Questions: Identifiers Rules for identifiers A name created by a programmer for an item like a variable or method is called an identifier. An identifier must: - be a sequence of letters (a-z, A-Z), underscore (-), dollar signs (), and digits (0-9) - start with a letter, underscore, or dollar sign Note that "-", called an underscore, and "", called a dollar sign or currency symbol, are considered to be letters. A good practice followed by many Java programmers is to not use or in programmer-created identifiers. Identifiers are case sensitive, meaning upper and lower case letters differ. So numCats and NumCats are different. A reserved word is a word that is part of the language, like int, short, or double. A reserved word is also known as a keyword. A programmer cannot use a reserved word as an identifier. Many language editors will automatically color a program's reserved words. A list of reserved words appears at the end of this section. Check if the following identifiers are valid: c, cat, n1m1, short1, hello, 42c, hi there, and cat!

Identifiers Rules for identifiers A name created by a programmer for an item like a variable or method is called an identifier. An identifier must: - be a sequence of letters (a-z, A-Z), underscore (-), dollar signs (), and digits (0-9) - start with a letter, underscore, or dollar sign Note that "-", called an underscore, and "", called a dollar sign or currency symbol, are considered to be letters. A good practice followed by many Java programmers is to not use or in programmer-created identifiers. Identifiers are case sensitive, meaning upper and lower case letters differ. So numCats and NumCats are different. A reserved word is a word that is part of the language, like int, short, or double. A reserved word is also known as a keyword. A programmer cannot use a reserved word as an identifier. Many language editors will automatically color a program's reserved words. A list of reserved words appears at the end of this section. Check if the following identifiers are valid: c, cat, n1m1, short1, hello, 42c, hi there, and cat!
Transcript text: Identifiers Rules for identifiers A name created by a programmer for an item like a variable or method is called an identifier. An identifier must: - be a sequence of letters (a-z, A-Z), underscore $(-)$, dollar signs $(\$)$, and digits (0-9) - start with a letter, underscore, or dollar sign Note that " - , called an underscore, and " $\$$ ", called a dollar sign or currency symbol, are considered to be letters. A good practice followed by many Java programmers is to not use _ or \$ in programmer-created identifiers. Identifiers are case sensitive, meaning upper and lower case letters differ. So numCats and NumCats are different. A reserved word is a word that is part of the language, like int, short, or double. A reserved word is also known as a keyword. A programmer cannot use a reserved word as an identifier. Many language editors will automatically color a program's reserved words. A list of reserved words appears at the end of this section. Check if the following identifiers are valid: $c$, cat, $n 1 \mathrm{m1}$, short1, hello, 42 c , hi there, and cat!
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Solution

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To determine if the given identifiers are valid according to the rules provided, we need to check each identifier against the specified criteria:

  1. An identifier must be a sequence of letters (a-z, A-Z), underscores (_), dollar signs ($), and digits (0-9).
  2. An identifier must start with a letter, underscore, or dollar sign.
  3. An identifier cannot be a reserved word.

Let's evaluate each identifier:

  1. $c$:

    • Starts with a letter.
    • Contains only letters.
    • Not a reserved word.
    • Valid

  2. cat:

    • Starts with a letter.
    • Contains only letters.
    • Not a reserved word.
    • Valid

  3. $n 1 \mathrm{m1}$:

    • Contains spaces, which are not allowed.
    • Invalid

  4. short1:

    • Starts with a letter.
    • Contains letters and digits.
    • "short" is a reserved word, but "short1" is not.
    • Valid

  5. hello:

    • Starts with a letter.
    • Contains only letters.
    • Not a reserved word.
    • Valid

  6. 42 c:

    • Starts with a digit, which is not allowed.
    • Contains spaces, which are not allowed.
    • Invalid

  7. hi there:

    • Contains spaces, which are not allowed.
    • Invalid

  8. cat!:

    • Contains an exclamation mark, which is not allowed.
    • Invalid

In summary, the valid identifiers are: $c$, cat, short1, and hello.

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