Efficient Implementation of Singleton Pattern in Java

Hello everyone! I'm a beginner Java developer and currently studying design patterns. I got to Singleton but got confused about the implementation.\n\nProblem: I need to create a class that is guaranteed to have only one instance throughout the entire application. I wrote a simple version with lazy initialization, but it doesn't work correctly in a multithreaded environment. Here's my code:\n\n```java\npublic class ConfigManager {\n private static ConfigManager instance;\n \n private ConfigManager() {}\n \n public static ConfigManager getInstance() {\n if (instance == null) {\n instance = new ConfigManager();\n }\n return instance;\n }\n}\n```\n\nWhen I run a test with multiple threads, sometimes multiple instances are created. I've read about synchronized, but I'm afraid it will