[TOC]

1. 原始数据类型和默认值(Primitive Data Types)

   数据类型	位数(bit)	大小	默认值
   byte	8	-128~127(inclusive)	0
   short	16	-32,768~32,767 (inclusive)	0
   int	32	-2^31~2^31-1	0
   long	64	-2^63~2^63-1	0L
   float	32		0.0f
   double	64		0.0d
   boolean			false
   char	16	0~65,535(inclusive)	'\u0000'

2. 整型(Integer Literals)

   An integer literal is of type long if it ends with the letter L or l; otherwise it is of type int. It is recommended that you use the upper case letter L because the lower case letter l is hard to distinguish from the digit 1.

   • 如果结尾是L或者是l，则是long类型，否则是int。

   • 推荐使用大写字母L，因为和1很难区分开来。

3. (浮点类型)Floating-Point Literals

   A floating-point literal is of type float if it ends with the letter F or f; otherwise its type is double and it can optionally end with the letter D or d.

   • 如果结尾是F或者f，则是浮点类型，否则是double类型

4. (字符和字符串)Character and String Literals

   Literals of types char and String may contain any Unicode (UTF-16) characters. If your editor and file system allow it, you can use such characters directly in your code. If not, you can use a "Unicode escape" such as '\u0108' (capital C with circumflex), or "S\u00ED Se\u00F1or" (Sí Señor in Spanish). Always use 'single quotes' for char literals and "double quotes" for String literals. Unicode escape sequences may be used elsewhere in a program (such as in field names, for example), not just in char or String literals.

   The Java programming language also supports a few special escape sequences for char and String literals: \b (backspace), \t (tab), \n (line feed), \f (form feed), \r (carriage return), \" (double quote), \' (single quote), and \\ (backslash).

   There's also a special null literal that can be used as a value for any reference type. null may be assigned to any variable, except variables of primitive types. There's little you can do with a null value beyond testing for its presence. Therefore, null is often used in programs as a marker to indicate that some object is unavailable.

   Finally, there's also a special kind of literal called a class literal, formed by taking a type name and appending ".class"; for example, String.class. This refers to the object (of type Class) that represents the type itself.

   • 单引号用char，双引号用String
   • 字符转义，转义序列：\ b（退格），\ t（制表符），\ n（换行），\ f（换页），\ r（回车）， \“（双引号），'（单引号）和\（反斜杠）。

问题

• 为什么最大值是2位次方-1，而不是直接是2的次方，比如byte最大值是2的8次方-1

  因为Java最低位是符号位，0是正数，1是负数。

参考资料

• 官网文档首页
• 官方文档-语言基础