在java中实现一个懒惰的供应商

Question

What is the right paradigm or utility class (can't seem to find a preexisting class) to implement a lazy supplier in Java?

I want to have something that handles the compute-once/cache-later behavior and allows me to specify the computation behavior independently. I know this probably has an error but it has the right semantics:

abstract public class LazySupplier<T> implements Supplier<T> 
{
    private volatile T t;
    final private Object lock = new Object();

    final public T get() {
        if (t == null)
        {
            synchronized(lock)
            {
                if (t == null)
                    t = compute();
            }
        }
        return t;
    }
    abstract protected T compute();
}

Answer 1

This is already implemented in Suppliers.memoize method.

public static <T> Supplier<T> memoize(Supplier<T> delegate)

Returns a supplier which caches the instance retrieved during the first call to get() and returns that value on subsequent calls to get(). See: memoization

The returned supplier is thread-safe. The delegate's get() method will be invoked at most once. The supplier's serialized form does not contain the cached value, which will be recalculated when get() is called on the reserialized instance.

If delegate is an instance created by an earlier call to memoize, it is returned directly.

Answer 2

Apache Commons Lang has a LazyInitializer .