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      1 /*
      2  * Copyright (C) 2008 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 
     17 package com.google.common.collect;
     18 
     19 import com.google.common.annotations.GwtCompatible;
     20 
     21 import java.util.Collection;
     22 import java.util.Comparator;
     23 import java.util.NoSuchElementException;
     24 import java.util.Set;
     25 
     26 import javax.annotation.Nullable;
     27 
     28 /**
     29  * An empty immutable sorted set.
     30  *
     31  * @author Jared Levy
     32  */
     33 @GwtCompatible(serializable = true, emulated = true)
     34 @SuppressWarnings("serial") // uses writeReplace(), not default serialization
     35 class EmptyImmutableSortedSet<E> extends ImmutableSortedSet<E> {
     36   EmptyImmutableSortedSet(Comparator<? super E> comparator) {
     37     super(comparator);
     38   }
     39 
     40   @Override
     41   public int size() {
     42     return 0;
     43   }
     44 
     45   @Override public boolean isEmpty() {
     46     return true;
     47   }
     48 
     49   @Override public boolean contains(Object target) {
     50     return false;
     51   }
     52 
     53   @Override public UnmodifiableIterator<E> iterator() {
     54     return Iterators.emptyIterator();
     55   }
     56 
     57   @Override boolean isPartialView() {
     58     return false;
     59   }
     60 
     61   private static final Object[] EMPTY_ARRAY = new Object[0];
     62 
     63   @Override public Object[] toArray() {
     64     return EMPTY_ARRAY;
     65   }
     66 
     67   @Override public <T> T[] toArray(T[] a) {
     68     if (a.length > 0) {
     69       a[0] = null;
     70     }
     71     return a;
     72   }
     73 
     74   @Override public boolean containsAll(Collection<?> targets) {
     75     return targets.isEmpty();
     76   }
     77 
     78   @Override public boolean equals(@Nullable Object object) {
     79     if (object instanceof Set) {
     80       Set<?> that = (Set<?>) object;
     81       return that.isEmpty();
     82     }
     83     return false;
     84   }
     85 
     86   @Override public int hashCode() {
     87     return 0;
     88   }
     89 
     90   @Override public String toString() {
     91     return "[]";
     92   }
     93 
     94   @Override
     95   public E first() {
     96     throw new NoSuchElementException();
     97   }
     98 
     99   @Override
    100   public E last() {
    101     throw new NoSuchElementException();
    102   }
    103 
    104   @Override
    105   ImmutableSortedSet<E> headSetImpl(E toElement, boolean inclusive) {
    106     return this;
    107   }
    108 
    109   @Override
    110   ImmutableSortedSet<E> subSetImpl(
    111       E fromElement, boolean fromInclusive, E toElement, boolean toInclusive) {
    112     return this;
    113   }
    114 
    115   @Override
    116   ImmutableSortedSet<E> tailSetImpl(E fromElement, boolean inclusive) {
    117     return this;
    118   }
    119 
    120   @Override int indexOf(@Nullable Object target) {
    121     return -1;
    122   }
    123 }
    124