What reasons make the Singleton class considered bad practice in development?

The Singleton class is considered a bad practice for several reasons:

1. Global state: Singleton is essentially a global object, which complicates tracking changes and leads to undesirable side effects.

2. Testing difficulties: Due to the global state, it is difficult to isolate tests, as Singleton maintains state between tests.

3. Violation of OOP principles: Singleton violates the single responsibility principle and can create hidden dependencies.

4. Multithreading issues: If Singleton is not implemented correctly, race conditions can occur.

5. Extension complexity: Singleton makes inheritance and behavior modification difficult.

Instead of Singleton, dependency injection or explicitly creating objects where needed is often recommended.