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      1 /*
      2  * Copyright (C) 2008 Google Inc.
      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)
     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   public int size() {
     41     return 0;
     42   }
     43 
     44   @Override public boolean isEmpty() {
     45     return true;
     46   }
     47 
     48   @Override public boolean contains(Object target) {
     49     return false;
     50   }
     51 
     52   @Override public UnmodifiableIterator<E> iterator() {
     53     return Iterators.emptyIterator();
     54   }
     55 
     56   private static final Object[] EMPTY_ARRAY = new Object[0];
     57 
     58   @Override public Object[] toArray() {
     59     return EMPTY_ARRAY;
     60   }
     61 
     62   @Override public <T> T[] toArray(T[] a) {
     63     if (a.length > 0) {
     64       a[0] = null;
     65     }
     66     return a;
     67   }
     68 
     69   @Override public boolean containsAll(Collection<?> targets) {
     70     return targets.isEmpty();
     71   }
     72 
     73   @Override public boolean equals(@Nullable Object object) {
     74     if (object instanceof Set) {
     75       Set<?> that = (Set<?>) object;
     76       return that.isEmpty();
     77     }
     78     return false;
     79   }
     80 
     81   @Override public int hashCode() {
     82     return 0;
     83   }
     84 
     85   @Override public String toString() {
     86     return "[]";
     87   }
     88 
     89   public E first() {
     90     throw new NoSuchElementException();
     91   }
     92 
     93   public E last() {
     94     throw new NoSuchElementException();
     95   }
     96 
     97   @Override ImmutableSortedSet<E> headSetImpl(E toElement) {
     98     return this;
     99   }
    100 
    101   @Override ImmutableSortedSet<E> subSetImpl(E fromElement, E toElement) {
    102     return this;
    103   }
    104 
    105   @Override ImmutableSortedSet<E> tailSetImpl(E fromElement) {
    106     return this;
    107   }
    108 
    109   @Override boolean hasPartialArray() {
    110     return false;
    111   }
    112 
    113   @Override int indexOf(Object target) {
    114     return -1;
    115   }
    116 }
    117