Find all anagrams to a given word from a text file

Question

This program I made takes a word as an input and prints all the anagrams of the word in a given word base from a txt file. I would like advice for code style, Java specific practices etc as I'm new to to the Java language (about 2 months).

import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Scanner;

public class Anagrams {
    public static void main(String[] args) throws FileNotFoundException {
        Scanner s = new Scanner(new File("bg.txt"));

        ArrayList<String> words = new ArrayList<String>();
        while (s.hasNext()) {
            words.add(s.next());
        }

        HashMap<String, ArrayList<String>> map = new HashMap<>();

        for (String str : words) {
            char[] temp = str.toCharArray();
            Arrays.sort(temp);
            String key = new String(temp).toLowerCase();
            if (map.get(key) != null) {
                map.get(key).add(str.toLowerCase());
            } else {
                ArrayList<String> anagramList = new ArrayList<>();
                anagramList.add(str);
                map.put(key, anagramList);
            }
        }
        Scanner input = new Scanner(System.in);
        String str = input.next();
        char[] key = str.toCharArray();
        Arrays.sort(key);
        str = new String(key).toLowerCase();
        if (!map.containsKey(str)) {
            System.out.print("word not found");
        } else if (map.get(str).size() != 1) {
            for (String p : map.get(str)) {
                System.out.print(p + " ");
            }
        } else {
            System.out.print("No anagrams found");
        }
        s.close();
        input.close();
    }
}

Answer 1

Use more functions

The current implementation is all in the main method. Break the problem down to smaller pieces, so that each function has a single responsibility, for example:

• Read words from a text file into a List and return it
• Convert a word to "normalized" form (sorted and lowercased)
• Convert a list of words to a map of normalized form to list of anagrams
• Read input and respond with the list of anagrams

Use interface types instead implementations

Instead of these:

ArrayList<String> words = new ArrayList<String>();
// ...

HashMap<String, ArrayList<String>> map = new HashMap<>();

It's better to use interface types in declarations, like this:

List<String> words = new ArrayList<>();
// ...

Map<String, List<String>> map = new HashMap<>();

And on the right-hand side, use the diamond operator <> when possible.

Use try-with-resources when working with resources

Instead of this:

Scanner s = new Scanner(new File("bg.txt"));

ArrayList<String> words = new ArrayList<String>();
while (s.hasNext()) {
    words.add(s.next());
}

// much much later...
s.close();

Write like this:

List<String> words = new ArrayList<>();
try (Scanner s = new Scanner(new File("bg.txt"))) {
    while (s.hasNext()) {
        words.add(s.next());
    }
}

Notice that s.close() is no longer necessary. That also means you cannot "forget" to close a resource manually.

You can read more about this here: https://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html