java学习随笔--- 捣蛋vector，java随笔---vector
最近比较有时间啦，有时间搞下java,个人觉得学这门语言语法太多啦，不一一去学习啦，心血来潮，挂了个struct2的源代码，一入深似海啊，看得我天花缭乱，从最简单的开始吧
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 | <span> 1</span> <span>public</span> <span>static</span> <span>void</span><span> main(String[] args) {
</span><span> 2</span>
<span> 3</span> Vector v = <span>new</span> Vector(4<span>);
</span><span> 4</span>
<span> 5</span> <span>
</span><span> 6</span> <span>
<span> 7</span> v.add("Test0"<span>);
</span><span> 8</span> v.add("Test1"<span>);
</span><span> 9</span> v.add("Test0"<span>);
</span><span>10</span> v.add("Test2"<span>);
</span><span>11</span> v.add("Test2"<span>);
</span><span>12</span>
<span>13</span> <span>
<span>14</span> v.remove("Test0"); <span>
<span>15</span> v.remove(0); <span>
</span><span>16</span>
<span>17</span> <span>
<span>18</span> <span>int</span> size =<span> v.size();
</span><span>19</span> System.out.println("size:" +<span> size);
</span><span>20</span>
<span>21</span> <span>
<span>22</span> <span>for</span>(<span>int</span> i = 0;i < v.size();i++<span>){
</span><span>23</span> <span> System.out.println(v.get(i));
</span><span>24</span> <span> }
</span><span>25</span> }
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代码很简单啦，学过数据结构的都知道，简单的新增改查啦，不过我们要深入一下了解，这玩意跟数组有什么区别
构造函数如下，意思是说你可以初始化一个容量的数，多少你自己决定
1 2 3 4 5 6 7 8 9 10 11 | <span> 1</span> <span>
</span>
<span> 9</span> <span>public</span> Vector(<span>int</span><span> initialCapacity) {
</span><span>10</span> <span>this</span>(initialCapacity, 0<span>);
</span><span>11</span> }
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我们接着来看，java的构造函数可真的比php强大，支持不同参数调用，换php的话早就报错啦
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 | <span> 1</span> <span>
</span>
<span>11</span> <span>public</span> Vector(<span>int</span> initialCapacity, <span>int</span><span> capacityIncrement) {
</span><span>12</span> <span>super</span><span>();
</span><span>13</span> <span>if</span> (initialCapacity < 0<span>)
</span><span>14</span> <span>throw</span> <span>new</span> IllegalArgumentException("Illegal Capacity: "+
<span>15</span> <span> initialCapacity);
</span><span>16</span> <span>this</span>.elementData = <span>new</span><span> Object[initialCapacity];
</span><span>17</span> <span>this</span>.capacityIncrement =<span> capacityIncrement;
</span><span>18</span> }
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代码是不是很简单，简单的初始化一个对象数组，连我一个高中生的看出来啦，注意到第二个参数，这个是控制数组填满了之后要怎么增加，可以理解为一个策略吧
我们来看看添加元素是怎样实现的
1 2 3 4 5 6 7 8 9 10 11 12 13 | <span> 1</span> <span>
</span>
<span> 8</span> <span>public</span> <span>synchronized</span> <span>boolean</span><span> add(E e) {
</span><span> 9</span> modCount++<span>;
</span><span>10</span> ensureCapacityHelper(elementCount + 1<span>);
</span><span>11</span> elementData[elementCount++] =<span> e;
</span><span>12</span> <span>return</span> <span>true</span><span>;
</span><span>13</span> }
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1 | <span>synchronized 这玩意就是多线程安全的时候用的，防止多个线程同事操作</span><br /><br /><span>关键是 ensureCapacityHelper 这个函数<br /><br /></span>
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 | <span> 1</span> <span>
</span>
<span> 9</span> <span>private</span> <span>void</span> ensureCapacityHelper(<span>int</span><span> minCapacity) {
</span><span>10</span> <span>int</span> oldCapacity =<span> elementData.length;
</span><span>11</span> <span>if</span> (minCapacity ><span> oldCapacity) {
</span><span>12</span> Object[] oldData =<span> elementData;
</span><span>13</span> <span>int</span> newCapacity = (capacityIncrement > 0) ?
<span>14</span> (oldCapacity + capacityIncrement) : (oldCapacity * 2<span>);
</span><span>15</span> <span>if</span> (newCapacity <<span> minCapacity) {
</span><span>16</span> newCapacity =<span> minCapacity;
</span><span>17</span> <span> }
</span><span>18</span> elementData =<span> Arrays.copyOf(elementData, newCapacity);
</span><span>19</span> <span> }
</span><span>20</span> }
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1 | <span><br />可以这么理解吧，上面这段代码就是看看数组满了没有，如果满了就动态的增加，还记得我们上面说的那个参数吗，就是可以理解为扩展因子，如果没有定义的话就double增加，就是这么简单，貌似跟c语言的动态数组好像啊<br /><br />总结一下<br /><br />上面我们学到的知识点<br /><br /></span>
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1 | 1. synchronized 同步用的，相当于一个锁吧
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1 | <span><br />2. Arrays.copyOf 这函数是从一个数组复制到一个新数组里面，新数组容量可以自己定义<br /><br />3. java 的构造函数可以支持多个，前提你每个构造函数的参数都不同<br /><br />4. vector 这东西跟数组没什么区别，只不过它比静态数组可以自动扩展罢了<br />今天就到这里吧</span>
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1 | <span><br /><br /></span>
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1 | <span><br /><br /></span>
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