Singleton

  Below are the following cases which you can consider while implementing the singleton -
​
​                 Case 1 : If there is no memory constraint & initialization will not take much time.
​                               then go with eager initialization like -
                                            public static Singleton singleton = new Singleton();
​                               And make the constructor as private.
​                 Case 2 : If the properties of the singleton class can't be provided during
​                               construction then can try for Case 3 solution.
​                 Case 3 : If memory constraint is applicable & initialization takes time, then go with
​                               lazy initialization by providing one public static method that returns the
                               instance & once created then every time that instance will be returned by
                               that method.
​                Case 4 : If multithreaded environment is applicable & case 3 constraints are not
​                              present then use case 1 solution, it is best in such cases.
​                Case 5 : If multithreaded environment is applicable & case 3 constraints are also
​                              applicable then double checked locking concept can be used but also
​                              check this & this. And I think that using static/class variable should resolve
​                              other issues as pointed here.
​                 Case 6 : In multithreaded environment, if you are still eager to code your singleton
​                               class then look to override readResolve() & writeReplace() methods.
​                 Case 7 : If you are using jdk5 & above, then use enum directly without taking above
​                               pains.
​ And I think that there is no such thing called singleton across multiple JVMs.
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