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java/org/apache/tomcat/util/digester/ArrayStack.java

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+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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 org.apache.tomcat.util.digester;
+
+import java.util.ArrayList;
+import java.util.EmptyStackException;
+
+/**
+ * <p>Imported copy of the <code>ArrayStack</code> class from
+ * Commons Collections, which was the only direct dependency from Digester.</p>
+ *
+ * <p><strong>WARNNG</strong> - This class is public solely to allow it to be
+ * used from subpackages of <code>org.apache.commons.digester</code>.
+ * It should not be considered part of the public API of Commons Digester.
+ * If you want to use such a class yourself, you should use the one from
+ * Commons Collections directly.</p>
+ *
+ * <p>An implementation of the {@link java.util.Stack} API that is based on an
+ * <code>ArrayList</code> instead of a <code>Vector</code>, so it is not
+ * synchronized to protect against multi-threaded access.  The implementation
+ * is therefore operates faster in environments where you do not need to
+ * worry about multiple thread contention.</p>
+ *
+ * <p>Unlike <code>Stack</code>, <code>ArrayStack</code> accepts null entries.
+ * </p>
+ *
+ * @param <E> Type of object in this stack
+ *
+ * @see java.util.Stack
+ * @since Digester 1.6 (from Commons Collections 1.0)
+ */
+public class ArrayStack<E> extends ArrayList<E> {
+
+    /** Ensure serialization compatibility */
+    private static final long serialVersionUID = 2130079159931574599L;
+
+    /**
+     * Constructs a new empty <code>ArrayStack</code>. The initial size
+     * is controlled by <code>ArrayList</code> and is currently 10.
+     */
+    public ArrayStack() {
+        super();
+    }
+
+    /**
+     * Constructs a new empty <code>ArrayStack</code> with an initial size.
+     *
+     * @param initialSize  the initial size to use
+     * @throws IllegalArgumentException  if the specified initial size
+     *  is negative
+     */
+    public ArrayStack(int initialSize) {
+        super(initialSize);
+    }
+
+    /**
+     * Return <code>true</code> if this stack is currently empty.
+     * <p>
+     * This method exists for compatibility with <code>java.util.Stack</code>.
+     * New users of this class should use <code>isEmpty</code> instead.
+     *
+     * @return true if the stack is currently empty
+     */
+    public boolean empty() {
+        return isEmpty();
+    }
+
+    /**
+     * Returns the top item off of this stack without removing it.
+     *
+     * @return the top item on the stack
+     * @throws EmptyStackException  if the stack is empty
+     */
+    public E peek() throws EmptyStackException {
+        int n = size();
+        if (n <= 0) {
+            throw new EmptyStackException();
+        } else {
+            return get(n - 1);
+        }
+    }
+
+    /**
+     * Returns the n'th item down (zero-relative) from the top of this
+     * stack without removing it.
+     *
+     * @param n  the number of items down to go
+     * @return the n'th item on the stack, zero relative
+     * @throws EmptyStackException  if there are not enough items on the
+     *  stack to satisfy this request
+     */
+    public E peek(int n) throws EmptyStackException {
+        int m = (size() - n) - 1;
+        if (m < 0) {
+            throw new EmptyStackException();
+        } else {
+            return get(m);
+        }
+    }
+
+    /**
+     * Pops the top item off of this stack and return it.
+     *
+     * @return the top item on the stack
+     * @throws EmptyStackException  if the stack is empty
+     */
+    public E pop() throws EmptyStackException {
+        int n = size();
+        if (n <= 0) {
+            throw new EmptyStackException();
+        } else {
+            return remove(n - 1);
+        }
+    }
+
+    /**
+     * Pushes a new item onto the top of this stack. The pushed item is also
+     * returned. This is equivalent to calling <code>add</code>.
+     *
+     * @param item  the item to be added
+     * @return the item just pushed
+     */
+    public E push(E item) {
+        add(item);
+        return item;
+    }
+}