Is there a way to use scanner to read in a full string including the spaces, without reading the ful-CodePudding

Let's say my text file looks like this:

John Doe    18    male
Amy hun     19    female

I need to read this into an array like so

while(reader.hasNextLine()){

    result[i] = new Person(reader.next(),reader.next(),reader.next());
    reader.nextLine();
    i  ;
}

but it keeps messing up my array because it treats each space as a delimiter and does not use it, where the columns are separated by whitespace.

I tried using delimiter to spaces on my scanner but I get the error: Exception in thread "main" java.util.NoSuchElementException. Tried a few things but no luck too. I also can't just read in both names as separate Strings because some rows will only have one name.

CodePudding user response：

You will want to read each line of text, and then parse the line using regex or "regular expressions". The regex is a flexible way of grabbing parts of Strings that match certain rules. For instance, if you iterate through the file line by line, grabbing each line with reader.nextLine():

while (reader.hasNextLine()) {
    String line = reader.nextLine();
    // ...
}

now line holds an line from the file, such as "John Doe 18 male"

Then you will want to split this line into 3 substrings representing the name, age, and sex, and they are represented by text followed by a number followed by text, all split by white space (spaces)

If you call .split(...) on the String, you can use a regex that will divide the String based on these rules:

String regex = "(?<=\\d)\\s |\\s (?=\\d)";

This works because the regular expression, "(?<=\\d)\\s |\\s (?=\\d)" splits at a number followed by white-space: (?<=\\d)\\s or white-space followed by a number: \\s (?=\\d) using regex look-ahead and look-behind rules.

This will split the string into the tokens: {"John Doe", "18", "male"}

The whole thing could look like:

List<Person> personList = new ArrayList<>();

String regex = "(?<=\\d)\\s |\\s (?=\\d)";

while (reader.hasNextLine()) {
    String line = reader.nextLine();
    String[] tokens = line.split(regex);
    Person person = new Person(tokens[0], tokens[1], tokens[2]);
    // or perhaps:
    // Person person = new Person(tokens[0], Integer.parseInt(tokens[1]), tokens[2]);
    personList.add(person);
}

CodePudding user response：

Set your Scanner's delimiter appropriately:

reader.useDelimiter("(?m)(?<=\\d)\\s |\\s (?=\\d)|\n");

With this, you can use your code as-is.

Some test code:

record Person (String name, String age, String gender) {}

public static void main(String[] args) {
    String input ="John Doe    18    male\nAmy hun     19    female\n";
    Scanner reader = new Scanner(input).useDelimiter("(?m)(?<=\\d)\\s |\\s (?=\\d)|\n");
    Person[] result = new Person[10];
    int i = 0;
    while (reader.hasNext()) {
        result[i  ] = new Person(reader.next(), reader.next(), reader.next());
    }
    Arrays.stream(result).filter(Objects::nonNull).forEach(System.out::println);
}

Output:

Person[name=John Doe, age=18, gender=male]
Person[name=Amy hun, age=19, gender=female]