Hi there, I posted this question earlier but not with the code in its entirety. The coe below also calls to other classes Background and Hydro which I have included at the bottom.

I have a Nullpointerexception at the line indicate by asterisks. Which would suggest to me that the Collections are not storing data properly. Although when I check their size they seem correct.

Thanks in advance. PS: If anyone would like to give me advice on how best to format my code to make it readable, it would be appreciated.

Elliott

package exam0607;

import java.io.BufferedReader; import java.io.IOException; import java.io.InputStream; import java.io.InputStreamReader; import java.net.URL; import java.util.Collection; import java.util.Scanner; import java.util.Vector;

import exam0607.Hydro; import exam0607.Background;// this may not be necessary???? FIND OUT

public class HydroAnalysis {

public static void main(String[] args) {

Collection hydroList = null; Collection backList = null;

try{hydroList = readHydro("http://www.hep.ucl.ac.uk/undergrad/3459/exam_data/2006-07/final/hd_data.dat");} catch (IOException e){ e.getMessage();} try{backList = readBackground("http://www.hep.ucl.ac.uk/undergrad/3459/exam_data/2006-07/final/hd_bgd.dat"); //System.out.println(backList.size()); }

catch (IOException e){ e.getMessage();}

for(int i =0; i <=14; i++ ){ String nameroot = "HJK";
String middle = Integer.toString(i); String hydroName = nameroot + middle + "X"; System.out.println(hydroName); ALGO_1(hydroName, backList, hydroList); } }

public static Collection readHydro(String url) throws IOException { URL u = new URL(url); InputStream is = u.openStream(); InputStreamReader isr = new InputStreamReader(is); BufferedReader b = new BufferedReader(isr); String line ="";

Collection data = new Vector(); while((line = b.readLine())!= null){ Scanner s = new Scanner(line); String name = s.next(); System.out.println(name); double starttime = Double.parseDouble(s.next()); System.out.println(+starttime); double increment = Double.parseDouble(s.next()); System.out.println(+increment); double p = 0; double nterms = 0;

while(s.hasNextDouble()){ p = Double.parseDouble(s.next()); System.out.println(+p); nterms++; System.out.println(+nterms);
} Hydro SAMP = new Hydro(name, starttime, increment, p); data.add(SAMP);
} return data; }

public static Collection readBackground(String url) throws IOException { URL u = new URL(url); InputStream is = u.openStream(); InputStreamReader isr = new InputStreamReader(is); BufferedReader b = new BufferedReader(isr); String line =""; Vector data = new Vector(); while((line = b.readLine())!= null){ Scanner s = new Scanner(line); String name = s.next();
//System.out.println(name); double starttime = Double.parseDouble(s.next()); //System.out.println(starttime); double increment = Double.parseDouble(s.next()); //System.out.println(increment); double sum = 0; double p = 0; double nterms = 0; while((s.hasNextDouble())){ p = Double.parseDouble(s.next()); //System.out.println(p); nterms++; sum += p; } double pbmean = sum/nterms; Background SAMP = new Background(name, starttime, increment, pbmean); //System.out.println(SAMP); data.add(SAMP);
} return data; }

public static void ALGO_1(String hydroName, Collection backgs, Collection hydros){ //double aMin = Double.POSITIVE_INFINITY; //double sum = 0; double intensity = 0; double numberPN_SIG = 0; double POSITIVE_PN_SIG =0; //int numberOfRays = 0; for(Hydro hd: hydros){ System.out.println(hd.H_NAME); for(Background back : backgs){ System.out.println(back.H_NAME); if(back.H_NAME.equals(hydroName)){//ERROR HERE double PN_SIG = Math.max(0.0, hd.PN - back.PBMEAN); numberPN_SIG ++; if(PN_SIG > 0){ intensity += PN_SIG; POSITIVE_PN_SIG ++; } }
} double positive_fraction = POSITIVE_PN_SIG/numberPN_SIG; if(positive_fraction < 0.5){ System.out.println( hydroName + "is faulty" ); } else{System.out.println(hydroName + "is not faulty");} System.out.println(hydroName + "has instensity" + intensity); }

} }

THE BACKGROUND CLASS

package exam0607; public class Background {

String H_NAME; double T_START; double DT; double PBMEAN;

public Background(String name, double starttime, double increment, double pbmean) {

name = H_NAME; starttime = T_START; increment = DT; pbmean = PBMEAN;

}}

AND THE HYDRO CLASS

public class Hydro {

String H_NAME; double T_START; double DT; double PN; public double n;

public Hydro(String name, double starttime, double increment, double p) {

name = H_NAME; starttime = T_START; increment = DT; p = PN; }

}