This is one of my school assignments and I just wanted to ask if there are some obvious mistakes or things I could maybe improve in this code.
Thank you for any suggestions.

```
import java.io.File;
import java.io.FileNotFoundException;
import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

public class App {
   public static void main(String[] args) {

    //Initialize and populate alphabet HashMap
    HashMap<Integer, Character> alphabet = new HashMap<Integer, Character>();
    alphabet.put(1, 'A');
    alphabet.put(2, 'B');
    alphabet.put(3, 'C');
    alphabet.put(4, 'D');
    alphabet.put(5, 'E');
    alphabet.put(6, 'F');
    alphabet.put(7, 'G');
    alphabet.put(8, 'H');
    alphabet.put(9, 'I');
    alphabet.put(10,'J');
    alphabet.put(11, 'K');
    alphabet.put(12, 'L');
    alphabet.put(13, 'M');
    alphabet.put(14, 'N');
    alphabet.put(15, 'O');
    alphabet.put(16, 'P');
    alphabet.put(17, 'Q');
    alphabet.put(18, 'R');
    alphabet.put(19, 'S');
    alphabet.put(20, 'T');
    alphabet.put(21, 'U');
    alphabet.put(22, 'V');
    alphabet.put(23, 'W');
    alphabet.put(24, 'X');
    alphabet.put(25, 'Y');
    alphabet.put(26, 'Z');

    try {
        //Load file
        File ciphertext = new File("ciphertext.txt");
        Scanner reader = new Scanner(ciphertext);

        //Input for key
        Scanner keyboard = new Scanner(System.in);
        System.out.println("Enter the key: ");
        int key = keyboard.nextInt();

        //Main while loop
        while (reader.hasNext()) {
            String data = reader.nextLine();
            String decrypted = "";

            //Loop through ciphertext.txt
            for (int i = 0; i < data.length(); i++) {

                //If current character is a space, append space to decrypted
                if (data.charAt(i) == ' '){
                    decrypted += ' ';
                }
                //For each element in alphabet
                for (Map.Entry<Integer, Character> entry : alphabet.entrySet()) {

                    //If entry == curr char in data (entry = one alphabet letter)
                    if (entry.getValue() == data.charAt(i)) {

                        //If entry + key is greater than 26
                        if (entry.getKey() + key > 26) {

                            //Total key - 26
                            decrypted += alphabet.get(entry.getKey() + key - 26);
                        } else {
                            decrypted += alphabet.get(entry.getKey() + key);
                        }

                    }
                }
            }
            System.out.println(decrypted);
        }
        //Close reader
        reader.close();

        //File not found exception
        } catch (FileNotFoundException e) {
        System.out.println("File not found");
        e.printStackTrace();
    }
}

```

}