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.
ArrayList
s 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
Suggest some methods that will be useful for Entry
.