Answer:

The program fragment works.

Double total, meal, tax;

meal = 20.00;          // autobox the 20.0
tax  = meal*0.12;      // unbox meal, do the math, autobox the product
total = meal+tax;      // unbox meal and tax, do the math, autobox the total

System.out.println("Total Cost: " + total );   // unbox total, convert to String, concatenate

Even though this works, it is not sensible code. There is no reason to use the Double wrapper class here.

Phone Book Application

ArrayLists are especially convenient when you want to maintain a list of your own object types. For example, say that you want an application that maintains a phone book. Each entry in the phone book contains a name and a number along with various methods.

class Entry
{
  private String name;
  private String number;

  // constructor
  public Entry( String n, String num )
  {
    name = n; number = num;
  }

  // various methods
  . . .
}

The program will maintain an ArrayList of phone book entries. The user will type in a name and get a phone number.

Enter name --> Hal
Name: Hal; Number: 789-1234

Enter name --> Amy
Name: Amy; Number: 123-4567

Enter name --> quit

Answer:

Phone Book Application

QUESTION 22: