Java提供了一些预定义的数据类型,称为内置数据类型。Java还允许自定义数据类型,这样的数据类型称为用户定义的数据类型。由不可分割值组成的数据类型,但不基于任何其他数据类型来定义称为原始数据类型。

Java提供了许多内置的原始数据类型,例如intfloatbooleanchar等。在应用中可以为int数据类型的值指定名称。

int i;  

标识符

Java中的标识符是无限长的字符序列。字符序列包括所有Java字母和Java数字,但第一个必须是Java字母。

Java使用Unicode字符集。 Java字母是由Unicode字符集表示的任何语言的字母。 例如,A-Za-z_(下划线)和$被视为来自Unicode的ASCII字符集范围的Java字母。

Java数字包括0-9个ASCII数字,表示语言中数字的任何Unicode字符。

标识符中不允许有空格。标识符是用于在Java程序中的类,方法,变量等的名称。有关Java中标识符的三个重要事项:

  • 标识符中使用的字符数没有限制。
  • 标识符中使用的不仅来自ASCII字符集,字符也可以是Unicode字符集。
  • 标识符区分大小写。

关键词

Java定义了一个名为关键字的单词列表。关键字是在Java中具有预定义含义的字母,它们只能在Java语言定义的上下文中使用。Java中的关键字不能用作标识符。Java关键字的完整列表如下所示。

abstract            assert           boolean          break  byte                case             catch            char  class               const            continue         default  do                  double           else             enum  extends             final            finally          float  for                 goto             if               implements  import              instanceof       int              interface  long                native           new              package  private             protected        public           return  short               static           strictfp         super  switch              synchronized     this             throw  throws              transient        try              void  volatile            while  

两个关键字constgoto目前未在Java中使用。但它们是保留的关键字,不能用作标识符。
除了所有关键字,有三个字母:truefalsenull不能用作标识符; truefalse是布尔文字(或布尔常量),null是引用字面量。


本文属作者原创,转载请注明出处:易百教程 » Java数据类型教程

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