【源代码】java.util.Stack & Queue

这里给出java.util.Stack和java.util.Queue的源代码。

Stack

栈容器的内容很简洁，声明如下：

public class Stack<T> extends Vector<T>

继承自Vector容器，构造函数为空。

然后定义两个基本操作Push和Pop：

  88:   public T push(T item)  89:   {  94:     addElement(item);  95:     return item;  96:   } 105:   public synchronized T pop() 106:   { 107:     if (elementCount == 0) 108:       throw new EmptyStackException(); 109:  110:     modCount++; 111:     T obj = elementData[--elementCount]; 114:     elementData[elementCount] = null; 115:     return obj; 116:   }

然后是获取栈顶对象的方法：

 124:   public synchronized T peek() 125:   { 126:     if (elementCount == 0) 127:       throw new EmptyStackException(); 128:  129:     return elementData[elementCount - 1]; 130:   }

检查是否为空的方法：

 137:   public synchronized boolean empty() 138:   { 139:     return elementCount == 0; 140:   }

最后定义一个搜索元素的方法：

 151:   public synchronized int search(Object o) 152:   { 153:     int i = elementCount; 154:     while (--i >= 0) 155:       if (equals(o, elementData[i])) 156:         return elementCount - i; 157:     return -1; 158:   }

其他就继承了所有Vector容器方法。

这里给出Stack容器源代码：

源代码来源：http://developer.classpath.org/doc/java/util/Stack-source.html

   1: /* Stack.java - Class that provides a Last In First Out (LIFO)   2:    datatype, known more commonly as a Stack   3:    Copyright (C) 1998, 1999, 2001, 2004, 2005   4:    Free Software Foundation, Inc.   5:    6: This file is part of GNU Classpath.   7:    8: GNU Classpath is free software; you can redistribute it and/or modify   9: it under the terms of the GNU General Public License as published by  10: the Free Software Foundation; either version 2, or (at your option)  11: any later version.  12:   13: GNU Classpath is distributed in the hope that it will be useful, but  14: WITHOUT ANY WARRANTY; without even the implied warranty of  15: MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU  16: General Public License for more details.  17:   18: You should have received a copy of the GNU General Public License  19: along with GNU Classpath; see the file COPYING.  If not, write to the  20: Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  21: 02110-1301 USA.  22:   23: Linking this library statically or dynamically with other modules is  24: making a combined work based on this library.  Thus, the terms and  25: conditions of the GNU General Public License cover the whole  26: combination.  27:   28: As a special exception, the copyright holders of this library give you  29: permission to link this library with independent modules to produce an  30: executable, regardless of the license terms of these independent  31: modules, and to copy and distribute the resulting executable under  32: terms of your choice, provided that you also meet, for each linked  33: independent module, the terms and conditions of the license of that  34: module.  An independent module is a module which is not derived from  35: or based on this library.  If you modify this library, you may extend  36: this exception to your version of the library, but you are not  37: obligated to do so.  If you do not wish to do so, delete this  38: exception statement from your version. */  39:   40:   41: package java.util;  42:   43: /* Written using "Java Class Libraries", 2nd edition, ISBN 0-201-31002-3  44:  * "The Java Language Specification", ISBN 0-201-63451-1  45:  * plus online API docs for JDK 1.2 beta from http://www.javasoft.com.  46:  * Status:  Believed complete and correct  47:   48: /**  49:  * Stack provides a Last In First Out (LIFO) data type, commonly known  50:  * as a Stack.  Stack itself extends Vector and provides the additional  51:  * methods for stack manipulation (push, pop, peek). You can also seek for  52:  * the 1-based position of an element on the stack.  53:  *  54:  * @author Warren Levy ([e-mail])  55:  * @author Eric Blake ([e-mail])  56:  * @see List  57:  * @see AbstractList  58:  * @see LinkedList  59:  * @since 1.0  60:  * @status updated to 1.4  61:  */  62: public class Stack<T> extends Vector<T>  63: {  64:   // We could use Vector methods internally for the following methods,  65:   // but have used Vector fields directly for efficiency (i.e. this  66:   // often reduces out duplicate bounds checking).  67:   68:   /**  69:    * Compatible with JDK 1.0+.  70:    */  71:   private static final long serialVersionUID = 1224463164541339165L;  72:   73:   /**  74:    * This constructor creates a new Stack, initially empty  75:    */  76:   public Stack()  77:   {  78:   }  79:   80:   /**  81:    * Pushes an Object onto the top of the stack.  This method is effectively  82:    * the same as addElement(item).  83:    *  84:    * @param item the Object to push onto the stack  85:    * @return the Object pushed onto the stack  86:    * @see Vector#addElement(Object)  87:    */  88:   public T push(T item)  89:   {  90:     // When growing the Stack, use the Vector routines in case more  91:     // memory is needed.  92:     // Note: spec indicates that this method *always* returns obj passed in!  93:   94:     addElement(item);  95:     return item;  96:   }  97:   98:   /**  99:    * Pops an item from the stack and returns it.  The item popped is 100:    * removed from the Stack. 101:    * 102:    * @return the Object popped from the stack 103:    * @throws EmptyStackException if the stack is empty 104:    */ 105:   public synchronized T pop() 106:   { 107:     if (elementCount == 0) 108:       throw new EmptyStackException(); 109:  110:     modCount++; 111:     T obj = elementData[--elementCount]; 112:  113:     // Set topmost element to null to assist the gc in cleanup. 114:     elementData[elementCount] = null; 115:     return obj; 116:   } 117:  118:   /** 119:    * Returns the top Object on the stack without removing it. 120:    * 121:    * @return the top Object on the stack 122:    * @throws EmptyStackException if the stack is empty 123:    */ 124:   public synchronized T peek() 125:   { 126:     if (elementCount == 0) 127:       throw new EmptyStackException(); 128:  129:     return elementData[elementCount - 1]; 130:   } 131:  132:   /** 133:    * Tests if the stack is empty. 134:    * 135:    * @return true if the stack contains no items, false otherwise 136:    */ 137:   public synchronized boolean empty() 138:   { 139:     return elementCount == 0; 140:   } 141:  142:   /** 143:    * Returns the position of an Object on the stack, with the top 144:    * most Object being at position 1, and each Object deeper in the 145:    * stack at depth + 1. 146:    * 147:    * @param o The object to search for 148:    * @return The 1 based depth of the Object, or -1 if the Object 149:    *         is not on the stack 150:    */ 151:   public synchronized int search(Object o) 152:   { 153:     int i = elementCount; 154:     while (--i >= 0) 155:       if (equals(o, elementData[i])) 156:         return elementCount - i; 157:     return -1; 158:   } 159: }

Queue

队列容器作为接口形式存在，定义如下

public interface Queue<E> extends Collection<E>

继承自Collection容器，接口方法定义如下：

boolean add(E e);boolean offer(E e);E remove();E poll();E element();E peek();

对于队列接口，这里有一个常见的实现LinkedList，所以可以有如下代码来将链表容器当做队列容器来使用：

Queue queue = new LinkedList<String>();queue.add("First");queue.add("Second");queue.add("Third");System.out.println(queue.remove());System.out.println(queue.remove());System.out.println(queue.remove());System.out.println(queue.size());

添加之后直接使用remove()方法可以以队列的方式来推出元素。这也是为什么LinkedList容器提供removeFirst() removeLast remove(int index)和remove(Object o)等不同移除对象的方法的原因。

需要了解LinkedList容器源代码可以参见我的博文《【源代码】java.util.LinkedList》