Quiz 4 Solution

Terms and Concepts

(a)
A String object is immutable (i.e. it can't be changed).
A StringBuffer object is mutable (i.e. it can be changed).

str1 == str2 compares the addresses of str1 and str2; it returns true only if str1 and str2 are referring to the same object.
str1.equals(str2) compares the contents of str1 and str2; it returns true only if str1 and str2 contain the same characters (in the same order).

(b)
1. primitive
2. reference
3. address (also acceptable: reference, memory location)

Code Tracing

student18:20
student18:16
student18:14
student14:14
student12:14
student12:12

Code Writing (code in green was given)

public void runningBalance(MainWindow mw) {
   InputBox in = new InputBox(mw);
   OutputBox out = new OutputBox(mw);
   int balance = in.getInteger("Enter the initial balance:");

   out.show();
   String ans;
   int amount;
   boolean again = true;

   do {
      ans = in.getString("Deposit (d), withdraw (w), or quit (q)?");
      switch (ans.charAt(0)) {

         case 'd':
         case 'D':
            amount = in.getInteger("How much do you want to deposit?");
            if (amount < 0)
               out.printLine("Cannot deposit negative amount");
            else {
               balance += amount;
               out.printLine("Current balance: " + balance);
            }
            break;

         case 'w':
         case 'W':
            amount = in.getInteger("How much do you want to withdraw?");
            if (amount < 0)
               out.printLine("Cannot withdraw negative amount");
            else {
               balance -= amount;
               out.printLine("Current balance: " + balance);
            }
            break;

         case 'q':
         case 'Q':
            out.printLine("Final balance: " + balance);
            again = false;

         default:
            out.printLine("Please enter d, w, or q");

      } // end switch
   } while (again);	
} // end method runningBalance