/*
* Copyright (C) 2007 The Guava Authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.google.common.collect;
import static com.google.common.base.Preconditions.checkElementIndex;
import static com.google.common.base.Preconditions.checkPositionIndex;
import static com.google.common.base.Preconditions.checkPositionIndexes;
import com.google.common.annotations.GwtCompatible;
import java.util.Collection;
import java.util.List;
import java.util.NoSuchElementException;
import javax.annotation.Nullable;
/**
* An empty immutable list.
*
* @author Kevin Bourrillion
*/
@GwtCompatible(serializable = true, emulated = true)
final class EmptyImmutableList extends ImmutableList<Object> {
static final EmptyImmutableList INSTANCE = new EmptyImmutableList();
static final UnmodifiableListIterator<Object> ITERATOR =
new UnmodifiableListIterator<Object>() {
@Override public boolean hasNext() {
return false;
}
@Override public boolean hasPrevious() {
return false;
}
@Override public Object next() {
throw new NoSuchElementException();
}
@Override public int nextIndex() {
return 0;
}
@Override public Object previous() {
throw new NoSuchElementException();
}
@Override public int previousIndex() {
return -1;
}
};
private EmptyImmutableList() {}
@Override
public int size() {
return 0;
}
@Override public boolean isEmpty() {
return true;
}
@Override boolean isPartialView() {
return false;
}
@Override public boolean contains(Object target) {
return false;
}
@Override public UnmodifiableIterator<Object> iterator() {
return Iterators.emptyIterator();
}
private static final Object[] EMPTY_ARRAY = new Object[0];
@Override public Object[] toArray() {
return EMPTY_ARRAY;
}
@Override public <T> T[] toArray(T[] a) {
if (a.length > 0) {
a[0] = null;
}
return a;
}
@Override
public Object get(int index) {
// guaranteed to fail, but at least we get a consistent message
checkElementIndex(index, 0);
throw new AssertionError("unreachable");
}
@Override public int indexOf(@Nullable Object target) {
return -1;
}
@Override public int lastIndexOf(@Nullable Object target) {
return -1;
}
@Override public ImmutableList<Object> subList(int fromIndex, int toIndex) {
checkPositionIndexes(fromIndex, toIndex, 0);
return this;
}
@Override public ImmutableList<Object> reverse() {
return this;
}
@Override public UnmodifiableListIterator<Object> listIterator(){
return ITERATOR;
}
@Override public UnmodifiableListIterator<Object> listIterator(int start) {
checkPositionIndex(start, 0);
return ITERATOR;
}
@Override public boolean containsAll(Collection<?> targets) {
return targets.isEmpty();
}
@Override public boolean equals(@Nullable Object object) {
if (object instanceof List) {
List<?> that = (List<?>) object;
return that.isEmpty();
}
return false;
}
@Override public int hashCode() {
return 1;
}
@Override public String toString() {
return "[]";
}
Object readResolve() {
return INSTANCE; // preserve singleton property
}
private static final long serialVersionUID = 0;
}
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