Lazy 的最终代码如何实现的？

public class Lazy< T> implements Supplier< T> {

private final Supplier< ? extends T> supplier;

private T value;

private Lazy(Supplier< ? extends T> supplier) { this.supplier = supplier; }

public static < T> Lazy< T> of(Supplier< ? extends T> supplier) { return new Lazy< >(supplier); }

public T get() { if (value == null) { T newValue = supplier.get();

if (newValue == null) { throw new IllegalStateException("Lazy value can not be null!"); }

value = newValue; }

return value; }

public < S> Lazy< S> map(Function< ? super T, ? extends S> function) { return Lazy.of(() -> function.apply(get())); }

public < S> Lazy< S> flatMap(Function< ? super T, Lazy< ? extends S>> function) { return Lazy.of(() -> function.apply(get()).get()); } }