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package de.team33.patterns.lazy.narvi;
import de.team33.patterns.exceptional.dione.XSupplier;
import java.util.function.Supplier;
/**
* Implements a kind of supplier that provides a virtually fixed value.
* That value is only actually determined when it is accessed for the first time.
*
* This implementation ensures that the {@linkplain #init(XSupplier) originally defined initialization code}
* is called at most once, even if there is concurrent access from multiple threads, unless the
* initialization attempt causes an exception.
*
* Once the value is established, unnecessary effort to synchronize competing* read accesses is avoided.
*
* *Pure read accesses are of course not really competing.
*
* @see Lazy
*/
public class XLazy extends Mutual {
private XLazy(final XSupplier initial) {
super(initial::get);
}
/**
* Returns a new {@link XLazy} instance giving a {@link Supplier} that defines the intended initialization of the
* represented value.
*
* @param The result type of the initialisation code.
* @param The exception type that may occur within initialisation.
*/
public static XLazy init(final XSupplier initial) {
return new XLazy<>(initial);
}
/**
* Executes the {@linkplain #init(XSupplier) originally defined initialization code} once on the first call
* and returns its result on that and every subsequent call without executing the initialization code again.
* This method is thread safe.
*/
@Override
public final T get() throws X {
return super.get();
}
}