Update #0 - First Release

sources/main/java/com/google/common/collect/AbstractSequentialIterator.java

@@ -0,0 +1,85 @@
+/*
+ * Copyright (C) 2010 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 java.util.NoSuchElementException;
+
+import javax.annotation.Nullable;
+
+import com.google.common.annotations.GwtCompatible;
+
+/**
+ * This class provides a skeletal implementation of the {@code Iterator}
+ * interface for sequences whose next element can always be derived from the
+ * previous element. Null elements are not supported, nor is the
+ * {@link #remove()} method.
+ *
+ * <p>
+ * Example:
+ * 
+ * <pre>
+ * {
+ * 	&#64;code
+ *
+ * 	Iterator<Integer> powersOfTwo = new AbstractSequentialIterator<Integer>(1) {
+ * 		protected Integer computeNext(Integer previous) {
+ * 			return (previous == 1 << 30) ? null : previous * 2;
+ * 		}
+ * 	};
+ * }
+ * </pre>
+ *
+ * @author Chris Povirk
+ * @since 12.0 (in Guava as {@code AbstractLinkedIterator} since 8.0)
+ */
+@GwtCompatible
+public abstract class AbstractSequentialIterator<T> extends UnmodifiableIterator<T> {
+	private T nextOrNull;
+
+	/**
+	 * Creates a new iterator with the given first element, or, if {@code
+	 * firstOrNull} is null, creates a new empty iterator.
+	 */
+	protected AbstractSequentialIterator(@Nullable T firstOrNull) {
+		this.nextOrNull = firstOrNull;
+	}
+
+	/**
+	 * Returns the element that follows {@code previous}, or returns {@code null} if
+	 * no elements remain. This method is invoked during each call to
+	 * {@link #next()} in order to compute the result of a <i>future</i> call to
+	 * {@code next()}.
+	 */
+	protected abstract T computeNext(T previous);
+
+	@Override
+	public final boolean hasNext() {
+		return nextOrNull != null;
+	}
+
+	@Override
+	public final T next() {
+		if (!hasNext()) {
+			throw new NoSuchElementException();
+		}
+		try {
+			return nextOrNull;
+		} finally {
+			nextOrNull = computeNext(nextOrNull);
+		}
+	}
+}