Java: How to do double-checked-locking with an array element?

Please note that java implementation of double-checking is called "broken pattern" because it was proven as fail (for example see http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html ). To work around just use atomic operation. Follow is sample how to build thread safe singleton.

You could also consider using Suppliers. Memoize(Supplier delegate) from guava library.

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