What are the illegal identifiers in Java?

Identifiers that do not conform to Java syntax rules are considered illegal and they will cause compilation errors. Illegal identifiers include: Contains spaces Starts with a number Uses reserved words Starts with an underscore followed by a number Contains special characters (except _ and $) Is longer than 255 characters The same as a keyword Starts or ends with a period Contains a backslash Contains Unicode conversion Definition sequence

Illegal identifier in Java

Illegal identifier is not valid in Java language Names that are allowed to be used. These names do not comply with Java syntax rules and will cause compile-time errors.

The following are illegal Java identifiers:

• Contains spaces: Identifiers cannot contain spaces.
• Start with a number: Identifiers cannot start with a number.
• Use reserved words: Some words in Java are reserved words and cannot be used as identifiers, such as "class", "int", "if", etc.
• Start with an underscore followed by a number: Identifiers cannot begin with an underscore followed by a number, such as "_123".
• Contains special characters: Identifiers cannot contain any other special characters except the underscore (_) and the dollar sign ($).
• Length exceeds 255 characters: The length of the identifier cannot exceed 255 characters.
• Same as keyword: The identifier cannot be the same as any Java keyword.
• Starts or ends with a period (.): Identifiers cannot start or end with a period.
• Contains backslashes (\): Identifiers cannot contain backslashes.
• Contains Unicode escape sequences: Identifiers cannot contain Unicode escape sequences.

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