3 ways to implement Java Singleton

1. Instantiate by static member field

 Public classElvis {/*** Invoke private constructor instantiation object by final static member field*/     Public Static FinalElvis INSTANCE =NewElvis (); /*** Private constructors to prevent instantiation outside of the class*/    PrivateElvis () {} Public voidleavethebuilding () {System.out.println ("Leave The building ..."); }     Public Static voidMain (string[] args) {Elvis.INSTANCE.leaveTheBuilding (); }}

2, through the public static factory method

 Public classElvis {/*** Set the static member field to private*/    Private Static FinalElvis INSTANCE =NewElvis (); /*** Private constructors to prevent instantiation outside of the class*/    PrivateElvis () {}/*** Export a single instance through the public static factory method *@returnSingleton Instances*/     PublicElvis getinstance () {returnINSTANCE; }     Public voidleavethebuilding () {System.out.println ("Leave The building ..."); }     Public Static voidMain (string[] args) {Elvis.INSTANCE.leaveTheBuilding (); }}

3, through enumeration to return, this way is more concise, free to provide a serialization mechanism, absolutely prevent multiple instantiation, even in the face of multiple serialization and fan serialization attacks. Although this approach has not been widely adopted, this approach has become the best way to implement Singleton.

 Public classElvis {/*** Set the static member field to private*/    Private Static FinalElvis INSTANCE =NewElvis (); /*** Private constructors to prevent instantiation outside of the class*/    PrivateElvis () {}/*** Implemented by an enumeration type that contains a single element, as recommended (from the Java 1.5 release)*/     Public enumElvis1 {INSTANCE;  Public voidleavethebuilding () {System.out.println ("Leave The building ..."); }    }     Public Static voidMain (string[] args) {Elvis1.INSTANCE.leaveTheBuilding (); }}

3 ways to implement Java Singleton