标识符： java所有组成部分都叫标识符
在代码中定义关键字
如：String ( ) (空格 =空格) “ ” ；
java中默认的标识符
abstract assert boolean break byte
case catch char class const
continue defauit do double else
for goto if finally float
instanceof int interface long native
new package private protected public
return strctfp short static super
switch synchronized this throw throws
transient try void volatile while
