Java文件加解密程序：如何移除加密密钥中的重复字符？

Hey there! Let's fix that duplicate character issue for your encryption key. I'll walk you through the implementation step by step, plus fix a couple of small typos in your existing code.

First, the Core Logic: Removing Duplicates #

There are two straightforward ways to strip duplicate characters from your key string. Both will preserve the original order of characters (which is critical for encryption consistency):

Method 1: Using StringBuilder with Index Check

This simple approach checks each character against the ones we've already added to a StringBuilder:

private static String removeDuplicates(String input) {
    StringBuilder uniqueChars = new StringBuilder();
    for (char c : input.toCharArray()) {
        // Only add the character if it hasn't been included before
        if (uniqueChars.indexOf(String.valueOf(c)) == -1) {
            uniqueChars.append(c);
        }
    }
    return uniqueChars.toString();
}

Method 2: Using HashSet (More Efficient)

For longer keys, this method is faster because HashSet checks for duplicates in constant time:

import java.util.HashSet;
import java.util.Set;

private static String removeDuplicates(String input) {
    Set<Character> seenChars = new HashSet<>();
    StringBuilder uniqueChars = new StringBuilder();
    for (char c : input.toCharArray()) {
        // HashSet.add() returns false if the character already exists
        if (seenChars.add(c)) {
            uniqueChars.append(c);
        }
    }
    return uniqueChars.toString();
}

Integrating This into Your Existing Code #

Here's your updated code with the duplicate removal logic added, plus fixes for typos (like System.ed → System.in and in.next() → console.next()):

import java.io.File;
import java.io.FileNotFoundException;
import java.io.PrintWriter;
import java.util.HashSet;
import java.util.Scanner;
import java.util.Set;

public class FileEncryptorDecryptor { // Renamed for clarity (feel free to change back)
    public static void main(String[] args) throws FileNotFoundException {
        System.out.print("Would you like to encrypt or decrypt. e/d: ");
        Scanner ed = new Scanner(System.in); // Fixed System.ed typo
        String eOrD = ed.next();

        if (eOrD.equals("e")) {
            Scanner console = new Scanner(System.in);
            System.out.print("Output File: ");
            String outputFileName = console.next();
            PrintWriter out = new PrintWriter(outputFileName);

            System.out.print("Please enter an encryption key: ");
            String keyWord = console.next(); // Fixed in.next() typo

            // Process the key to remove duplicates
            String processedKey = removeDuplicates(keyWord);
            System.out.println("Processed key (duplicates removed): " + processedKey);

            // Add your encryption logic here using processedKey
            // ...

            // Clean up resources
            out.close();
            console.close();
        }
        ed.close();
    }

    private static String removeDuplicates(String input) {
        Set<Character> seenChars = new HashSet<>();
        StringBuilder uniqueChars = new StringBuilder();
        for (char c : input.toCharArray()) {
            if (seenChars.add(c)) {
                uniqueChars.append(c);
            }
        }
        return uniqueChars.toString();
    }
}

Quick Notes: #

• The processedKey variable now holds your key with all duplicates stripped (e.g., "FEATHER" becomes "FEATHR").
• I renamed your class from Average to something more descriptive, but you can revert that if you prefer.
• Always close your Scanner and PrintWriter resources to avoid resource leaks.

内容的提问来源于stack exchange，提问作者MidnightMenace