Method: Memoize(Supplier)

1: /*
2: * *********************************************************************************************************************
3: *
4: * blueMarine II: Semantic Media Centre
5: * http://tidalwave.it/projects/bluemarine2
6: *
7: * Copyright (C) 2015 - 2021 by Tidalwave s.a.s. (http://tidalwave.it)
8: *
9: * *********************************************************************************************************************
10: *
11: * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
12: * the License. You may obtain a copy of the License at
13: *
14: * http://www.apache.org/licenses/LICENSE-2.0
15: *
16: * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
17: * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
18: * specific language governing permissions and limitations under the License.
19: *
20: * *********************************************************************************************************************
21: *
22: * git clone https://bitbucket.org/tidalwave/bluemarine2-src
23: * git clone https://github.com/tidalwave-it/bluemarine2-src
24: *
25: * *********************************************************************************************************************
26: */
27: package it.tidalwave.util;
28:
29: import javax.annotation.Nonnull;
30: import java.util.function.Supplier;
31: import static java.util.Objects.requireNonNull;
32:
33: /***********************************************************************************************************************
34: *
35: * @author Fabrizio Giudici
36: *
37: **********************************************************************************************************************/
38: public class Memoize<T>
39: {
40: private T value;
41:
42: private transient volatile boolean initialized;
43:
44: private transient volatile Supplier<T> supplier;
45:
46: public Memoize()
47: {
48: }
49:
50: public Memoize (@Nonnull final Supplier<T> supplier)
51: {
52: this.supplier = supplier;
53: }
54:
55: @Nonnull
56: public T get()
57: {
58: return get(requireNonNull(supplier, "get() can be used if the Supplier has been provided in the constructor"));
59: }
60:
61: @Nonnull
62: public T get (@Nonnull final Supplier<T> supplier)
63: {
64: if (!initialized) // double checked locking
65: {
66: synchronized (this)
67: {
68: if (!initialized)
69: {
70: value = supplier.get();
71: initialized = true;
72: }
73: }
74: }
75:
76: return value;
77: }
78: }