Reasons for Java Singleton mode (double check plus lock)

public class singleton{     private static Singleton instance = null;//Whether it is final is not important because it is possible to instantiate at most one time.     Private Singleton () {} public     static Singleton getinstance () {         if (instance = = null) {             //double check lock, The synchronization mechanism is enabled only for the first instantiation, which improves performance.             synchronized (singleton.class) {                 if (instance = = null) {                     instance = new Singleton ();}}         }         return instance;     }  

Double-check locks enable the synchronization mechanism to improve performance only when the first instantiation is made.

Reasons for Java Singleton mode (double check plus lock)