Java 基础类型 —— Long

灰太狼 2023-05-29 13:04 15阅读 0赞

### 文章目录 ###

*   *  1 Long 类方法
     *   *  1.1 toXXXString
         *  1.2 parseLong(...) —— 将各种格式的 String 转成 long
         *  1.3 valueOf —— 将 String、long 转成 Long
         *  1.4 getLong—— 获取系统参数值，并转换为 Long
         *  1.5 compare —— long 值比较
         *  1.6 unsigned long 的除/取余
         *  1.7 取 long 值最高/低位 1 对应的 值
         *  1.8 LeadingZeros/TrailingZeros/countBit
         *  1.9 long 对应二进制的反转
         *  1.10 sinum/sum/max/min
         *  1.11 decode/hashCode/stringSize
         *  1.12 构造函数 Long(String)
     *  2 重点方法解析
     *  参考

## 1 Long 类方法 ##

*  返回类型标 \* 的是重点方法

### 1.1 toXXXString ###

<table> 
 <thead> 
  <tr> 
   <th>返回类型</th> 
   <th>方法名</th> 
   <th>描述</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>String</td> 
   <td>toString()</td> 
   <td>toString(value)</td> 
  </tr> 
  <tr> 
   <td>* static String</td> 
   <td>toString(long i)</td> 
   <td>有意思，这和 i+"" 区别在哪呢？内部调用 getChar()</td> 
  </tr> 
  <tr> 
   <td>* static String</td> 
   <td>toString(long i, int radix)</td> 
   <td>将 long 值转成 对应进制的 String 形式</td> 
  </tr> 
  <tr> 
   <td>static String</td> 
   <td>toUnsignedString(long i)</td> 
   <td>toUnsignedString(long i,10)</td> 
  </tr> 
  <tr> 
   <td>static String</td> 
   <td>toUnsignedString(long i, int radix)</td> 
   <td>内部调用 toUnsignedString0(long val, int shift)</td> 
  </tr> 
  <tr> 
   <td>static String</td> 
   <td>toHexString(long i)</td> 
   <td>toUnsignedString0(i, 4)</td> 
  </tr> 
  <tr> 
   <td>static String</td> 
   <td>toOctalString(long i)</td> 
   <td>toUnsignedString0(i, 3)</td> 
  </tr> 
  <tr> 
   <td>static String</td> 
   <td>toBinaryString(long i)</td> 
   <td>toUnsignedString0(i, 1)</td> 
  </tr> 
  <tr> 
   <td>static String</td> 
   <td>toUnsignedString0(long val, int shift)</td> 
   <td>内部是全是通过 val &amp; mask，val &gt;&gt;&gt;= shift，所以仅仅是通过 mask 取到每一部分的值对应的 radix，所以是无符号的</td> 
  </tr> 
  <tr> 
   <td>* static String</td> 
   <td>formatUnsignedLong(…)</td> 
   <td>toUnsignedString0 内部调用它，进行的掩模计算</td> 
  </tr> 
  <tr> 
   <td>* static BigInteger</td> 
   <td>toUnsignedBigInteger(long i)</td> 
   <td>内部调用 BigInteger.valueOf(i)</td> 
  </tr> 
 </tbody> 
</table>

### 1.2 parseLong(…) —— 将各种格式的 String 转成 long ###

<table> 
 <thead> 
  <tr> 
   <th>返回类型</th> 
   <th>方法名</th> 
   <th>描述</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>static long</td> 
   <td>parseLong(String s)</td> 
   <td>parseLong(String s, 10)</td> 
  </tr> 
  <tr> 
   <td>* static long</td> 
   <td>parseLong(String s, int radix)</td> 
   <td>根据对应的进制，将 s 解析成对应的 long 值，用负数算(有意思)</td> 
  </tr> 
  <tr> 
   <td>static long</td> 
   <td>parseUnsignedLong(String s)</td> 
   <td>parseUnsignedLong(String s, 10)</td> 
  </tr> 
  <tr> 
   <td>* static long</td> 
   <td>parseUnsignedLong(String s, int radix)</td> 
   <td>内部调用 parseLong(String s, int radix) 做处理</td> 
  </tr> 
 </tbody> 
</table>

### 1.3 valueOf —— 将 String、long 转成 Long ###

<table> 
 <thead> 
  <tr> 
   <th>返回类型</th> 
   <th>方法名</th> 
   <th>描述</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>static Long</td> 
   <td>valueOf(String s)</td> 
   <td>Integer.valueOf(parseLong(s, 10))</td> 
  </tr> 
  <tr> 
   <td>static Long</td> 
   <td>valueOf(String s, int radix)</td> 
   <td>Integer.valueOf(parseLong(s,radix))</td> 
  </tr> 
  <tr> 
   <td>static Long</td> 
   <td>valueOf(long l)</td> 
   <td>内部走Cache,LongCache 的范围固定 [-128,127]</td> 
  </tr> 
 </tbody> 
</table>

### 1.4 getLong—— 获取系统参数值，并转换为 Long ###

<table> 
 <thead> 
  <tr> 
   <th>返回类型</th> 
   <th>方法名</th> 
   <th>描述</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>static Long</td> 
   <td>getLong(String nm)</td> 
   <td>getLong(nm, null)</td> 
  </tr> 
  <tr> 
   <td>static Long</td> 
   <td>getLong(String nm, long val)</td> 
   <td>内部调用 getLong(nm, null)</td> 
  </tr> 
  <tr> 
   <td>static Long</td> 
   <td>getLong(String nm, Long val)</td> 
   <td>获取系统 property 参数值，v = System.getProperty(nm)，如果为 null，返回 val 值</td> 
  </tr> 
 </tbody> 
</table>

### 1.5 compare —— long 值比较 ###

<table> 
 <thead> 
  <tr> 
   <th>返回类型</th> 
   <th>方法名</th> 
   <th>描述</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>int</td> 
   <td>compareTo(Long anotherLong)</td> 
   <td>compare(this.value, anotherInteger.value)</td> 
  </tr> 
  <tr> 
   <td>static int</td> 
   <td>compare(long x, long y)</td> 
   <td>(x &lt; y) ? -1 : ((x == y) ? 0 : 1)</td> 
  </tr> 
  <tr> 
   <td>static int</td> 
   <td>compareUnsigned(long x, long y)</td> 
   <td>compare(x + MIN_VALUE, y + MIN_VALUE)</td> 
  </tr> 
 </tbody> 
</table>

### 1.6 unsigned long 的除/取余 ###

<table> 
 <thead> 
  <tr> 
   <th>返回类型</th> 
   <th>方法名</th> 
   <th>描述</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>static long</td> 
   <td>divideUnsigned(long dividend, long divisor)</td> 
   <td>toUnsignedBigInteger(dividend). divide(toUnsignedBigInteger(divisor)).longValue()</td> 
  </tr> 
  <tr> 
   <td>static long</td> 
   <td>remainderUnsigned(long dividend, long divisor)</td> 
   <td>toUnsignedBigInteger(dividend). remainder(toUnsignedBigInteger(divisor)).longValue()</td> 
  </tr> 
 </tbody> 
</table>

### 1.7 取 long 值最高/低位 1 对应的 值 ###

<table> 
 <thead> 
  <tr> 
   <th>返回类型</th> 
   <th>方法名</th> 
   <th>描述</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>* static long</td> 
   <td>highestOneBit(long i)</td> 
   <td>最高位取最高 1 及后面全置0的值，<a href="https://blog.csdn.net/jessenpan/article/details/9617749" rel="nofollow">代码解析</a></td> 
  </tr> 
  <tr> 
   <td>* static long</td> 
   <td>lowestOneBit(long i)</td> 
   <td>i &amp; -i</td> 
  </tr> 
 </tbody> 
</table>

### 1.8 LeadingZeros/TrailingZeros/countBit ###

<table> 
 <thead> 
  <tr> 
   <th>返回类型</th> 
   <th>方法名</th> 
   <th>描述</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>* static int</td> 
   <td>numberOfLeadingZeros(long i)</td> 
   <td>i 对应 2 进制的开头 0 的个数</td> 
  </tr> 
  <tr> 
   <td>* static int</td> 
   <td>numberOfTrailingZeros(long i)</td> 
   <td>i 对应 2 进制的末尾 0 的个数</td> 
  </tr> 
  <tr> 
   <td>* static int</td> 
   <td>bitCount(long i)</td> 
   <td>i 对应 2 进制中 1 的个数</td> 
  </tr> 
 </tbody> 
</table>

### 1.9 long 对应二进制的反转 ###

<table> 
 <thead> 
  <tr> 
   <th>返回类型</th> 
   <th>方法名</th> 
   <th>描述</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>* static long</td> 
   <td>rotateLeft(long i, int distance)</td> 
   <td>(i &lt;&lt; distance) | (i &gt;&gt;&gt; -distance)</td> 
  </tr> 
  <tr> 
   <td>* static long</td> 
   <td>rotateRight(long i, int distance)</td> 
   <td>(i &gt;&gt;&gt; distance) | (i &lt;&lt; -distance)</td> 
  </tr> 
  <tr> 
   <td>* static long</td> 
   <td>reverse(long i)</td> 
   <td><a href="https://www.jianshu.com/p/be272c8704d9" rel="nofollow">二进制按位反转</a> ：对应的2进制180°反转</td> 
  </tr> 
  <tr> 
   <td>* static long</td> 
   <td>reverseBytes(long i)</td> 
   <td><a href="https://www.jianshu.com/p/be272c8704d9" rel="nofollow">二进制按byte反转</a></td> 
  </tr> 
 </tbody> 
</table>

00000000_00000000_01001101_00011111 -> 原始
    11111000_10110010_00000000_00000000 -> 按位反转
    00011111_01001101_00000000_00000000 -> 按字节反转

### 1.10 sinum/sum/max/min ###

<table> 
 <thead> 
  <tr> 
   <th>返回类型</th> 
   <th>方法名</th> 
   <th>描述</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>static long</td> 
   <td>signum(long i)</td> 
   <td>负数返回 -1，0 返回 0，正数返回 1</td> 
  </tr> 
  <tr> 
   <td>static long</td> 
   <td>sum(long a, long b)</td> 
   <td>a + b</td> 
  </tr> 
  <tr> 
   <td>static long</td> 
   <td>max(long a, long b)</td> 
   <td>Math.max(a, b)</td> 
  </tr> 
  <tr> 
   <td>static long</td> 
   <td>min(long a, long b)</td> 
   <td>Math.min(a, b)</td> 
  </tr> 
 </tbody> 
</table>

### 1.11 decode/hashCode/stringSize ###

<table> 
 <thead> 
  <tr> 
   <th>返回类型</th> 
   <th>方法名</th> 
   <th>描述</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>static int</td> 
   <td>stringSize(long x)</td> 
   <td>x 的位数，x 必须为非负</td> 
  </tr> 
  <tr> 
   <td>int</td> 
   <td>hashCode()</td> 
   <td>Long.hashCode(value)</td> 
  </tr> 
  <tr> 
   <td>static int</td> 
   <td>hashCode(long value)</td> 
   <td>(int)(value ^ (value &gt;&gt;&gt; 32))</td> 
  </tr> 
  <tr> 
   <td>* static Long</td> 
   <td>decode(String nm)</td> 
   <td>根据 nm 的类型，判断它的进制，然后转成 10 进制 Long</td> 
  </tr> 
 </tbody> 
</table>

### 1.12 构造函数 Long(String) ###

*  内部调用 parseLong(s,10)
 *  如果确定 long 很小，推荐使用 Long.valueOf(String)：这样可以走 cache

## 2 重点方法解析 ##

*  留待以后补充

## 参考 ##

jdk1.8\_171