ログインおよび登録機能を実装する際、ユーザー情報はローカルデータベースに保存し、認証処理はそのデータベースから行う必要がある。以下では、AndroidでSQLiteを活用してユーザー登録とログインを実現する方法を示す。

DatabaseHelper.java

package com.example.fuxing.service;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

public class DatabaseHelper extends SQLiteOpenHelper {
    private static final String DATABASE_NAME = "user.db";
    private static final int DATABASE_VERSION = 1;

    public DatabaseHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        String createTableQuery = "CREATE TABLE user (" +
                "id INTEGER PRIMARY KEY AUTOINCREMENT, " +
                "username TEXT, " +
                "password TEXT, " +
                "email TEXT, " +
                "phonenumber TEXT)";
        db.execSQL(createTableQuery);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // バージョンアップ時の処理（今回は未使用）
    }
}

UserService.java

package com.example.fuxing.service;

import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;

import com.example.fuxing.User;

public class UserService {
    private final DatabaseHelper dbHelper;

    public UserService(Context context) {
        this.dbHelper = new DatabaseHelper(context);
    }

    public boolean authenticate(String username, String password) {
        SQLiteDatabase db = dbHelper.getReadableDatabase();
        String query = "SELECT 1 FROM user WHERE username = ? AND password = ?";
        try (Cursor cursor = db.rawQuery(query, new String[]{username, password})) {
            return cursor.moveToFirst();
        }
    }

    public boolean createUser(User user) {
        SQLiteDatabase db = dbHelper.getWritableDatabase();
        String insertQuery = "INSERT INTO user(username, password, email, phonenumber) VALUES (?, ?, ?, ?)";
        db.execSQL(insertQuery, new Object[]{
                user.getUsername(),
                user.getPassword(),
                user.getEmail(),
                user.getPhonenumber()
        });
        return true;
    }
}

User.java

package com.example.fuxing;

import java.io.Serializable;

public class User implements Serializable {
    private int id;
    private String username;
    private String password;
    private String email;
    private String phoneNumber;

    public User() {}

    public User(String username, String password, String email, String phoneNumber) {
        this.username = username;
        this.password = password;
        this.email = email;
        this.phoneNumber = phoneNumber;
    }

    // GetterとSetterメソッド
    public int getId() { return id; }
    public void setId(int id) { this.id = id; }

    public String getUsername() { return username; }
    public void setUsername(String username) { this.username = username; }

    public String getPassword() { return password; }
    public void setPassword(String password) { this.password = password; }

    public String getEmail() { return email; }
    public void setEmail(String email) { this.email = email; }

    public String getPhoneNumber() { return phoneNumber; }
    public void setPhoneNumber(String phoneNumber) { this.phoneNumber = phoneNumber; }

    @Override
    public String toString() {
        return "User{id=" + id +
                ", username='" + username + '\'' +
                ", password='" + password + '\'' +
                ", email='" + email + '\'' +
                ", phoneNumber='" + phoneNumber + "'}";
    }
}