CIS1068
Spring 2010
                              MIDTERM 2 

Closed books, closed notes.
The points per question are indicated next to the question.
The total points for the exam are 175.

(5)   1. What is a stub? How does it help us?










(5)   2. Give an example of 
	 (a) an instance method
	 (b) a static method













(10)   3. True/False questions
	(a) The value of a local variable named x has no direct relationship
	    with the value of a variable named x in the caller
	(b) Assigning a new value to a parameter changes the value of the 
	    corresponding variable in the caller's argument list
	(c) Local int variables are automatically initialized to 0
	(d) Instance String data members are automatically initialized to 0.
	(e) Instance methods cannot access static data members




(10)  4. Multiple choice:
	i.  What is an algorithm?
	     a. An unambiguous specification of a way to solve a problem.
      	     b. A Java program.
      	     c. An organization of several memory cells into a coherent structure.
             d. A data type that includes specifications for both procedures and data.
	ii. Which of the following best defines the scope of a variable?
      	     a. The type of values that may be stored in the variable.
      	     b. The part of a program where the variable can be legally accessed.
      	     c. The largest value that can be stored in the variable.
      	     d. The value currently stored in a variable.



(10)  5. Here are some assignments. Indicate if they are correct
	 and, if wrong, correct them (don't change the type of variables):
	(a)	int x = 3.4;
	(b)	Integer v = 12;
	(c)     int k = v;
	(d)	double z = k;
	(e)	float w = z;
	(f)	int u = 'x';






(15)  6. This program does not do anything useful.
	 Its aim is to test your ability to trace a program.
	 public class aaa {
	     public static void main(String[] args) {
		bbb(13);
	     }
	     private void bbb(int x) {
		int y = 0;
		for (int k = 1; k < x; k *= 2)
			y = ccc(y, k);
		System.out.println("bbb: x = " + x + ", y = " + y);
	     }
	     private int ccc(int x, int y) {
		x = 10*x+y;
		System.out.println("ccc: x = " + x + ", y = " + y);
		return x;
	     }
	}






















(10)  7. Define the Fraction class. Show the data members, a constructor,
	 an accessor method and a setter method.




















(10)  8. What is the value of the expression below
         (show all the steps used in evaluating this
         expression):
           (5 > 4 + 3 / 2 * 2) || ( 3 % 2 != 3) && 1 < 3















(10) 9. Given the following method moo:
            static void moo(int[] a) {
		for (int k = 0; k < a.length; k++) {
			int temp = a[k];
			a[k] = a[a.length-k-1];
			a[a.length-k-1] = temp;
		}
            }
	 Given int[] joe = {1,2,3,4,5,6,7} what is the value of joe after 
	 the call moo(joe). More in general what is the purpose of this method.










(10)10. After the statement "int[][] m = {{1,2,3},{4,5,6,7}}; is executed
         specify the value of each of the following expressions:
          m[1] =
          m.length =
          m[0][m[0].length-2] =
          m[3][3] =
          m[0].length + m[1].length =








(15) 11. Write a static method minVal that returns the smallest value
         found in a two dimensional array of integers. You may assume no 
	 array is null or empty.
	 
















(15) 12. Implement the method
            public static String squeeze(String s, String v);
         which returns the string consisting of all the characters of s
	 that do not occur in v. For example squeeze("rosanna", "ram")
	 is "osnn".
















(5)  13. This is also a continuation of question 12.
	 State a precondition for the method squeeze.









(10) 14. Consider the following method:
   		public static void mystery(String [] arr) {
   		     for(int i=1; i < arr.length; i++) {
             		arr[i] = arr[i-1] + arr[i];
        	     }
   		}
   	a. What is the approximate run time of the mystery method in terms of the
   	   length of the input array?
   	b. What is the content of the array a = {"roses", "are", "red"}; 
	   after the call mistery(a)?












(20) 15. Complete all methods below for the class Foo
	public class Foo {
	    private int[] a;

	    // constructor with given length for a
	    public Foo(int length) {
		
	    }

	    // accessor returning the length of a
	    public int length() {

	    }

	    // accessor, return the element at position j in a
	    public int elementAt(int j) {

	    }

	    // modifier/setter, set element at position j in a to v
	    public void setElementAt(int j, int v) {

	    }

	    // Equal test, returns true if 2 Foo are same reference
	    public boolean identical(Foo b) {


	    }

	    // Equivalence test, returns true if 2 Foo have same content
	    public boolean equals(Foo b) {



	    }

         }









(15) 16. Write a static method isPowerOf2 that, applied to a positive
         integer n, returns true if and only if n is a power of 2.