如果我有多个属性，如何读取txt文件？

Question

I am trying to get a class to read my txt file with a few lines, for example:

Facial Lotion, 1 , 2, 0.1

Moisturiser Lotion, 2, 3, 0.2

Toner Lotion, 3, 4, 0.3

Aloe Vera Lotion, 4, 5, 0.4

I created a class call Lotion with attributes name(string), productNo(int), productRating(int), and productDiscount(double, and I create another class call ListOfLotion and add in an arraylist of Lotion.

my problem is how do i get my ListOfLotion class to use the values in txt file and put it in my arraylist.

I tried to use indexOf for name till the next one but i got error, java.lang.StringIndexOutOfBoundsException: begin 0, end -1, length 17

also is there anyway i could separate all four value and make sure they are store properly for example, Facial Lotion is store as the name and 1 is store as prodcuctNo.

public void addListOfLotion(){

    ArrayList<Lotion> lotion = new ArrayList<Lotion>();

    Scanner scanner = new Scanner("Desktop/Lotion.txt");

    while(scanner.hasNext()){

     String readLine = scanner.nextLine();

     int indexProductNo = readLine.indexOf(',');

     int indexOfProductRating = readLine.indexOf(',');

     double indexOfProductDiscount = readLine.indexOf(',');

      lotion.add(new Lotion(readLine.substring(0, indexOfProductNo),0,0,0));

    }scanner.close();

    }

Got this error as result: 
  java.lang.StringIndexOutOfBoundsException: begin 0, end -1, length 17
    at java.base/java.lang.String.checkBoundsBeginEnd(String.java:3319)
    at java.base/java.lang.String.substring(String.java:1874)
    at ListOfVenues.addListOfLotion(ListOfLotion.java:42)

Is it beccause I put readLine,indexOf(',') as every readLine, it just stop at the first ','? Anyway I could effectively let java know that between this and this index is for name, and between this and this index is for productNo?

thanks guys really appreciate it.

Answer 1

You could use a regex ( Demo ):

([\w\s]+)\s*,\s*(\d+)\s*,\s*(\d+)\s*,\s*(\d+(?:\.\d+))

Which you could define as a constant in your class:

private static final Pattern LOTION_ENTRY = 
    Pattern.compile("([\\w\\s]+)\\s*,\\s*(\\d+)\\s*,\\s*(\\d+)\\s*,\\s*(\\d+(?:\\.\\d+))");

Then you can just create a Matcher for every entry and extract the groups:

Matcher matcher = LOTION_ENTRY.matcher(readLine);

if(matcher.matches()) {
    String name = matcher.group(1);
    int no = Integer.parseInt(matcher.group(2));
    int rating = Integer.parseInt(matcher.group(3));
    double discount = Double.parseDouble(matcher.group(4));

    // do something
} else {
    // line doesn't match pattern, throw error or log
}

A note though: the parseInt() and parseDouble can throw a NumberFormatException if the input is not valid. So you'd have to catch those and act accordingly.

Answer 2

Since the lines are comma-separated lists you could use split() to split the line into the single variables.
Another thing to consider is that Scanner("file.txt") doesn't read the indicated text file but just the given String . You have to create a File object first.

File input = new File("Desktop/Lotion.txt");
Scanner scanner;
scanner = new Scanner(input);
while(scanner.hasNext()){
    String readLine = scanner.nextLine();
    String[] strArray = readLine.split(",");
    int indexOfProductNo = Integer.parseInt(strArray[1].trim());
    int indexOfProductRating = Integer.parseInt(strArray[2].trim());
    double indexOfProductDiscount = Double.parseDouble(strArray[3].trim());
    lotion.add(new Lotion(strArray[0],indexOfProductNo,indexOfProductRating,indexOfProductDiscount));
}