How to make singleton class thread safe, what is volatile?

Question

Accepted Answer

To make a singleton class thread safe, use synchronized keyword or double-checked locking. Volatile keyword ensures visibility of changes across threads.

Use synchronized keyword to ensure only one thread can access the instance at a time
Use double-checked locking to avoid unnecessary synchronization
Declare the instance variable as volatile to ensure visibility of changes across threads
Example: public static synchronized Singleton getInstance() { if (instance == null) { instance = new Singleton(); } return instance; }
Example: public static Singleton getInstance() { if (instance == null) { synchronized (Singleton.class) { if (instance == null) { instance = new Singleton(); } } } return instance; }
Example: private volatile static Singleton instance;

How to make singleton class thread safe, what is volatile?

Top UST Senior Systems Analyst and Technical Lead interview questions & answers