Write EBNF descriptions for the following:
A Java class definition header statement
A Java method call statement
A C switch statement
A C union definition
C float literals
The correct answer and explanation is :
Here are the EBNF (Extended Backus-Naur Form) descriptions for the given statements:
1. Java Class Definition Header Statement
A Java class header defines a class in Java with possible modifiers like public, private, abstract, final, etc., followed by the class name, and optionally, the class extension or interfaces it implements.
<class-definition> ::= [ <modifier> ] "class" <identifier> [ "extends" <identifier> ] [ "implements" <identifier-list> ] "{"
<class-body>
"}"
<modifier> ::= "public" | "private" | "protected" | "abstract" | "final"
<identifier> ::= <letter> { <letter> | <digit> }
<identifier-list> ::= <identifier> { "," <identifier> }
<class-body> ::= { <class-member> }
<class-member> ::= <method-definition> | <variable-declaration>
<method-definition> ::= <modifier>* "void" <identifier> "(" <parameter-list> ")" "{"
<statement>* "}"
<parameter-list> ::= [ <parameter> { "," <parameter> } ]
<parameter> ::= <type> <identifier>
<type> ::= "int" | "float" | "boolean" | "String" | <identifier>
<statement> ::= <expression> ";" | "return" <expression> ";"Explanation:
This EBNF describes a Java class header. It includes optional modifiers such as public or abstract, followed by the class keyword, a class name (<identifier>), and optional inheritance and interface clauses. The class body contains method definitions and variable declarations.
2. Java Method Call Statement
A method call in Java is an invocation of a method that may or may not return a value and may have arguments passed to it.
<method-call> ::= <identifier> "(" [ <argument-list> ] ")"
<argument-list> ::= <expression> { "," <expression> }
<expression> ::= <identifier> | <literal> | <operation>
<literal> ::= <integer> | <string> | <float>
<operation> ::= <expression> "+" <expression> | <expression> "-" <expression>Explanation:
This describes a Java method call where a method with a name (<identifier>) is invoked with an optional list of arguments (expressions separated by commas).
3. C Switch Statement
A C switch statement allows multiple conditional branches based on the value of an expression.
<switch-statement> ::= "switch" "(" <expression> ")" "{" { <case-clause> | <default-clause> } "}"
<case-clause> ::= "case" <constant> ":" { <statement> } [ "break" ";" ]
<default-clause> ::= "default" ":" { <statement> }
<expression> ::= <identifier> | <constant> | <operation>
<constant> ::= <integer> | <char> | <string>
<statement> ::= <expression> ";" | <control-statement>
<control-statement> ::= "break" ";" | "continue" ";"
<operation> ::= <expression> "+" <expression> | <expression> "-" <expression>Explanation:
This describes a C switch statement, where an expression is evaluated, and depending on the constant values (case), different blocks of statements are executed. The default block is executed if no case matches, and break exits the switch.
4. C Union Definition
A C union allows different data types to be stored in the same memory location, but only one value at a time.
<union-definition> ::= "union" <identifier> "{" { <union-member> } "}"
<union-member> ::= <type> <identifier> ";"
<type> ::= "int" | "float" | "char" | <identifier>
<identifier> ::= <letter> { <letter> | <digit> }Explanation:
This describes a C union definition where multiple members of different types can share the same memory, but only one member can hold a value at any given time.
5. C Float Literals
A float literal in C is a numeric constant that represents a floating-point number.
<float-literal> ::= <integer> "." <digit-sequence> [ "e" [ "+" | "-" ] <digit-sequence> ]
<digit-sequence> ::= <digit> { <digit> }
<digit> ::= "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"
<integer> ::= <digit> { <digit> }Explanation:
This defines a C float literal, which consists of an integer part, a decimal point, followed by a sequence of digits. Optionally, it can have an exponent part (e.g., 1.23e10).
Final Explanation
The EBNF descriptions provided give formal rules for different language constructs in Java and C, explaining how these constructs can be structured and parsed. The main goal of EBNF is to describe the syntax of a language clearly, showing how various components (such as identifiers, expressions, and statements) combine to form valid code. By writing these rules, developers and parsers can understand the valid structures in a program and ensure that code adheres to the expected format.