String array list using Scanner

Question

Edit: added the braces {} and an Eclipse screenshot

I have a problem with a simple assignment to create a class that has an array list to store words from the command-line, with each word appended to the end of the array list, then search the list for a specific word ("the") and prints location of the word's occurences, plus another method to return a new array list with the words at the positions specified by a number.

I wrote the code below. In Eclipse IDE, it doesn't show any errors, but when I tried to run the code by Run Configurations and enter this dummy text: "The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the lazy dog.", it doesn't work. I'm not sure why, could you give me advice? Thank you!

import java.util.ArrayList;
import java.util.Scanner;
class Search {
    ArrayList<String> list;

    public Search(){
        list = new ArrayList<String>();
    }

    public void read(){
        Scanner scanner = new Scanner(System.in);
        while(scanner.hasNext()) {
            list.add(scanner.next());
        }
        scanner.close();
    }

    public void find(String word){
        for(int i = 0; i < list.size(); i++) {
            if(list.get(i).equalsIgnoreCase(word)) {
                System.out.println(i);
            }
        }
    }

    public ArrayList<String> subsequence(int[] positions){
        ArrayList<String> result = new ArrayList<String>();
        for(int i = 0; i < positions.length; i++) {
            if(positions[i] >= 0 && positions[i] < list.size()) {
                result.add(list.get(positions[i]));
            }   
        }
        return result;
    }

    // Testing method within class again
    public static void main(String[] args){
        Search search = new Search();
        search.read();
        search.find("the");
        for(String s : search.subsequence(new int[]{0, 3, 4}))
            System.out.println(s);

    }
}  

Answer 1

• As dear @Chris commented kindly use the braces while coding. I run your code in two different ways and I got the output.

• First Way

• If you want to use scanner.hashNext() with while then you should change your main() and read() like this

  public static void main(String[] args) {
      Search search = new Search();
      Scanner sc = new Scanner(System.in);
      String line = sc.nextLine();
      sc.close();
      search.read(line);
      search.find("the");
      for (String s : search.subsequence(new int[] { 0, 3, 4 })) {
          System.out.println(s);
      }
  }
  
  public void read(String line) {
          Scanner scanner = new Scanner(line).useDelimiter("\\s");
          while (scanner.hasNext()) {
              list.add(scanner.next());
          }
          scanner.close();
  }
  
  

• A simple text scanner which can parse primitive types and strings using regular expressions.

• A Scanner breaks its input into tokens using a delimiter pattern, which by default matches whitespace. The resulting tokens may then be converted into values of different types using the various next methods.

• The next() and hasNext() methods and their primitive-type companion methods first skip any input that matches the delimiter pattern, and then attempt to return the next token. Both hasNext() and next() may block waiting for further input. Whether a hasNext() block has no connection to whether or not its associated next method will block.

• Second Way

• If you want to use StringTokenizer then you should have to change just read() to your existing code.

  public void read(String line) {
      Scanner scanner = new Scanner(System.in);
      StringTokenizer st = new StringTokenizer(scanner.nextLine(), " ");
      while (st.hasMoreElements()) {
          list.add(st.nextElement().toString());
      }
      scanner.close();
  }
  

• It is always better to use StringTokenizer for the string. The StringTokenizer class allows an application to break a string into tokens.

• A StringTokenizer object internally maintains a current position within the string to be tokenized. Some operations advance this current position past the characters processed. A token is returned by taking a substring of the string that was used to create the StringTokenizer object.

Reference : Scanner and StringTokenizer