Java.lang.NullPointerException : Where is the bug ?!

Question

Hi,
where is the bug in this method ?
I just do not see it !
When I run it I get the following error message
Exception in thread "main" java.lang.NullPointerException
at edu.clip.rerank.main.packageRec(main.java:239)
and line 239 is the one I have indicated with <================
Any suggestion would be immensely appreciated.
Many thanks.
public static RerankInstance packageRec (ArrayList chunk)
String spanish = new String();
String gold = new String();
String line = null;
boolean readingCandidates = false;
Double lm = null;
Double tm = null;
Double lm_tm = null;
ArrayList candidates = new ArrayList();
ArrayList LM_likelihoods = new ArrayList();
ArrayList TM_likelihoods = new ArrayList();
ArrayList LM_TM_likelihoods = new ArrayList();
RerankInstance foo = null;
for (int i = 0; i < chunk.size(); i++) {
if (!chunk.get(0).toString().startsWith("<REC>")) {
System.out.println("PROBLEM DETECTED " + chunk.get(0));
line = chunk.get(i).toString();
if (line.startsWith("Spanish=")) {
spanish = line.substring("Spanish=".length());
System.out.println("SPANISH== " + spanish);
else if (line.startsWith("Gold="))
gold = line.substring("Gold=".length());
else if (line.startsWith("<CANDIDATES>"))
readingCandidates = true;
else if (line.startsWith("</CANDIDATES>"))
readingCandidates = false;
if (spanish != null && candidates.size() > 0) {
System.out.println("Spanish=" + spanish);
String [] cands = (String[]) candidates.toArray(new String[0]);
foo = new RerankInstance (spanish, cands);
ArrayList LM_temp = new ArrayList();
ArrayList TM_temp = new ArrayList();
ArrayList LM_TM_temp = new ArrayList();
if (LM_likelihoods.size() > 0 )
Double [] LM_likes = (Double[])LM_likelihoods.toArray(new Double[0]);
foo.setLikelihoods_single(LM_likes);
if (TM_likelihoods.size() > 0 ){
Double [] TM_likes = (Double[])TM_likelihoods.toArray(new Double[0]);
foo.setLikelihoods_single(TM_likes);
if (LM_TM_likelihoods.size() > 0 ) {
Double [] LM_TM_likes = (Double[])LM_TM_likelihoods.toArray(new Double[0]);
foo.setLikelihoods_single(LM_TM_likes);
}//if
else if (readingCandidates) {
System.out.println("Candidate[" + line + "]");
int ndx = line.indexOf('\t');
candidates.add(line.substring(0,ndx));
int ndx_a = line.indexOf('\t', ndx+1);
int ndx_b = line.indexOf('\t', ndx_a+1);
if (ndx_a > ndx+1) {
lm = (line.substring(ndx+1,ndx_a)).startsWith("-Infinity") ? new Double(0) : new Double (line.substring(ndx+1,ndx_a));
if (ndx_b > ndx_a+1) {
tm = (line.substring(ndx_a+1,ndx_b)).startsWith("-Infinity") ? new Double(0) : new Double(line.substring(ndx_a+1,ndx_b));
if ( ndx_b > -1) {
lm_tm = (line.substring(ndx_b+1)).startsWith("-Infinity") ? new Double (0) : new Double(line.substring(ndx_b+1));
try
if (lm != null)
LM_likelihoods.add(lm);
if (tm != null)
TM_likelihoods.add(tm);
if (lm_tm != null)
LM_TM_likelihoods.add(lm_tm);
} catch (Exception e){ };
}//else
}//for
String test = foo.getSourcePhrase().getPhrase(); <==============
System.out.println("WHERE IS THE SOURCE " + test);
return foo;
} //end of method

Answer 1

Foo is definatelly null because...
Near the begining of the method foo is initialised to null.
A load of conditional statements follow in only one of which foo is instantiated.
If this condition is not satisfied foo will remain null.
If that happens then you will get the error that you're getting on line 239.
Essentially all the conditions before the above mentioned condition would have to evaluate to false for foo not to remain null by the time line 239 is executed.
Line 239 is executed regardles of any of the conditional statements in your method, i.e. regardless of whether null is instantiated or not, in which case it remains null - hence the NullPointerException.