1 /*
2  * Copyright (C) 2007 The Android Open Source Project
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 
17 package com.google.android.collect;
18 
19 import android.util.ArraySet;
20 
21 import java.util.Collections;
22 import java.util.EnumSet;
23 import java.util.HashSet;
24 import java.util.SortedSet;
25 import java.util.TreeSet;
26 
27 /**
28  * Provides static methods for creating mutable {@code Set} instances easily and
29  * other static methods for working with Sets.
30  *
31  */
32 public class Sets {
33 
34     /**
35      * Creates an empty {@code HashSet} instance.
36      *
37      * <p><b>Note:</b> if {@code E} is an {@link Enum} type, use {@link
38      * EnumSet#noneOf} instead.
39      *
40      * <p><b>Note:</b> if you only need an <i>immutable</i> empty Set,
41      * use {@link Collections#emptySet} instead.
42      *
43      * @return a newly-created, initially-empty {@code HashSet}
44      */
newHashSet()45     public static <K> HashSet<K> newHashSet() {
46         return new HashSet<K>();
47     }
48 
49     /**
50      * Creates a {@code HashSet} instance containing the given elements.
51      *
52      * <p><b>Note:</b> due to a bug in javac 1.5.0_06, we cannot support the
53      * following:
54      *
55      * <p>{@code Set<Base> set = Sets.newHashSet(sub1, sub2);}
56      *
57      * <p>where {@code sub1} and {@code sub2} are references to subtypes of {@code
58      * Base}, not of {@code Base} itself. To get around this, you must use:
59      *
60      * <p>{@code Set<Base> set = Sets.<Base>newHashSet(sub1, sub2);}
61      *
62      * @param elements the elements that the set should contain
63      * @return a newly-created {@code HashSet} containing those elements (minus
64      *     duplicates)
65      */
newHashSet(E... elements)66     public static <E> HashSet<E> newHashSet(E... elements) {
67         int capacity = elements.length * 4 / 3 + 1;
68         HashSet<E> set = new HashSet<E>(capacity);
69         Collections.addAll(set, elements);
70         return set;
71     }
72 
73     /**
74      * Creates an empty {@code SortedSet} instance.
75      *
76      * @return a newly-created, initially-empty {@code SortedSet}.
77      */
newSortedSet()78     public static <E> SortedSet<E> newSortedSet() {
79         return new TreeSet<E>();
80     }
81 
82     /**
83      * Creates a {@code SortedSet} instance containing the given elements.
84      *
85      * @param elements the elements that the set should contain
86      * @return a newly-created {@code SortedSet} containing those elements (minus
87      *     duplicates)
88      */
newSortedSet(E... elements)89     public static <E> SortedSet<E> newSortedSet(E... elements) {
90         SortedSet<E> set = new TreeSet<E>();
91         Collections.addAll(set, elements);
92         return set;
93     }
94 
95     /**
96      * Creates a {@code ArraySet} instance.
97      */
newArraySet()98     public static <E> ArraySet<E> newArraySet() {
99         return new ArraySet<E>();
100     }
101 
102     /**
103      * Creates a {@code ArraySet} instance containing the given elements.
104      */
newArraySet(E... elements)105     public static <E> ArraySet<E> newArraySet(E... elements) {
106         int capacity = elements.length * 4 / 3 + 1;
107         ArraySet<E> set = new ArraySet<E>(capacity);
108         Collections.addAll(set, elements);
109         return set;
110     }
111 }
112