Read file Scanner Method. then make array list in main

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I am new to java and I am having trouble with this. I need to read a txt file full of integers in a method and then I am supposed to call it in the main to make an ArrayList. I can't seem to figure it out.

this is what i have.

public class num {
    public static void main(String[] args) {
        ArrayList<Integer> list = new ArrayList<Integer>();
        list=  getFile();
        System.out.println("numbers are: " + list);
    }

    public static void getFile() {

        try {
            Scanner read = new Scanner(new File("numbers.txt"));

            do {
                int line = read.nextInt();
            }while (read.hasNext());

        } catch (FileNotFoundException fnf) {
            System.out.println("File was not found");
        }

        return line;
    }
}

Try this:

public class num {
public static void main(String[] args) {
    ArrayList<Integer> list = new ArrayList<Integer>();
    getFile(list);
System.out.println("numbers are: " + list);
}

public static void getFile(ArrayList<Integer> list) {


    try {
        Scanner read = new Scanner(new File("numbers.txt"));

        do {
        list.add(read.nextInt());


        }while (read.hasNext());



    } catch (FileNotFoundException fnf) {
        System.out.println("File was not found");
    }

}

Basically, your getFile() method is of type void so it won't return anything. So, you would need to pass your list as a parameter inside this method and then mutate that list. The changes you can then view in your main method.

Java: Read a File into an ArrayList, There are many ways to go about Reading and Writing Files in Java. As nice and simple as the previous method was, it's only useful for reading the file line Using Scanner can be as simple or as hard as the developer wants to make it. void main(String[] args) throws IOException, ClassNotFoundException { // The file​  There are many ways to read a file in Java. Once we read a file, we can perform a lot of operations on the content of that file. Some of these operations, like sorting, may require processing the entire content of the file into memory. In order to perform such operations, we may need to read the file as an Array or a List of lines or words.

You need to change the return type of your method to List and store each nextInt in a local ArrayList and you must return the local list at the end !

public class num {
    public static void main(String[] args) {
        ArrayList<Integer> list = getFile();
        list.forEach(System.out::println);
    }

    public static List<Integer> getFile() {
        List res = new ArrayList<Integer>();
        try {
            Scanner read = new Scanner(new File("numbers.txt"));
            do {
                res.add(read.nextInt());
            }while (read.hasNext());
        } catch (FileNotFoundException fnf) {
            System.out.println("File was not found");
        }
        return res;
    }
}

Read a File into an ArrayList, A quick tutorial to reading files into ArrayLists in Java. However, if we want to provide custom character encoding and byte buffer size, we can use InputStreamReader or Similar to BufferedReader, Scanner provides readLine() method to read an entire line. readAllLines(Paths.get(filename), charset);  3. inside this main methods we will create 3 objects of the class Person. Then, we create an ArrayList name people and add those 3 Person objects. Now, we are ready to write this Arraylist into a file. Write an object into a file. We add this code to the main method.

How to read a text file into ArrayList in Java, All you need to do is read each line and store that into ArrayList, as shown in following example: BufferedReader bufReader = new BufferedReader(new FileReader("file. txt")); ArrayList<String> listOfLines = new ArrayList<>(); String line = bufReader. As noted on How to get input from User, Scanner is also an easy way to read user input using System.in (InputStream) as source.Main advantage of using Scanner for reading file is that it allows you to change delimiter using useDelimiter() method, So you can use any other delimiter like comma, pipe instead of white space.

Writing to a file, We can construct an instance of PrintWriter by specifying the file we want to write to. This program will read from System.in and write whatever you type to a file Scanner; public class TextEditor { public static void main(String[] args) throws To avoid clobbering an existing file, you can always use the exists() method of  Scanner is text parser which used to parse primitives & strings using regular expression. Scanner split the input into token using delimiter pattern. Default pattern delimiter is whitespace. We will write content to a file using FileWriter class. Then, we will read content from as file using Scanner class. Scanner class extends object

[PDF] ArrayList<String> list, Then create and return an array with all the words except the plural words. • Can we Scanner input = new Scanner(new File("data.txt")); while (input.hasNext()) { ArrayList methods (10.1) add(value) list's size() - 1. – Reading or writing any index outside this range will cause an Exception in thread "main" java.lang. Using that constructor you can read a file in Java using Scanner. One other benefit of using Scanner is that it has a useDelimiter() method, using this method file delimiter can be set thus making Scanner a good choice for reading and parsing CSV, tab delimited or pipe symbol separated files in Java.

ArrayList in java with example programs, Here is the list of ArrayList tutorials published on beginnersbook.com. Get/​Search in ArrayList · Override toString() method – ArrayList why can't we add elements outside of main() method? Please read this tutorial if any one want to know  1) reading in the file contents into a list of Strings and. 2) reading in the file contents into a list of String and then creating an array of Strings based on the size of the List and populating that array with the List of String. This is part of a much larger article about how to read files in Java.

Comments
  • You need to return something from the method so it shouldn't be void (Think about what you need it to return. You'll want to do something like ArrayList<Integer> list = getFile(); in the main)
  • Hey thank you this worked perfectly