.txt file to arrays using Java

Question

I have a .txt file containing document information (For 1400 documents). Each document has an ID, title, author, area and abstract. A sample looks like this:

.I 1
.T
experimental investigation of the aerodynamics of a
wing in a slipstream .
.A
brenckman,m.
.B
j. ae. scs. 25, 1958, 324.
.W
experimental investigation of the aerodynamics of a
wing in a slipstream .
  [...]
the specific configuration of the experiment .

I want to put each of these into 5 arrays dedicated to each category. I'm having trouble inserting the title and abstract into a single array position, can anyone tell me what's wrong with this code? What I am trying to do is insert the text lines into position x after a ".T" is read and stop when it finds a ".A", when it happens, increase position by 1 for it to fill the next position

try{
    collection = new File (File location);
    fr = new FileReader (collection);
    br = new BufferedReader(fr);
    String numDoc = " ";
    int pos = 0;
    while((numDoc=br.readLine())!=null){
        if(numDoc.contains(".T")){
            while((numDoc=br.readLine())!= null && !numDoc.contains(".A")){
                Title[pos] = Title[pos] + numDoc; 
                pos++;
           }

        }
    }
}
catch(Exception e){
     e.printStackTrace();
}

The goal is to have all the information within a single line of String. Any help would be greatly appreciated.

Answer 1

A code walkthrough is always helpful. In the future, you can probably use breakpoints, but I think I know why you're getting what I assume is a Null Pointer Exception.

while((numDoc=br.readLine())!=null){
    if(numDoc.contains(".T")){
        while((numDoc=br.readLine())!= null && !numDoc.contains(".A")){

Outside, everything looks good, In this loop is where the things start going bonkers.

            Title[pos] = Title[pos] + numDoc; 

With your provided input, we would set:

Title[0] as Title[0] + "experimental investigation of the aerodynamics of a"

This works only if Title[0] exists, which I don't assume it has been initialized, yet. We'll address that issue first by correctly detecting for a null array value. This would either be a compiler error about something not being initialized or a run-time null pointer exception. Off the top of my head, I want to say compiler error.

So anyways, we'll address dealing with null Title[pos].

while((numDoc=br.readLine())!=null){
    if(numDoc.contains(".T")){
        while((numDoc=br.readLine())!= null && !numDoc.contains(".A")){
            if(Title[pos] != null) {
                Title[pos] = Title[pos] + numDoc; 
            }
            else {
                Title[pos] = numDoc;
            }
            pos++;
       }
    }
}

When we do another walkthrough, we'll get the following array values

Title[0]=experimental investigation of the aerodynamics of a

Title[1]=wing in a slipstream .

If this intended, then this is fine. If you wanted the titles together, then you move the pos++ out the while loop.

while((numDoc=br.readLine())!=null){
    if(numDoc.contains(".T")){
        while((numDoc=br.readLine())!= null && !numDoc.contains(".A")){
            if(Title[pos] != null) {
                Title[pos] = Title[pos] + " " + numDoc; // add a space between lines
            }
            else {
                Title[pos] = numDoc;
            }
       }
       pos++;
    }
}

Then we get:

Title[0]=experimental investigation of the aerodynamics of a wing in a slipstream .

You may want to trim your inputs, but this should cover both of the potential errors that I can see.