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<time class="level-item has-text-grey" datetime="2013-07-11T05:41:45.000Z">2013-07-11</time>
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3 分钟 读完 (大约 513 个字)
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一起学java之jdk常用工具类
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<h5 id="Date"><a href="#Date" class="headerlink" title="Date"></a>Date</h5><p>1.Data类位于java.util包中,表示时间 </p>
<p>2.Date该类包装了一个毫秒值,表示从1970年1月1日00:00:00 GMT开始到现在毫秒数 </p>
<a id="more"></a>
<p>3.Date类的两个常用构造方法 </p>
<ul>
<li>Date(),按照当前系统时间创建一个Date对象 </li>
<li>Date(long date),按照给定的时间毫秒值创建一个Date对象 </li>
</ul>
<p><img src="/images/20191011134515.png" alt></p>
<p>4.主要的方法 </p>
<p><img src="/images/20191011134700.png" alt></p>
<p>举例: </p>
<p><img src="/images/20191011134827.png" alt></p>
<h5 id="SimpleDateFormat"><a href="#SimpleDateFormat" class="headerlink" title="SimpleDateFormat"></a>SimpleDateFormat</h5><p>1.使用SimpleDateFormat类来格式化时间,使之成为自己想要的格式 </p>
<ul>
<li>举例: </li>
</ul>
<p><img src="/images/20191011135236.png" alt></p>
<ul>
<li>说明：yyyy表示年，MM表示月，dd表示日，HH表示24小时制的小时数，hh表示12小时制的小时数，mm表示分钟，ss表示秒 </li>
</ul>
<p>2.如何将字符串对象转换成Date对象? </p>
<ul>
<li>使用SimpleDateFormat的parse()方法 </li>
<li>举例: </li>
</ul>
<p><img src="/images/20191011135147.png" alt></p>
<h5 id="NumberFormat"><a href="#NumberFormat" class="headerlink" title="NumberFormat"></a>NumberFormat</h5><p>1.数字格式化也是在程序中常用的技巧,主要是对小数位数,表示形式等的格式化<br>2.NumberFormat使用getInstance()方法实例化<br>3.可以使用NumberFormat进行数字格式化 </p>
<p><img src="/images/20191011135454.png" alt></p>
<p>4.也可以使用Decimalformat进行数字格式化 </p>
<p><img src="/images/20191011135544.png" alt></p>
<ul>
<li>注意: <ul>
<li>#:代表一个位置数字,如果该位置数字不存在,则不显示 </li>
<li>,:代表数字中的分割符 </li>
<li>0:代表一个数字位置,如果该位置不存在,则用0来补充,小数中多余的部分四舍五入 </li>
<li>.:代表小数点 </li>
<li>E:科学计数法 </li>
<li>%:用百分号表示数字 </li>
</ul>
</li>
</ul>
<h5 id="Calendar"><a href="#Calendar" class="headerlink" title="Calendar"></a>Calendar</h5><p>1.用来记录日期的日历类Calendar </p>
<p>2.使用getInstance()方法实例化 </p>
<p>3.常用方法: </p>
<p><img src="/images/20191011135750.png" alt></p>
<ul>
<li>使用时请注意星期,月份等与实际值之间的差异 </li>
</ul>
<p>4.Calendar与Date的转换 </p>
<ul>
<li>Calendar转化为Date </li>
</ul>
<figure class="highlight plain hljs"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line">Calendar cal=Calendar.getInstance(); </span><br><span class="line"></span><br><span class="line">Date date=cal.getTime();</span><br></pre></td></tr></table></figure>
<ul>
<li>Date转化为Calendar </li>
</ul>
<figure class="highlight plain hljs"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line">Date date=new Date(); </span><br><span class="line"></span><br><span class="line">Calendar cal=Calendar.getInstance(); </span><br><span class="line"></span><br><span class="line">cal.setTime(date);</span><br></pre></td></tr></table></figure>
<h5 id="Math"><a href="#Math" class="headerlink" title="Math"></a>Math</h5><p>1.java.lang.Math类包含了许多常用数学运算,全部为静态方法 </p>
<p>2.方法举例: </p>
<p><img src="/images/20191011135953.png" alt></p>
<p>3.两个常用的常量,Math.E和Math.PI分别表示自然对数的底数和圆周率 </p>
<p><img src="/images/20191011140052.png" alt></p>
<p>4.还有其他方法,使用时勤查API文档即可 </p>
</div>
<ul class="post-copyright">
<li><strong>本文标题：</strong><a href="https://blog.visutech.cn/55382.html">一起学java之jdk常用工具类</a></li>
<li><strong>本文作者：</strong><a href="https://blog.visutech.cn">程振奇 | smallodd</a></li>
<li><strong>本文链接：</strong><a href="https://blog.visutech.cn/55382.html">https://blog.visutech.cn/55382.html</a></li>
<li><strong>发布时间：</strong>2013-07-11</li>
<li><strong>版权声明：</strong>本博客所有文章除特别声明外，均采用 <a href="https://creativecommons.org/licenses/by-nc-sa/4.0/deed.zh" rel="external nofollow" target="_blank">CC BY-NC-SA 4.0</a> 许可协议。转载请注明出处！
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