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      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      */
     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      */
     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      */
     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      */
     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      */
     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      */
    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