Java基础：Java的Number和Math类

落日映苍穹つ 2024-03-31 11:51 34阅读 0赞

#### 文章目录 ####

*  一、Java Math 类
 *  二、Number & Math 类方法
 *  三、Math 的 floor,round 和 ceil 方法实例比较

## 一、Java Math 类 ##

Java 的 Math 包含了用于执行基本数学运算的属性和方法，如初等指数、对数、平方根和三角函数。

Math 的方法都被定义为 static 形式，通过 Math 类可以在主函数中直接调用。

**代码如下：**

public class Test {
          
        public static void main (String []args)  
        {
          
            System.out.println("90 度的正弦值：" + Math.sin(Math.PI/2));  
            System.out.println("0度的余弦值：" + Math.cos(0));  
            System.out.println("60度的正切值：" + Math.tan(Math.PI/3));  
            System.out.println("1的反正切值： " + Math.atan(1));  
            System.out.println("π/2的角度值：" + Math.toDegrees(Math.PI/2));  
            System.out.println(Math.PI);  
        }  
    }

**结果：**

90 度的正弦值：1.0
    0度的余弦值：1.0
    60度的正切值：1.7320508075688767
    1的反正切值： 0.7853981633974483
    π/2的角度值：90.0
    3.141592653589793

## 二、Number & Math 类方法 ##

<table> 
 <thead> 
  <tr> 
   <th align="left">序号</th> 
   <th align="left">方法与描述</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td align="left">1</td> 
   <td align="left"><a href="https://www.runoob.com/java/number-xxxvalue.html" rel="nofollow">xxxValue()</a> 将 Number 对象转换为xxx数据类型的值并返回。</td> 
  </tr> 
  <tr> 
   <td align="left">2</td> 
   <td align="left"><a href="https://www.runoob.com/java/number-compareto.html" rel="nofollow">compareTo()</a> 将number对象与参数比较。</td> 
  </tr> 
  <tr> 
   <td align="left">3</td> 
   <td align="left"><a href="https://www.runoob.com/java/number-equals.html" rel="nofollow">equals()</a> 判断number对象是否与参数相等。</td> 
  </tr> 
  <tr> 
   <td align="left">4</td> 
   <td align="left"><a href="https://www.runoob.com/java/number-valueof.html" rel="nofollow">valueOf()</a> 返回一个 Number 对象指定的内置数据类型</td> 
  </tr> 
  <tr> 
   <td align="left">5</td> 
   <td align="left"><a href="https://www.runoob.com/java/number-tostring.html" rel="nofollow">toString()</a> 以字符串形式返回值。</td> 
  </tr> 
  <tr> 
   <td align="left">6</td> 
   <td align="left"><a href="https://www.runoob.com/java/number-parseInt.html" rel="nofollow">parseInt()</a> 将字符串解析为int类型。</td> 
  </tr> 
  <tr> 
   <td align="left">7</td> 
   <td align="left"><a href="https://www.runoob.com/java/number-abs.html" rel="nofollow">abs()</a> 返回参数的绝对值。</td> 
  </tr> 
  <tr> 
   <td align="left">8</td> 
   <td align="left"><a href="https://www.runoob.com/java/number-ceil.html" rel="nofollow">ceil()</a> 返回大于等于( &gt;= )给定参数的的最小整数，类型为双精度浮点型。</td> 
  </tr> 
  <tr> 
   <td align="left">9</td> 
   <td align="left"><a href="https://www.runoob.com/java/number-floor.html" rel="nofollow">floor()</a> 返回小于等于（&lt;=）给定参数的最大整数 。</td> 
  </tr> 
  <tr> 
   <td align="left">10</td> 
   <td align="left"><a href="https://www.runoob.com/java/number-rint.html" rel="nofollow">rint()</a> 返回与参数最接近的整数。返回类型为double。</td> 
  </tr> 
  <tr> 
   <td align="left">11</td> 
   <td align="left"><a href="https://www.runoob.com/java/number-round.html" rel="nofollow">round()</a> 它表示<strong>四舍五入</strong>，算法为 <strong>Math.floor(x+0.5)</strong>，即将原来的数字加上 0.5 后再向下取整，所以，Math.round(11.5) 的结果为12，Math.round(-11.5) 的结果为-11。</td> 
  </tr> 
  <tr> 
   <td align="left">12</td> 
   <td align="left"><a href="https://www.runoob.com/java/number-min.html" rel="nofollow">min()</a> 返回两个参数中的最小值。</td> 
  </tr> 
  <tr> 
   <td align="left">13</td> 
   <td align="left"><a href="https://www.runoob.com/java/number-max.html" rel="nofollow">max()</a> 返回两个参数中的最大值。</td> 
  </tr> 
  <tr> 
   <td align="left">14</td> 
   <td align="left"><a href="https://www.runoob.com/java/number-exp.html" rel="nofollow">exp()</a> 返回自然数底数e的参数次方。</td> 
  </tr> 
  <tr> 
   <td align="left">15</td> 
   <td align="left"><a href="https://www.runoob.com/java/number-log.html" rel="nofollow">log()</a> 返回参数的自然数底数的对数值。</td> 
  </tr> 
  <tr> 
   <td align="left">16</td> 
   <td align="left"><a href="https://www.runoob.com/java/number-pow.html" rel="nofollow">pow()</a> 返回第一个参数的第二个参数次方。</td> 
  </tr> 
  <tr> 
   <td align="left">17</td> 
   <td align="left"><a href="https://www.runoob.com/java/number-sqrt.html" rel="nofollow">sqrt()</a> 求参数的算术平方根。</td> 
  </tr> 
  <tr> 
   <td align="left">18</td> 
   <td align="left"><a href="https://www.runoob.com/java/number-sin.html" rel="nofollow">sin()</a> 求指定double类型参数的正弦值。</td> 
  </tr> 
  <tr> 
   <td align="left">19</td> 
   <td align="left"><a href="https://www.runoob.com/java/number-cos.html" rel="nofollow">cos()</a> 求指定double类型参数的余弦值。</td> 
  </tr> 
  <tr> 
   <td align="left">20</td> 
   <td align="left"><a href="https://www.runoob.com/java/number-tan.html" rel="nofollow">tan()</a> 求指定double类型参数的正切值。</td> 
  </tr> 
  <tr> 
   <td align="left">21</td> 
   <td align="left"><a href="https://www.runoob.com/java/number-asin.html" rel="nofollow">asin()</a> 求指定double类型参数的反正弦值。</td> 
  </tr> 
  <tr> 
   <td align="left">22</td> 
   <td align="left"><a href="https://www.runoob.com/java/number-acos.html" rel="nofollow">acos()</a> 求指定double类型参数的反余弦值。</td> 
  </tr> 
  <tr> 
   <td align="left">23</td> 
   <td align="left"><a href="https://www.runoob.com/java/number-atan.html" rel="nofollow">atan()</a> 求指定double类型参数的反正切值。</td> 
  </tr> 
  <tr> 
   <td align="left">24</td> 
   <td align="left"><a href="https://www.runoob.com/java/number-atan2.html" rel="nofollow">atan2()</a> 将笛卡尔坐标转换为极坐标，并返回极坐标的角度值。</td> 
  </tr> 
  <tr> 
   <td align="left">25</td> 
   <td align="left"><a href="https://www.runoob.com/java/number-todegrees.html" rel="nofollow">toDegrees()</a> 将参数转化为角度。</td> 
  </tr> 
  <tr> 
   <td align="left">26</td> 
   <td align="left"><a href="https://www.runoob.com/java/number-toradians.html" rel="nofollow">toRadians()</a> 将角度转换为弧度。</td> 
  </tr> 
  <tr> 
   <td align="left">27</td> 
   <td align="left"><a href="https://www.runoob.com/java/number-random.html" rel="nofollow">random()</a> 返回一个随机数。</td> 
  </tr> 
 </tbody> 
</table>

## 三、Math 的 floor,round 和 ceil 方法实例比较 ##

*  Math.floor()：意为地板，向下取整。
 *  Math.round()：四舍五入的意思，先把值+0.5，再向下取整。
 *  Math.ceil()：意为天花板，向上取整。

**代码实例：**

public class Main {
           
      public static void main(String[] args) {
           
        double[] nums = {
         1.4, 1.5, 1.6, -1.4, -1.5, -1.6 };   
        for (double num : nums) {
           
          test(num);   
        }   
      }   
      
      private static void test(double num) {
           
        System.out.println("Math.floor(" + num + ")=" + Math.floor(num));   
        System.out.println("Math.round(" + num + ")=" + Math.round(num));   
        System.out.println("Math.ceil(" + num + ")=" + Math.ceil(num));   
      }   
    }

**结果：**

Math.floor(1.4)=1.0
    Math.round(1.4)=1
    Math.ceil(1.4)=2.0
    Math.floor(1.5)=1.0
    Math.round(1.5)=2
    Math.ceil(1.5)=2.0
    Math.floor(1.6)=1.0
    Math.round(1.6)=2
    Math.ceil(1.6)=2.0
    Math.floor(-1.4)=-2.0
    Math.round(-1.4)=-1
    Math.ceil(-1.4)=-1.0
    Math.floor(-1.5)=-2.0
    Math.round(-1.5)=-1
    Math.ceil(-1.5)=-1.0
    Math.floor(-1.6)=-2.0
    Math.round(-1.6)=-2
    Math.ceil(-1.6)=-1.0