Help! Program cannot run. Error is "java.lang.NullPointerException".

[bMorgan]

I want to output the frequency of the words in a sentence. The program can compile, but cannot run. The error is "java.lang.NullPointerException". Thank you very much.


import java.util.Hashtable;
import java.util.StringTokenizer;
import java.util.Enumeration;

public class Main{

public void main(String[] args)
{

WordCount wc = new WordCount();
wc.processLine("da do ro ro ro, da do ro ro");
wc.print ();
}
}

import java.util.Hashtable;
import java.util.StringTokenizer;
import java.util.Enumeration;


public class WordCount
{
Hashtable ht;
public WordCount ()
{
ht = new Hashtable ();
}

public void processLine (String s)
{
StringTokenizer st = new StringTokenizer (s, " ,.");
while (st.hasMoreTokens()) {
String word = st.nextToken();
processWord (word.toLowerCase ());
}
}

public void processWord (String word)
{
if (ht.containsKey (word)) {
Integer i = (Integer) ht.get (word);
Integer j = new Integer (i.intValue() + 1);
ht.put(word, j);
}
else {
ht.put(word, new Integer (1));
}
}

public void print ()
{
Enumeration enum1 = ht.keys ();
while (enum1.hasMoreElements ()) {
String key = (String) enum1.nextElement ();
Integer value = (Integer) ht.get (key);
System.out.println ("{ " + key + ", " + value + " }");
}
}

}

[curmudgeon]

I don't see any NPE when I run it, although I have a hard time running it since the main method is not static. ;)
Which line causes the problem?

[bMorgan]

Thank you for replying. After i add " static ", it works. Thx.

[curmudgeon]

Thank you for replying. After i add " static ", it works. Thx.

Were all problems so easy! :)

You're welcome!