br.readLine(),c);
temp = st.countTokens();

System.out.println("The Number of tokens found: " + temp);

for(int i = 0; i < temp; i++){

if(st.countTokens()!=0){
System.out.println(" " + st.nextElement());
//out.write(" " + st.nextElement());
} else{
System.out.println(" ");
//out.write(" " + st.nextToken());
} // end if
} //for

} //end while

} //end of constructor
public static void main ( String args[] ) throws IOException, NullPointerException {
new App3();
}//End of Main Method
} // End of Application
</code>
<My Text file contains (data.txt)>
PM1|null|null|11|XX|PID1|HOT1|PLAZA1|NO. 41|Main Description1|
PM2|null|null|12|XX|PID2|HOT2|PLAZA2|NO. 42|Main Description2|
PM3|null|null|13|XX|PID3|HOT3|PLAZA3|NO. 43|Main Description3|
</My Text file contains (data.txt)>
Ganesh Ram
Ranch Hand

Joined: Jul 20, 2001
Posts: 33
NullPointerException's are thrown when operation is performed on a null value.
You should not throw it. You have to prevent it from happening.
One way is check if a value is null before doing anything with it.
For eg: if you have a null string. If you do a string.length(), this will throw a nullpointerexception.
Talisman
Greenhorn

Joined: Sep 11, 2001
Posts: 2
Hi ,

Instead of using " while(true)" why don't u try some more logical comparision like while(st.hasMoreTokens()) .....I hope that will help u out ....

regards
 
It is sorta covered in the JavaRanch Style Guide.
 
subject: Need help with NullPointerException