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        <h2 id="1、为什么需要变量？"><a href="#1、为什么需要变量？" class="headerlink" title="1、为什么需要变量？"></a>1、为什么需要变量？</h2><p>方便对一个数据的修改和使用。如：一个数据在多处使用时，如果要修改，那么多个地方同时都需要修改，这个需要一个变量用于存储数据，在使用时，直接使用变量即可，这样当修改数据时，只需要修改变量本身的值就可以了。</p>
<h2 id="2、什么是变量？"><a href="#2、什么是变量？" class="headerlink" title="2、什么是变量？"></a>2、什么是变量？</h2><p>在java中，变量是一个存储空间的表示。</p>
<h2 id="3、使用变量的语法："><a href="#3、使用变量的语法：" class="headerlink" title="3、使用变量的语法："></a>3、使用变量的语法：</h2><p>数据类型 变量名 = 值</p>
<h2 id="4、数据类型"><a href="#4、数据类型" class="headerlink" title="4、数据类型"></a>4、数据类型</h2><p>基本可以分为两类：基本数据类型和引用数据类型<br>基本数据类型：整数、小数、布尔、字符<br><a id="more"></a></p>
<h3 id="整数："><a href="#整数：" class="headerlink" title="整数："></a>整数：</h3><p>byte:表示是字节  占用的内存空间是1字节<br>short:表示是短整形  占用的内存空间是2字节<br>int:表示整形 占用的内存空间是4字节<br>long:表示长整形 占用的内存空间是8字节</p>
<h3 id="小数："><a href="#小数：" class="headerlink" title="小数："></a>小数：</h3><p>float：单精度浮点数 占用的内存空间是4字节<br>double:双精度浮点数 占用的内存空间是8字节</p>
<h3 id="布尔："><a href="#布尔：" class="headerlink" title="布尔："></a>布尔：</h3><p>boolean:布尔类型的值 只有true和false 1字节</p>
<h3 id="字符：用于表示单个字符"><a href="#字符：用于表示单个字符" class="headerlink" title="字符：用于表示单个字符"></a>字符：用于表示单个字符</h3><p>char:2个字节</p>
<h3 id="引用数据类型：class-interface-数组"><a href="#引用数据类型：class-interface-数组" class="headerlink" title="引用数据类型：class ,interface,数组"></a>引用数据类型：class ,interface,数组</h3><figure class="highlight java"><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><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String[] args)</span></span>&#123;</span><br><span class="line">    <span class="keyword">byte</span> age = <span class="number">125</span> ;</span><br><span class="line">    <span class="keyword">short</span> t = <span class="number">23</span> ;</span><br><span class="line">    <span class="keyword">char</span> ch = <span class="string">'中'</span>;</span><br><span class="line">    <span class="keyword">boolean</span> flag = <span class="keyword">true</span> ;</span><br><span class="line">    <span class="keyword">float</span> score = <span class="number">98.5f</span> ;</span><br><span class="line">    <span class="keyword">double</span> avgScore = <span class="number">80.4</span> ;</span><br><span class="line">    System.out.println(age);</span><br><span class="line">    System.out.println(t);</span><br><span class="line">    System.out.println(ch);</span><br><span class="line">   System.out.println(flag);</span><br><span class="line">   System.out.println(score);</span><br><span class="line">   System.out.println(avgScore);</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>整数默认是 int,小数默认是 double<br>单精度后面的 f 表示是单精度浮点，需要明确出来，可以 f 或者 F .</p>
<h2 id="5、5-整数在java中有4种表现形式："><a href="#5、5-整数在java中有4种表现形式：" class="headerlink" title="5、5.    整数在java中有4种表现形式："></a>5、5.    整数在java中有4种表现形式：</h2><p>二进制：是由数字0和1组成的。<br>八进制：是由数字0到7组成的。<br>十进制：是由数字0到9组成的。<br>十六进制：是由数字0到9和ABCDEF组成。<br>进制之间转换：<br><img src="http://ou3xxg3hg.bkt.clouddn.com/进制.jpg" alt="进制的转换"></p>
<h2 id="6、-变量名：命名规则采用驼峰命名法。"><a href="#6、-变量名：命名规则采用驼峰命名法。" class="headerlink" title="6、    变量名：命名规则采用驼峰命名法。"></a>6、    变量名：命名规则采用驼峰命名法。</h2><h2 id="7、-数据类型的转换："><a href="#7、-数据类型的转换：" class="headerlink" title="7、    数据类型的转换："></a>7、    数据类型的转换：</h2><p>自动类型转换：<br><img src="http://ou3xxg3hg.bkt.clouddn.com/自动类型转换.jpg" alt=""><br>强制类型转换：<br><img src="http://ou3xxg3hg.bkt.clouddn.com/强制类型转换.jpg" alt=""><br>类型提升：<br>当是byte，short，char 进行运算时会自动提升为int。<br>当有float类型，提升为float类型<br>当有double类型，提升为double类型<br>当有long类型，提升为long类型<br><img src="http://ou3xxg3hg.bkt.clouddn.com/类的自动提升.jpg" alt=""></p>
<h2 id="8、-字符类型：在java中，char用来表示一个字符，一个字符也就是一个字母-用单引号括起来。’A’；也可以用char来表示一个中文。表示中文时特别需要注意编码问题。"><a href="#8、-字符类型：在java中，char用来表示一个字符，一个字符也就是一个字母-用单引号括起来。’A’；也可以用char来表示一个中文。表示中文时特别需要注意编码问题。" class="headerlink" title="8、    字符类型：在java中，char用来表示一个字符，一个字符也就是一个字母,用单引号括起来。’A’；也可以用char来表示一个中文。表示中文时特别需要注意编码问题。"></a>8、    字符类型：在java中，char用来表示一个字符，一个字符也就是一个字母,用单引号括起来。’A’；也可以用char来表示一个中文。表示中文时特别需要注意编码问题。</h2>

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