3, using private constructors or enumeration types to enhance the Singleton property __effective

Conclusions

Single-element enumeration types have become the best way to implement singleton singleton patterns

Common Singleton have two ways, the first:

public class Elvis {
    //is defined as final, immutable public
    static final Elvis INSTANCE = new Elvis ();

    Private Elvis () {
    } public

    void Leavethebuilding () {
        System.out.println ("Whoa baby, I ' outta here!");
    }

    //This code would normally appear outside the class!
    public static void Main (string[] args) {
        Elvis Elvis = elvis.instance;
        Elvis.leavethebuilding ();
    }

The second way:

public class Elvis {
    private static final Elvis INSTANCE = new Elvis ();

    Private Elvis () {
    }
    ///defined as static method public
    static Elvis getinstance () {return
        INSTANCE;
    }

    public void leavethebuilding () {
        System.out.println ("Whoa baby, I ' M outta here!");
    }

    This code would normally appear outside the class!
    public static void Main (string[] args) {
        Elvis Elvis = Elvis.getinstance ();
        Elvis.leavethebuilding ();
    }

let Singleton become serializable.

To create only one object for deserialization

public class Elvis {public
    static final Elvis INSTANCE = new Elvis ();

    Private Elvis () {
    } public

    void Leavethebuilding () {
        System.out.println ("Whoa baby, I ' outta here!");
    }

    private Object Readresolve () {//Return the one true Elvis and let the
        garbage collector
        //Take care of the Elvis impersonator.
        return INSTANCE;
    }

    This code would normally appear outside the class!
    public static void Main (string[] args) {
        Elvis Elvis = elvis.instance;
        Elvis.leavethebuilding ();
    }

using enumerations to implement a single case pattern

Provides a serialization mechanism for free, and absolutely prevents multiple instantiations

public enum Elvis {INSTANCE;
    public void leavethebuilding () {System.out.println ("Whoa baby, I ' M outta here!");
    }//This code would normally appear outside the class!
        public static void Main (string[] args) {Elvis Elvis = elvis.instance;
    Elvis.leavethebuilding (); }
}