在Android中连接数据库以存储用户的登录/注册详细信息，可以使用SQLite数据库来实现。以下是一个简单的示例代码：

首先，在Android的项目中创建一个DatabaseHelper类，用于创建和管理数据库：

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;

    private static final String CREATE_TABLE_USERS = "CREATE TABLE users (id INTEGER PRIMARY KEY AUTOINCREMENT, username TEXT, password TEXT)";

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

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(CREATE_TABLE_USERS);
    }

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

接下来，在你的注册/登录Activity中使用DatabaseHelper类来处理数据库操作：

import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {
    private EditText usernameEditText, passwordEditText;
    private Button registerButton, loginButton;

    private DatabaseHelper databaseHelper;

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

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

        databaseHelper = new DatabaseHelper(this);

        registerButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String username = usernameEditText.getText().toString();
                String password = passwordEditText.getText().toString();

                if (username.isEmpty() || password.isEmpty()) {
                    Toast.makeText(MainActivity.this, "Please enter username and password", Toast.LENGTH_SHORT).show();
                } else {
                    SQLiteDatabase db = databaseHelper.getWritableDatabase();

                    ContentValues values = new ContentValues();
                    values.put("username", username);
                    values.put("password", password);

                    long result = db.insert("users", null, values);
                    if (result == -1) {
                        Toast.makeText(MainActivity.this, "Failed to register", Toast.LENGTH_SHORT).show();
                    } else {
                        Toast.makeText(MainActivity.this, "Registered successfully", Toast.LENGTH_SHORT).show();
                    }

                    db.close();
                }
            }
        });

        loginButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String username = usernameEditText.getText().toString();
                String password = passwordEditText.getText().toString();

                if (username.isEmpty() || password.isEmpty()) {
                    Toast.makeText(MainActivity.this, "Please enter username and password", Toast.LENGTH_SHORT).show();
                } else {
                    SQLiteDatabase db = databaseHelper.getReadableDatabase();

                    String[] projection = {"username"};
                    String selection = "username = ? AND password = ?";
                    String[] selectionArgs = {username, password};

                    Cursor cursor = db.query("users", projection, selection, selectionArgs, null, null, null);
                    if (cursor.getCount() > 0) {
                        Toast.makeText(MainActivity.this, "Login successful", Toast.LENGTH_SHORT).show();
                    } else {
                        Toast.makeText(MainActivity.this, "Invalid username or password", Toast.LENGTH_SHORT).show();
                    }

                    cursor.close();
                    db.close();
                }
            }
        });
    }
}

以上代码使用了一个DatabaseHelper类来创建和管理数据库。在注册按钮的点击事件中，将用户的用户名和密码插入到名为"users"的表中。在登录按钮的点击事件中，使用查询操作来验证用户名和密码。

注意：这只是一个简单的示例代码，实际应用中需要进行更多的错误处理和安全措施。