用安卓java实现一个用户登录注册的SQL数据库程序

好的，下面是一个简单的安卓Java程序，实现用户登录和注册的SQL数据库操作。

首先，需要在安卓项目中添加SQLiteDatabase的依赖库，可以在build.gradle文件中添加以下代码：

dependencies {
    implementation 'com.android.support:support-sqlite:28.0.0'
}

接着，在MainActivity类中定义一个SQLiteOpenHelper类来创建和管理数据库。这里我们创建一个名为"UserDB"的数据库，其中包含一个名为"users"的表，用于存储用户信息。

public class UserDBHelper extends SQLiteOpenHelper {

    private static final String DATABASE_NAME = "UserDB";
    private static final int DATABASE_VERSION = 1;
    private static final String TABLE_NAME = "users";
    private static final String COLUMN_ID = "id";
    private static final String COLUMN_USERNAME = "username";
    private static final String COLUMN_PASSWORD = "password";

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

    @Override
    public void onCreate(SQLiteDatabase db) {
        String CREATE_TABLE = "CREATE TABLE " + TABLE_NAME + "("
                + COLUMN_ID + " INTEGER PRIMARY KEY AUTOINCREMENT,"
                + COLUMN_USERNAME + " TEXT,"
                + COLUMN_PASSWORD + " TEXT" + ")";
        db.execSQL(CREATE_TABLE);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
        onCreate(db);
    }
}

接着，在MainActivity中，定义一个User类来表示用户信息，包含用户名和密码属性。

public class User {
    private int id;
    private String username;
    private String password;

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

    // getter and setter methods
}

接下来，实现注册和登录功能。在注册功能中，将新用户的用户名和密码插入到数据库中；在登录功能中，查询数据库中是否存在相应的用户名和密码。

public class MainActivity extends AppCompatActivity {

    private EditText usernameEditText;
    private EditText passwordEditText;

    private UserDBHelper dbHelper;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        dbHelper = new UserDBHelper(this);

        usernameEditText = findViewById(R.id.usernameEditText);
        passwordEditText = findViewById(R.id.passwordEditText);

        Button registerButton = findViewById(R.id.registerButton);
        registerButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String username = usernameEditText.getText().toString();
                String password = passwordEditText.getText().toString();
                User user = new User(username, password);
                registerUser(user);
            }
        });

        Button loginButton = findViewById(R.id.loginButton);
        loginButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String username = usernameEditText.getText().toString();
                String password = passwordEditText.getText().toString();
                User user = new User(username, password);
                if (authenticateUser(user)) {
                    // login success
                } else {
                    // login failed
                }
            }
        });
    }

    private void registerUser(User user) {
        SQLiteDatabase db = dbHelper.getWritableDatabase();

        ContentValues values = new ContentValues();
        values.put(UserDBHelper.COLUMN_USERNAME, user.getUsername());
        values.put(UserDBHelper.COLUMN_PASSWORD, user.getPassword());

        db.insert(UserDBHelper.TABLE_NAME, null, values);
        db.close();
    }

    private boolean authenticateUser(User user) {
        SQLiteDatabase db = dbHelper.getReadableDatabase();

        String[] projection = {
                UserDBHelper.COLUMN_ID
        };

        String selection = UserDBHelper.COLUMN_USERNAME + " = ? and " + UserDBHelper.COLUMN_PASSWORD + " = ?";
        String[] selectionArgs = { user.getUsername(), user.getPassword() };

        Cursor cursor = db.query(
                UserDBHelper.TABLE_NAME,
                projection,
                selection,
                selectionArgs,
                null,
                null,
                null
        );

        boolean result = cursor.moveToFirst();
        cursor.close();
        db.close();

        return result;
    }
}

以上就是一个简单的安卓Java程序，实现用户登录和注册的SQL数据库操作。需要注意的是，这只是一个简单的示例，实际开发中需要根据具体需求进行修改和完善。