Introduction to Classes, Objects, Methods and Strings - Java: How to Program Early Objects - page 84

There's No Default Constructor in a Class That Declares a Constructor
If you declare a constructor for a class, the compiler will not create a default constructor for
that class. In that case, you will not be able to create an Account object with the class in-
stance creation expression new Account() as we did in Fig. 3.2—unless the custom con-
structor you declare takes no parameters.
Software Engineering Observation 3.3
Unless default initialization of your class's instance variables is acceptable, provide a
custom constructor to ensure that your instance variables are properly initialized with
meaningful values when each new object of your class is created.
Adding the Constructor to Class Account 's UML Class Diagram
The UML class diagram of Fig. 3.7 models class Account of Fig. 3.5, which has a construc-
tor with a String name parameter. Like operations, the UML models constructors in the
third compartment of a class diagram. To distinguish a constructor from the class's oper-
ations, the UML requires that the word “constructor” be enclosed in guillemets (« and »)
and placed before the constructor's name. It's customary to list constructors before other
operations in the third compartment.
Account
- name : String
«constructor» Account(name: String)
+ setName(name: String)
+ getName() : String
Fig. 3.7 | UML class diagram for Account class of Fig. 3.5.
3.5 Account Class with a Balance; Floating-Point
Numbers
We now declare an Account class that maintains the balance of a bank account in addition
to the name. Most account balances are not integers. So, class Account represents the ac-
count balance as a floating-point number —a number with a decimal point , such as 43.95,
0.0, -129.8873. [In Chapter 8, we'll begin representing monetary amounts precisely with
class BigDecimal as you should do when writing industrial-strength monetary applications.]
Java provides two primitive types for storing floating-point numbers in memory—
float and double . Variables of type float represent single-precision floating-point num-
bers and can hold up to seven significant digits . Variables of type double represent double-
precision floating-point numbers . These require twice as much memory as float variables
and can hold up to 15 significant digits —about double the precision of float variables.
Most programmers represent floating-point numbers with type double . In fact, Java
treats all floating-point numbers you type in a program's source code (such as 7.33 and
0.0975) as double values by default. Such values in the source code are known as floating-
point literals . See Appendix D, Primitive Types, for the precise ranges of values for float s
and double s.