001/*
002 * Copyright (C) 2008 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package com.google.common.collect;
018
019import com.google.common.annotations.GwtCompatible;
020import com.google.errorprone.annotations.DoNotCall;
021import java.util.Iterator;
022import org.jspecify.annotations.Nullable;
023
024/**
025 * An iterator that does not support {@link #remove}.
026 *
027 * <p>{@code UnmodifiableIterator} is used primarily in conjunction with implementations of {@link
028 * ImmutableCollection}, such as {@link ImmutableList}. You can, however, convert an existing
029 * iterator to an {@code UnmodifiableIterator} using {@link Iterators#unmodifiableIterator}.
030 *
031 * @author Jared Levy
032 * @since 2.0
033 */
034@GwtCompatible
035public abstract class UnmodifiableIterator<E extends @Nullable Object> implements Iterator<E> {
036  /** Constructor for use by subclasses. */
037  protected UnmodifiableIterator() {}
038
039  /**
040   * Guaranteed to throw an exception and leave the underlying data unmodified.
041   *
042   * @throws UnsupportedOperationException always
043   * @deprecated Unsupported operation.
044   */
045  @Deprecated
046  @Override
047  @DoNotCall("Always throws UnsupportedOperationException")
048  public final void remove() {
049    throw new UnsupportedOperationException();
050  }
051}