Present.java revision 3c77433663281544363151bf284b0240dfd22a42 
1/*
2 * Copyright (C) 2011 The Guava Authors
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package com.google.common.base;
18
19import static com.google.common.base.Preconditions.checkNotNull;
20
21import com.google.common.annotations.GwtCompatible;
22
23import java.util.Collections;
24import java.util.Set;
25
26import javax.annotation.Nullable;
27
28/**
29 * Implementation of an {@link Optional} containing a reference.
30 */
31@GwtCompatible
32final class Present<T> extends Optional<T> {
33  private final T reference;
34
35  Present(T reference) {
36    this.reference = reference;
37  }
38
39  @Override public boolean isPresent() {
40    return true;
41  }
42
43  @Override public T get() {
44    return reference;
45  }
46
47  @Override public T or(T defaultValue) {
48    checkNotNull(defaultValue, "use Optional.orNull() instead of Optional.or(null)");
49    return reference;
50  }
51
52  @Override public Optional<T> or(Optional<? extends T> secondChoice) {
53    checkNotNull(secondChoice);
54    return this;
55  }
56
57  @Override public T or(Supplier<? extends T> supplier) {
58    checkNotNull(supplier);
59    return reference;
60  }
61
62  @Override public T orNull() {
63    return reference;
64  }
65
66  @Override public Set<T> asSet() {
67    return Collections.singleton(reference);
68  }
69
70  @Override public <V> Optional<V> transform(Function<? super T, V> function) {
71    return new Present<V>(checkNotNull(function.apply(reference),
72        "the Function passed to Optional.transform() must not return null."));
73  }
74
75  @Override public boolean equals(@Nullable Object object) {
76    if (object instanceof Present) {
77      Present<?> other = (Present<?>) object;
78      return reference.equals(other.reference);
79    }
80    return false;
81  }
82
83  @Override public int hashCode() {
84    return 0x598df91c + reference.hashCode();
85  }
86
87  @Override public String toString() {
88    return "Optional.of(" + reference + ")";
89  }
90
91  private static final long serialVersionUID = 0;
92}
93