MIDTERM ANSWERS -- SUMMER 2003

Part A

1. True.  The main method is the very first method to execute before
   any objects are created so it must be static.

2. True.  A string is an object of the String class.

3. True.  The + operator means addition in the case of number+number,
   but it means concatenation in the cases String+String, String+number,
   or number+String.  Since + associates from left to right, we have the
   following sequence:
   " " + 1 + 2 + 3 + 4 + 5 --> " 1" + 2 + 3 + 4 + 5 --> " 12" + 3 + 4 + 5
   --> " 123" + 4 + 5 --> " 1234" + 5 --> " 12345".

4. True.
   f = (!(x > y) || ((y != 7) && (x - y == 1))
     = (!(7 > 9) || ((9 != 7) && (7 - 9 == 1))
     = (!false   || (  false  &&     false   )
     =    true   ||          false
     =          true

5. False.  It will execute 5 times, printing 4 7 10 13 16.

6. False.  The init method executes only once when the applet first
   starts up.  The paint method executes every time a paint event 
   occurs, including whenever the applet is restored after being
   minimized.

Part B.

1.           t    s.charAt(x)   x     y    y > 1
         --------+-----------+-----+-----+--------
          ""          'c'       2    32     true
          "c"         'h'       7    16     true
          "ch"        'm'      12     8     true
          "chm"       'r'      17     4     true
          "chmr"      'w'      22     2     true
          "chmrw"              27     1     false

2.  public void static main(String[] args)
    {
        double miles, cm;

        miles = Double.parseDouble(JOptionPane.showInputDialog(
            "Enter distance in miles."));
        cm = 2.54 * 12 * 5280 * miles;
        System.out.println("Distance in cm is " + cm + ".");
    } 

3.  public void static main(String[] args)
    {
        String s;
        char first, x;
        int i;
        boolean flag = true;

        s = JOptionPane.showInputDialog("Enter string to check.");
        
        // Variable name cannot have length 0.
        if (s.length() == 0)
        {
            System.out.println(false);
            System.exit(0);
        }

        // Variable name must start with a lower case letter.
        first = s.charAt(0);
        if (!('a' <= first && first <= 'z'))
        {
            System.out.println(false);
            System.exit(0);
        }

        // Quit if variable name consists of only a single letter.
        if (s.length() == 1)
        {
            System.out.println(true);
            System.exit(0);
        }

        // Remaining characters must be digits or letters.
        for(i = 2; i < s.length(); i++)
        if (!('a' <= first && first <= 'z') ||
            !('A' <= first && first <= 'Z') ||
            !('0' <= first && first <= '9'))
                flag = false;

        System.out.println(flag);
    }

4. See link to image.