Question

1. Suppose that the integer variables n and m have been initialized. Check all the correct statements about the following code fragment.

String s2 = (n>=m) ? "one" : ( (m<=2*n) ? "two": "three" );

Question 5 options:

	If m is strictly greater than 2n then the value of s2 is "two"
	If n is equal to m then the value of s2 is "two"
	If m is strictly greater than 2n then the value of s2 is "three"
	If m is not zero and is equal to 2n, then the value of s2 is "two"

2. Suppose that our Java program is in a package consisting of the classes Utilities, House, and Main, and the class Main contains the main method of the program. Suppose further that class House has a default constructor.

Check below all the correct statements.

Question 6 options:

	If class House defines no constructors, then the main method can use the following statement House hers = new House(2500.30, 5000.50);
	If class House has the public accessor method getArea() that returns double, then it is legal to have the following statements in the main method House mine = new House(); System.out.printf("House area: %.f2\n", mine.getArea());
	If class Utilities has the public static String variable mainOffice then it is legal to have the following statement in some method of the class House System.out.printf("Main office: %s", Utilities.mainOffice);
	If class House has the private instance variable price of type double, then it is legal to have the following statements in the main method House mine = new House(); int total = (int)mine.price;

3.

A balanced brackets string (BBS) is one of the following:
1. the string {}
2. the string {b}, if b is a BBS
For example, {}, {{}} are valid BBSs, but }{, {}}, {3} are invalid BBSs. The empty string is also an invalid BBS.
Select below the one method that correctly implements recursively whether a given string s is a valid BBS.

Question 10 options:

	public static boolean isBBS(String s) { if (s.equals("{}")) return true; int l = s.length(); if (l<2) return false; if (s.charAt(0)!='{' || s.charAt(l-1)!='}') return false; return true; }
	public static boolean isBBS(String s) { int l = s.length(); if (l<2) return false; if (s.equals("{}")) return true; if (s.charAt(0)=='{' && s.charAt(l-1)=='}') return isBBS(s.substring(1, l-1)); return false; }
	public static boolean isBBS(String s) { if (s.equals("")) return false;   int l = s.length(); if (s.charAt(0)=='{' && s.charAt(l-1)=='}') return isBBS(s.substring(1, l-1)); return false; }
	public static boolean isBBS(String s) { int l = s.length(); if (l<2) return false; if (s.charAt(0)=='{' && s.charAt(l-1)=='}') return isBBS(s.substring(1, l-1)); return false; }

Answer 1

1)

The correct answers are:

• If m is strictly greater than 2n then the value of s2 is "three"
• If m is not zero and is equal to 2n, then the value of s2 is "two"

2)

The correct answers are:

• If class Utilities has the public static String variable mainOffice then it is legal to have the following statement in some method of the class House System.out.printf("Main office: %s", Utilities.mainOffice);

3)

The correct code is:

public static boolean isBBS(String s) {
int l = s.length();
if (l<2) return false;
if (s.equals("{}")) return true;
if (s.charAt(0)=='{' && s.charAt(l-1)=='}')
return isBBS(s.substring(1, l-1));
return false;
}