Read Data from a File into an ArrayList

File Class

We can use the File class to represent a file.

Constructor

We can create a File object using a String that contains the file path.

File dataFile = new File(filepath);

If the file pile has backslash characters (\), you will need to use two, since this is an escape character.

Scanner Class

You can use the Scanner class to read from a file.

Constructor

The Scanner constructor can be used to create a Scanner object with a File object as the parameter.

Scanner fileScanner = new Scanner(dataFile);

When we create a Scanner object with a File, it is possible for an exception to be thrown if the file path doesn't exist. A try..catch statement can be used.

try(Scanner fileScanner = new Scanner(dataFile)) {
   //statements if the dataFile path exists
} catch (FileNotFoundException error) {
   //statements if the file isn't found
}

Scanner Methods

• hasNextLine() returns true if there is another line in the input of this scanner and false otherwise.
• nextLine() advances the scanner past the current line and returns the input that was skipped.

try(Scanner fileScanner = new Scanner(dataFile)) {
   ArrayList<String> lines = new ArrayList<>();

   while (fileScanner.hasNextLine()) {
      lines.add(fileScanner.nextLine());
   }
   //iterate over lines and separates each entry by comma, 
   //create an object to represent the line with the appropriate data, 
   //add the object to an array that represents the data as objects
} catch (FileNotFoundException error) {
   print("An error has occured.");
}

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