Java中的8种原生数据类型(Primitive Data Types)分析

╰半橙微兮° 2022-05-12 07:18 165阅读 0赞

八种数据类型

<table style="width:500px;"> 
 <tbody> 
  <tr> 
   <td>类型</td> 
   <td><strong>&nbsp;int&nbsp; </strong></td> 
   <td><strong>&nbsp;short</strong></td> 
   <td><strong>&nbsp;long</strong></td> 
   <td><strong>&nbsp;byte</strong></td> 
   <td><strong>&nbsp;float</strong></td> 
   <td><strong>&nbsp;double</strong></td> 
   <td><strong>&nbsp;char</strong></td> 
   <td><strong>&nbsp;boolean</strong></td> 
  </tr> 
  <tr> 
   <td>字节数</td> 
   <td>4</td> 
   <td>2</td> 
   <td>8</td> 
   <td>1</td> 
   <td>4</td> 
   <td>8</td> 
   <td>4</td> 
   <td>&nbsp;JVM相关</td> 
  </tr> 
  <tr> 
   <td>大小</td> 
   <td>-2147483648~2147483647</td> 
   <td>-32768~32767</td> 
   <td>-9223372036854775808~9223372036854775807</td> 
   <td>-128~127</td> 
   <td>±3.40282347E+38F</td> 
   <td>±1.79769313486231570E+308</td> 
   <td>&nbsp;</td> 
   <td>&nbsp;</td> 
  </tr> 
 </tbody> 
</table>

> tip:八种类型我是这样记忆的：boolean,char是我们常用的，double是**双**精度浮点小数，有双就有单 : float是单精度浮点小数,int是一个坐标，short比int短，long比int长，byte是整数的最小单位.

以下是官方文档，我翻译一下。（重点在于boolean值的描述）

*  **byte**: The `byte` data type is an 8-bit signed two's complement integer. It has a minimum value of -128 and a maximum value of 127 (inclusive). The `byte` data type can be useful for saving memory in large [arrays][], where the memory savings actually matters. They can also be used in place of `int` where their limits help to clarify your code; the fact that a variable's range is limited can serve as a form of documentation.

byte数据类型是一个8-bit有符号的二进制补码整数。取值范围：【-128，127】，当内存比较重要的时候：比如超大数组的情况。

*  **short**: The `short` data type is a 16-bit signed two's complement integer. It has a minimum value of -32,768 and a maximum value of 32,767 (inclusive). As with `byte`, the same guidelines apply: you can use a `short` to save memory in large arrays, in situations where the memory savings actually matters.

short是一个16-bit 的二进制补码整数，取值范围：\[-32768,32767\]。同上文byte.

*  **int**: By default, the `int` data type is a 32-bit signed two's complement integer, which has a minimum value of -2\*31 and a maximum value of 231-1.   In Java SE 8 and later, you can use the `int` data type to represent an unsigned 32-bit integer, which has a minimum value of 0 and a maximum value of 2\*32-1. Use the Integer class to use `int` data type as an unsigned integer. See the section The Number Classes for more information. Static methods like `compareUnsigned`, `divideUnsigned` etc have been added to the [`Integer`][Integer] class to support the arithmetic operations for unsigned integers.

默认情况下，int是32-bit的二进制补码整数，取值范围是:\[-2^31,2^31-1\]，在JavaSE8以后，你可以使用int数据类型去展现一个无符号为的32-bit的值(取值范围：\[0,2^32 - 1\]),使用Integer类去操作无符号为的Integer，具体情况请参考Number类。包含`compareUnsigned`, `divideUnsigned等静态方法.`

*  **long**: The `long` data type is a 64-bit two's complement integer. The signed long has a minimum value of -263 and a maximum value of 263-1. In Java SE 8 and later, you can use the `long` data type to represent an unsigned 64-bit long, which has a minimum value of 0 and a maximum value of 264-1. Use this data type when you need a range of values wider than those provided by `int`. The [`Long`][Long] class also contains methods like `compareUnsigned`, `divideUnsigned` etc to support arithmetic operations for unsigned long.

几乎同int，除了不包含`compareUnsigned`, `divideUnsigned等静态方法。`

*  **float**: The `float` data type is a single-precision 32-bit IEEE 754 floating point. Its range of values is beyond the scope of this discussion, but is specified in the [Floating-Point Types, Formats, and Values][Floating-Point Types_ Formats_ and Values] section of the Java Language Specification. As with the recommendations for `byte` and `short`, use a `float` (instead of `double`) if you need to save memory in large arrays of floating point numbers. This data type should never be used for precise values, such as currency. For that, you will need to use the [java.math.BigDecimal][] class instead. [Numbers and Strings][] covers `BigDecimal` and other useful classes provided by the Java platform.

float是单精度的浮点小数.存在的意义类似于short，省内存.

*  **double**: The `double` data type is a double-precision 64-bit IEEE 754 floating point. Its range of values is beyond the scope of this discussion, but is specified in the [Floating-Point Types, Formats, and Values][Floating-Point Types_ Formats_ and Values] section of the Java Language Specification. For decimal values, this data type is generally the default choice. As mentioned above, this data type should never be used for precise values, such as currency.

double是我们在十进制小数情况下的默认选择，但是注意，不要把他当做通用的类.

*  **boolean**: The `boolean` data type has only two possible values: `true` and `false`. Use this data type for simple flags that track true/false conditions. This data type represents one bit of information, but its "size" isn't something that's precisely defined.

注意：boolean的内存大小是和JVM有关的。布尔值不能与整型值相互转换

*  **char**: The `char` data type is a single 16-bit Unicode character. It has a minimum value of `'\u0000'` (or 0) and a maximum value of `'\uffff'` (or 65,535 inclusive).,四个字节.

char四个字节.

额外说一句：“我们强烈建议不要再程序中使用char类型，除非确定需要处理UTF-16代码单元，最好将字符串作为抽象数据类型处理”.------《Java核心技术卷 卷1》p35

最后：Java没有任何无符号(unsigned)形式的int,long,short或byte类型.

[arrays]: https://docs.oracle.com/javase/tutorial/java/nutsandbolts/arrays.html
[Integer]: https://docs.oracle.com/javase/8/docs/api/java/lang/Integer.html
[Long]: https://docs.oracle.com/javase/8/docs/api/java/lang/Long.html
[Floating-Point Types_ Formats_ and Values]: https://docs.oracle.com/javase/specs/jls/se7/html/jls-4.html#jls-4.2.3
[java.math.BigDecimal]: https://docs.oracle.com/javase/8/docs/api/java/math/BigDecimal.html
[Numbers and Strings]: https://docs.oracle.com/javase/tutorial/java/data/index.html