| /* |
| * 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 java.util; |
| |
| /** |
| * {@code Stack} is a Last-In/First-Out(LIFO) data structure which represents a |
| * stack of objects. It enables users to pop to and push from the stack, |
| * including null objects. There is no limit to the size of the stack. |
| */ |
| public class Stack<E> extends Vector<E> { |
| |
| private static final long serialVersionUID = 1224463164541339165L; |
| |
| /** |
| * Constructs a stack with the default size of {@code Vector}. |
| */ |
| public Stack() { |
| super(); |
| } |
| |
| /** |
| * Returns whether the stack is empty or not. |
| * |
| * @return {@code true} if the stack is empty, {@code false} otherwise. |
| */ |
| public boolean empty() { |
| return isEmpty(); |
| } |
| |
| /** |
| * Returns the element at the top of the stack without removing it. |
| * |
| * @return the element at the top of the stack. |
| * @throws EmptyStackException |
| * if the stack is empty. |
| * @see #pop |
| */ |
| @SuppressWarnings("unchecked") |
| public synchronized E peek() { |
| try { |
| return (E) elementData[elementCount - 1]; |
| } catch (IndexOutOfBoundsException e) { |
| throw new EmptyStackException(); |
| } |
| } |
| |
| /** |
| * Returns the element at the top of the stack and removes it. |
| * |
| * @return the element at the top of the stack. |
| * @throws EmptyStackException |
| * if the stack is empty. |
| * @see #peek |
| * @see #push |
| */ |
| @SuppressWarnings("unchecked") |
| public synchronized E pop() { |
| if (elementCount == 0) { |
| throw new EmptyStackException(); |
| } |
| final int index = --elementCount; |
| final E obj = (E) elementData[index]; |
| elementData[index] = null; |
| modCount++; |
| return obj; |
| } |
| |
| /** |
| * Pushes the specified object onto the top of the stack. |
| * |
| * @param object |
| * The object to be added on top of the stack. |
| * @return the object argument. |
| * @see #peek |
| * @see #pop |
| */ |
| public E push(E object) { |
| addElement(object); |
| return object; |
| } |
| |
| /** |
| * Returns the index of the first occurrence of the object, starting from |
| * the top of the stack. |
| * |
| * @return the index of the first occurrence of the object, assuming that |
| * the topmost object on the stack has a distance of one. |
| * @param o |
| * the object to be searched. |
| */ |
| public synchronized int search(Object o) { |
| final Object[] dumpArray = elementData; |
| final int size = elementCount; |
| if (o != null) { |
| for (int i = size - 1; i >= 0; i--) { |
| if (o.equals(dumpArray[i])) { |
| return size - i; |
| } |
| } |
| } else { |
| for (int i = size - 1; i >= 0; i--) { |
| if (dumpArray[i] == null) { |
| return size - i; |
| } |
| } |
| } |
| return -1; |
| } |
| } |