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9.1.1 数组列表
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9.1.1 数组列表
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<div id="text"> <link href="css.css" rel="stylesheet" type="text/css" /><h3 style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 0cm; MARGIN-RIGHT: 0cm; FTEL: 8.15pt"><a ftel="_Toc507815073"><span lang="EN-US">9.1.1 </span></a><span style="FONT-FAMILY: 黑体">数组列表</span></h3>
<p class="MsoNormal"><a ftel="arraylists"><span style="FONT-FAMILY: 宋体">数组列表非常类似于数组，但数组列表是可以增大的，它由</span><span lang="EN-US">System.Collections.ArrayList</span></a><span style="FONT-FAMILY: 宋体">类来表示。</span></p>
<p class="MsoNormal"><span lang="EN-US">ArrayList</span><span style="FONT-FAMILY: 宋体">类与前面的</span><span lang="EN-US">StringBuilder</span><span style="FONT-FAMILY: 宋体">类也有一些相似之处。</span><span lang="EN-US">StringBuilder</span><span style="FONT-FAMILY: 宋体">类可以分配足够的存储单元来存储一定量的字符，允许在该空间中处理字符，</span><span lang="EN-US">ArrayList</span><span style="FONT-FAMILY: 宋体">类也是这样，有足够的存储单元来存储一定量的对象引用，这样，就可以高效地处理这些对象引用。如果试图给</span><span lang="EN-US">ArrayList</span><span style="FONT-FAMILY: 宋体">类添加的对象数超出了容量允许的范围，</span><span lang="EN-US">ArrayList</span><span style="FONT-FAMILY: 宋体">类的容量就会自动增大，新增的内存区域可以存储当前容量两倍的元素，并重新定位这些元素。</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">通过指定最初的容量就可以实例化数组列表。例如，假定创建一个</span><span lang="EN-US">Vector</span><span style="FONT-FAMILY: 宋体">列表：</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><a ftel="ArrayList1"><span lang="EN-US">ArrayList vectors = <span class="codeintext-PRODUCTION"><span style="FONT-FAMILY: 'Times New Roman'">new</span></span> ArrayList(20);</span></a></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">如果没有指定初始大小，则把该大小默认设置为</span><span lang="EN-US">16</span><span style="FONT-FAMILY: 宋体">。</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US">ArrayList vectors = <span class="codeintext-PRODUCTION"><span style="FONT-FAMILY: 'Times New Roman'">new</span></span> ArrayList(); // capacity of 16</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">使用</span><span lang="EN-US">Add()</span><span style="FONT-FAMILY: 宋体">方法可以添加元素：</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US">vectors.Add(new Vector(2,2,2));</span></p>
<p class="2" style="MARGIN-TOP: 0cm; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US">vectors.Add(new Vector(3,5,6));</span></p>
<p class="MsoNormal"><span lang="EN-US">ArrayList</span><span style="FONT-FAMILY: 宋体">把所有的元素都当作对象引用。因此可以在</span><span lang="EN-US">ArrayList</span><span style="FONT-FAMILY: 宋体">中存储任何想要存储的对象，但在访问对象时，需要把它们的数据类型转换回合适的数据类型：</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US">Vector element1 = (Vector)vectors[1];</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">这个示例还显示了</span><span lang="EN-US">ArrayList</span><span style="FONT-FAMILY: 宋体">定义的一个索引符，这样，就可以使用类似于数组的语法来访问其元素了。也可以把元素插入到</span><span lang="EN-US">ArrayList</span><span style="FONT-FAMILY: 宋体">中：</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US">vectors.Insert(1, new Vector(3,2,2)); // inserts at position 1</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">还可以重写</span><span lang="EN-US">Insert()</span><span style="FONT-FAMILY: 宋体">方法，如果给定一个</span><span lang="EN-US">ICollection</span><span style="FONT-FAMILY: 宋体">接口引用，就可以把一个集合中的所有元素插入到</span><span lang="EN-US">ArrayList</span><span style="FONT-FAMILY: 宋体">中。</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">可以删除元素：</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US">v</span><span class="MsoCommentReference"><span lang="EN-US" style="DISPLAY: none; FONT-SIZE: 8pt; LETTER-SPACING: -0.1pt">v</span></span><span lang="EN-US">ectors.RemoveAt(1); // removes object at position 1</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">也可以为另一个方法</span><span lang="EN-US">Remove()</span><span style="FONT-FAMILY: 宋体">提供对象引用，但这么做，花费的时间会比较长，因为</span><span lang="EN-US">ArrayList</span><span style="FONT-FAMILY: 宋体">要在数组中进行线性搜索，以查找对象。</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">注意添加和删除元素都会使后续的元素在内存中作相应的改变，即使不需要对整个</span><span lang="EN-US">ArrayList</span><span style="FONT-FAMILY: 宋体">重新分配内存，也是这样。</span></p>
<p class="MsoNormal" style="TEXT-ALIGN: left" align="left"><span style="FONT-FAMILY: 宋体">可以通过</span><span lang="EN-US">Capacity</span><span style="FONT-FAMILY: 宋体">属性修改或读取容量：</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US">vectors.Capacity = 30;</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">但要注意，修改容量会给整个</span><span lang="EN-US">ArrayList</span><span style="FONT-FAMILY: 宋体">重新分配新的内存块，其容量大小是所要求的容量大小。</span></p>
<p class="MsoNormal"><span lang="EN-US">ArrayList</span><span style="FONT-FAMILY: 宋体">中的元素个数可以通过</span><span lang="EN-US">Count</span><span style="FONT-FAMILY: 宋体">属性获得：</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US">int nVectors = Vectors.Count;</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">如果需要建立一个对象数组，但预先不指定该数组有多大，就可以使用数组列表。此时，可以在</span><span lang="EN-US">ArrayList</span><span style="FONT-FAMILY: 宋体">中构造一个数组，在完成后，如果确实需要把数据当作数组来处理，就再把</span><span lang="EN-US">ArrayList</span><span style="FONT-FAMILY: 宋体">复制到一个数组</span><span lang="EN-US">(</span><span style="FONT-FAMILY: 宋体">例如，把数组传递给一个带有数组参数的方法</span><span lang="EN-US">)</span><span style="FONT-FAMILY: 宋体">。</span><span lang="EN-US">ArrayList</span><span style="FONT-FAMILY: 宋体">和</span><span lang="EN-US"> Array</span><span style="FONT-FAMILY: 宋体">之间的关系在许多方面都类似于</span><span lang="EN-US">StringBuilder</span><span style="FONT-FAMILY: 宋体">和</span><span lang="EN-US">String</span><span style="FONT-FAMILY: 宋体">的关系。</span></p>
<p class="MsoNormal"><span style="FONT-FAMILY: 宋体">但与</span><span lang="EN-US">StringBuilder</span><span style="FONT-FAMILY: 宋体">类不同的是，没有把数组列表转换为数组的方法。必须使用一个循环，手工复制引用。但要注意，只能复制引用，不能复制对象，所以不会对性能产生大的影响：</span></p>
<p class="2" style="MARGIN-TOP: 8.15pt; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><a ftel="_Toc507815074"><span class="codeintext-PRODUCTION"><span lang="EN-US" style="FONT-FAMILY: 'Times New Roman'">// vectors is an ArrayList instance being used to store Vector instances</span></span></a></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span class="codeintext-PRODUCTION"><span lang="EN-US" style="FONT-FAMILY: 'Times New Roman'">Vector</span></span><span lang="EN-US"> [] vectorsArray = <span class="codeintext-PRODUCTION"><span style="FONT-FAMILY: 'Times New Roman'">new Vector</span></span>[vectors.Count];</span></p>
<p class="2" style="MARGIN-LEFT: 21.45pt; FTEL: 18.45pt"><span class="codeintext-PRODUCTION"><span lang="EN-US" style="FONT-FAMILY: 'Times New Roman'">for</span></span><span lang="EN-US"> (<span class="codeintext-PRODUCTION"><span style="FONT-FAMILY: 'Times New Roman'">int</span></span> i=0 ; i< vectors.Count ; i++)</span></p>
<p class="2" style="MARGIN-TOP: 0cm; MARGIN-LEFT: 21.45pt; MARGIN-RIGHT: 0cm; FTEL: 18.45pt"><span lang="EN-US"> vectorsArray[i] = (<span class="codeintext-PRODUCTION"><span style="FONT-FAMILY: 'Times New Roman'">Vector</span></span>)vectors [i];</span></p></div>
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