how to know what a valid name for a variable is in java

In Java, a valid name for a variable must follow the rules for naming variables in the Java language.

According to the Java Language Specification (JLS), the rules for naming variables in Java are as follows:

1. A variable name must start with a letter, an underscore (_), or a dollar sign ($).

2. After the first character, a variable name can contain letters, digits, underscores, and dollar signs.

3. A variable name cannot be a reserved word in the Java language.

4. A variable name is case-sensitive.

Here are some examples of valid variable names in Java:

• x
• y
• z
• a
• b
• c
• foo
• bar
• baz
• _private
• $amount
• myVariable

And here are some examples of invalid variable names in Java:

• 123 (starts with a digit)
• true (a reserved word in the Java language)
• void (a reserved word in the Java language)
• my-variable (contains a hyphen)

Keep in mind that, while it is possible to use dollar signs and underscores in variable names, it is generally considered good programming practice to avoid using them, as they can make the code harder to read and understand.

It is also a good idea to choose descriptive and meaningful names for your variables, as this can make your code more self-explanatory and easier to maintain.