If you’re using Apache Commons Lang, then you can use one of the variations of ConcurrentInitializer like LazyInitializer.
Example:
ConcurrentInitializer<Foo> lazyInitializer = new LazyInitializer<Foo>() {
@Override
protected Foo initialize() throws ConcurrentException {
return new Foo();
}
};
You can now safely get Foo (gets initialized only once):
Foo instance = lazyInitializer.get();
If you’re using Google’s Guava:
Supplier<Foo> fooSupplier = Suppliers.memoize(new Supplier<Foo>() {
public Foo get() {
return new Foo();
}
});
Then call it by Foo f = fooSupplier.get();
From Suppliers.memoize javadoc:
Returns a supplier which caches the instance retrieved during the first call to get() and returns that value on subsequent calls to get(). The returned supplier is thread-safe. The delegate’s get() method will be invoked at most once. If delegate is an instance created by an earlier call to memoize, it is returned directly.