CS 480/680 Comparative Language

Wright State University
Department of Computer Science and Engineering
CS 480/680 Comparative Language

Summer 2011 Final Examination Prasad

1. Expression Translation (4 + 5 pts)
This problem is based on background material for the Java programming assignment. Consider the following template for a collection of Java programs (called Test), where <expr> can be replaced with an expression derived from the grammar shown below. Note that <expr>, <term>, and <factor> are nonterminals, while i, a, +, *, (, and ) are terminals. {} stands for Kleene star. Note also that operator precedence is implicit in the productions, and * has precedence over +.

class Test {
    static double f(double a, int i){
       return <expr>;
    }
    public static void main(String[] args){
       System.out.println(f(1,2.0));
    }
}

           <expr>   -> <term>   { + <term> }
           <term>   -> <factor> { * <factor> }
           <factor> -> i | a | ( <expr> )

The formal argument argument a is located in register 0 and i is located in register 2. The relevant JVM instructions are: dload_0, iload_2, i2d, dadd, iadd, dmul and imul. (Note that the method returns a double in the end.)
(i) Write the Java bytecode generated for the following arithmetic expression:
                 i * ( i + i ) + a
(ii) Write the Java bytecode generated for the following arithmetic expression (assuming that + is left associative and * is left associative):
                i * i + i + i * i

2. Java : Polymorphism and Dynamic Binding (1 + 5 pts)

Does the following program compile without any errors? If not, correct the program "minimally" before proceeding further.

Write the output of executing the (possibly corrected) Java program indicating any run-time exceptions it may generate. (Hint: Focus on the declared type of a variable and the class associated with the object referred to by the variable.)

class A {
String f(A x) { return (" AA ");}

       String f(B x) { return (" AB ");}
    }
    class B extends A {
       String f(A x) { return (" BA ");}

       String f(B x) { return (" BB ");}    }
    class Final {
        public static void main(String[] args) {
            A[] arr = {new A(), new B(), null};

            System.out.println(arr[0].f(arr[0]));             System.out.println(arr[1].f(arr[0]));                                System.out.println(arr[1].f(arr[1]));
            System.out.println(arr[0].f(arr[2]));
            System.out.println(arr[2].f(arr[0]));              }
    }

3. Java Concepts (5*3/3*5 pts)

Java does not permit overriding run()-method in a subclass of class java.lang.Thread to be declared private, or throw InterruptedException. Explain why?

Explain the difference between static scoping and dynamic scoping.

The inheritance of overloaded methods in Java and C++ differ in a fundamental way. Clearly show the difference in the two approaches taken and argue why Java's design decision is preferable.
(Additional problems for CS680 Students)
- Explain the benefits of supporting multi-threading in a programming language?
- What is a higher-order function?

4. Language Processing ((4 +1) + (0 + 2 + 3) pts)
Study the Java program given on the reverse side carefully and answer the following questions.

Specify the grammar for the input language in EBNF form. (Use a pair of curly braces for Kleene Star operation.) What is the associativity of '-'?

What is the result of invoking the program on the exprFinal.dat file containing the following 3 expressions.

        x
       x - y
       x - y - y

T. K. Prasad