java - 所有的名字都是标识符吗？

Question

在 Java 语言规范 6.2 中 Link

下面是以下代码示例:

class Test {
    public static void main(String[] args) {
        Class c = System.out.getClass();
        System.out.println(c.toString().length() +
                           args[0].length() + args.length);
    }
}

它指出:

the identifiers Test, main, and the first occurrences of args and c are not names. Rather, they are used in declarations to specify the names of the declared entities. The names String, Class, System.out.getClass, System.out.println, c.toString, args, and args.length appear in the example.

但是像 Class 和 String 这样的名字也是标识符吗？到底什么是标识符？

Answer 1

标识符是 token 的一种类型。从规范lexical structure of Java :

3.8. Identifiers

An identifier is an unlimited-length sequence of Java letters and Java digits, the first of which must be a Java letter.

Identifier:
    IdentifierChars but not a Keyword or BooleanLiteral or NullLiteral

IdentifierChars:
    JavaLetter
    IdentifierChars JavaLetterOrDigit

 JavaLetter:
     any Unicode character that is a Java letter (see below)

 JavaLetterOrDigit:
     any Unicode character that is a Java letter-or-digit (see below)

A "Java letter" is a character for which the method Character.isJavaIdentifierStart(int) returns true.

A "Java letter-or-digit" is a character for which the method Character.isJavaIdentifierPart(int) returns true.

The "Java letters" include uppercase and lowercase ASCII Latin letters A-Z (\u0041-\u005a), and a-z (\u0061-\u007a), and, for historical reasons, the ASCII underscore (_, or \u005f) and dollar sign ($, or \u0024). The $ character should be used only in mechanically generated source code or, rarely, to access pre-existing names on legacy systems.

The "Java digits" include the ASCII digits 0-9 (\u0030-\u0039).

Letters and digits may be drawn from the entire Unicode character set, which supports most writing scripts in use in the world today, including the large sets for Chinese, Japanese, and Korean. This allows programmers to use identifiers in their programs that are written in their native languages.

An identifier cannot have the same spelling (Unicode character sequence) as a keyword (§3.9), boolean literal (§3.10.3), or the null literal (§3.10.7), or a compile-time error occurs.