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