add some source code

notes/src/Stack.java

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+/*
+ * Copyright (c) 1994, 2010, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package java.util;
+
+/**
+ * The <code>Stack</code> class represents a last-in-first-out
+ * (LIFO) stack of objects. It extends class <tt>Vector</tt> with five
+ * operations that allow a vector to be treated as a stack. The usual
+ * <tt>push</tt> and <tt>pop</tt> operations are provided, as well as a
+ * method to <tt>peek</tt> at the top item on the stack, a method to test
+ * for whether the stack is <tt>empty</tt>, and a method to <tt>search</tt>
+ * the stack for an item and discover how far it is from the top.
+ * <p>
+ * When a stack is first created, it contains no items.
+ *
+ * <p>A more complete and consistent set of LIFO stack operations is
+ * provided by the {@link Deque} interface and its implementations, which
+ * should be used in preference to this class.  For example:
+ * <pre>   {@code
+ *   Deque<Integer> stack = new ArrayDeque<Integer>();}</pre>
+ *
+ * @author  Jonathan Payne
+ * @since   JDK1.0
+ */
+public
+class Stack<E> extends Vector<E> {
+    /**
+     * Creates an empty Stack.
+     */
+    public Stack() {
+    }
+
+    /**
+     * Pushes an item onto the top of this stack. This has exactly
+     * the same effect as:
+     * <blockquote><pre>
+     * addElement(item)</pre></blockquote>
+     *
+     * @param   item   the item to be pushed onto this stack.
+     * @return  the <code>item</code> argument.
+     * @see     java.util.Vector#addElement
+     */
+    public E push(E item) {
+        addElement(item);
+
+        return item;
+    }
+
+    /**
+     * Removes the object at the top of this stack and returns that
+     * object as the value of this function.
+     *
+     * @return  The object at the top of this stack (the last item
+     *          of the <tt>Vector</tt> object).
+     * @throws  EmptyStackException  if this stack is empty.
+     */
+    public synchronized E pop() {
+        E       obj;
+        int     len = size();
+
+        obj = peek();
+        removeElementAt(len - 1);
+
+        return obj;
+    }
+
+    /**
+     * Looks at the object at the top of this stack without removing it
+     * from the stack.
+     *
+     * @return  the object at the top of this stack (the last item
+     *          of the <tt>Vector</tt> object).
+     * @throws  EmptyStackException  if this stack is empty.
+     */
+    public synchronized E peek() {
+        int     len = size();
+
+        if (len == 0)
+            throw new EmptyStackException();
+        return elementAt(len - 1);
+    }
+
+    /**
+     * Tests if this stack is empty.
+     *
+     * @return  <code>true</code> if and only if this stack contains
+     *          no items; <code>false</code> otherwise.
+     */
+    public boolean empty() {
+        return size() == 0;
+    }
+
+    /**
+     * Returns the 1-based position where an object is on this stack.
+     * If the object <tt>o</tt> occurs as an item in this stack, this
+     * method returns the distance from the top of the stack of the
+     * occurrence nearest the top of the stack; the topmost item on the
+     * stack is considered to be at distance <tt>1</tt>. The <tt>equals</tt>
+     * method is used to compare <tt>o</tt> to the
+     * items in this stack.
+     *
+     * @param   o   the desired object.
+     * @return  the 1-based position from the top of the stack where
+     *          the object is located; the return value <code>-1</code>
+     *          indicates that the object is not on the stack.
+     */
+    public synchronized int search(Object o) {
+        int i = lastIndexOf(o);
+
+        if (i >= 0) {
+            return size() - i;
+        }
+        return -1;
+    }
+
+    /** use serialVersionUID from JDK 1.0.2 for interoperability */
+    private static final long serialVersionUID = 1224463164541339165L;
+}