How can I parse lines of data from file to populate objects for each?

Question

I have a text file with the list inside, every line has data that I need insert in the new objects. So data looks like somename=3000 or another type with the slash data another type = 6000.

I have particular class "Item" that has String and int variable. Data need to be inserted into them. Every new object has to be added to the ArrayList<Item>.

// Calculate the lines for next for each loop
int lineCount = 0;
while (sc.hasNextLine()) {
    lineCount++;
    sc.nextLine();
}

for (int i = 0; i < lineCount; i++) {
    // creating the object
    Item item = new Item();
    // add item object to items ArrayList
    items.add(item);

    // add line to String variable lineToString,
    while (scaner.hasNextLine()) {
        String lineToString = scaner.nextLine();
        sc.nextLine();
    }

So, I figured out that to do this, I need to

copy the whole line and put into some string variable;
split it for integer and string variable;
insert string parts to the String variable and numbers to the int variable in particular object that was created in iteration time of "for loop".
add the object with a data inside to the ArrayList.

I used Scanner to read a text file. When I try to insert the scaner.nextLine to the String it's doesn't work; I mean it's executing but variable String lineToString doesn't have the line from a text file.

Could somebody help with an idea of how better to proceed with this problem? Maybe there is some simpler way to insert the 2 different type of data from the text file line in the object and put it into the ArrayList? Every line in the text file has different data and has to be in different objects.

Shafin Mahmud · Accepted Answer · 2018-06-30T17:18:05.410

You didn't mention clearly the line format from the text file. I assume so far you have text file in which each line is like

someone=140000

And you are trying to read those lines of the text and parse each of them to an object of Item which contains a String property (I assume you name it name) and an int property (I assume you name it number)

If this is it, you fisrt need to read your text file line by line and process it further. There are several ways to read a text file line by line.

BufferReader

This is a very common and so far most appropriate way to read a text file in consider of performance.

List<Item> particulatItems = new ArrayList<>();

// using try-with-resource that will help closing BufferedReader by own
try (BufferedReader br = new BufferedReader(new FileReader(file))) {
    String line;
    while ((line = br.readLine()) != null) {
       particularItems.add(processLine(line));
    }
}

Scanner

You could use Scanner too.

try (Scanner scanner = new Scanner(new File(fileName))) {
     while (scanner.hasNext()) {
        particularItems.add(processLine(line));
     }

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

You should extract the line processing logic to a independent function. This is good practice of clean coding.

public static Item processLine(Strinng line) {
     String[] tokens = line.split("=");
     Item item = new Item(tokens[0], tokens[1]);
}

Assuming you have that particular object defined as Item and you are populating a List of this type

 public class Item {
    String name;
    int number;

    public Item(String name, String numtxt) {
       this.name = name;
       this.number = Integer.parseInt(numtxt);
    }

   // setter getter
 }

More reading:

score 0 · Answer 2 · answered Jun 30 '18 at 16:28

0

Looks like you have already scanned full file in below code snippet:

while (sc.hasNextLine()) {
    lineCount++;
    sc.nextLine();
}

After this, you are again iterating in for-loop but with same scanner, which has read last line So the following may return false:

while (scaner.hasNextLine())

I it may never enter while loop

You should reset scanner before iterating lines again .. or may be use something else than scanner to count lines

answered Jun 30 '18 at 16:28

Ashish Mishra

303
4
10

Thank you for an explanation, it was exactly like you said, never entered the while loop. I didn't know why, didn't know that by using that code, you scanning whole file! You really helped bro! – Mykola Rudenko Jun 30 '18 at 17:02
Glad to know if my answer really helped – Ashish Mishra Jun 30 '18 at 17:33

score 0 · Answer 3 · answered Jun 30 '18 at 16:32

0

Apart from what @Ashish Mishra mentioned, you are doing the second while loop in a for loop, why? Isn't one loop sufficient?

    int lineCount = 0;
    while (sc.hasNextLine()) {
        lineCount++;
        String lineToString = sc.nextLine();
        Item item = new Item();
        //convert lineToString to item
        items.add(item);
    }

answered Jun 30 '18 at 16:32

gagan singh

1,591
1
7
12

@Shafin Mahmud posted the perfect solution for this problem. Thanks for the feedback! – Mykola Rudenko Jun 30 '18 at 17:03

How can I parse lines of data from file to populate objects for each?

3 Answers3

BufferReader

Scanner