Getting Started - Absolute Java - page 23

What Is Doubled?

How did the floating-point type double get its name? Is there another type for floating-
point numbers called “single” that is half as big? Something like that is true. There is a type
that uses half as much storage, namely the type float . Many programming languages
traditionally used two types for floating-point numbers. One type used less storage and was
very imprecise (that is, it did not allow very many significant digits). The second type used
double the amount of storage and so could be much more precise; it also allowed numbers
that were larger (although programmers tend to care more about precision than about
size). The kind of numbers that used twice as much storage were called double precision
numbers; those that used less storage were called single precision . Following this tradition,
the type that (more or less) corresponds to this double precision type in Java was named
double in Java. The type that corresponds to single precision in Java was called float .
(Actually, the type name double was inherited from C++, but this explanation applies to
why the type was named double in C++, and so ultimately it is the explanation of why the
type is called double in Java.)

Constants for strings of characters are given in double quotes, as illustrated by the
following line taken from Display 1.1 :

System.out.println("Welcome to Java.");
Be sure to notice that string constants are placed inside of double quotes, while
constants of type char are placed inside of single quotes. The two kinds of quotes
mean different things. In particular, 'A' and "A" mean different things. 'A' is a value
of type char and can be stored in a variable of type char . "A" is a string of characters.
The fact that the string happens to contain only one character does not make the string
"A" a value of type char . Also notice that, for both strings and characters, the left and
right quotes are the same. We will have more to say about strings later in this chapter.
The type boolean has two constants, true and false . These two constants may
be assigned to a variable of type boolean or used anyplace else an expression of type
boolean is allowed. They must be spelled with all lowercase letters.

quotes

Arithmetic Operators and Expressions
As in most other languages, Java allows you to form expressions using variables,
constants, and the arithmetic operators: + (addition), − (subtraction), * (multiplication),
/ (division), and % (modulo, remainder). These expressions can be used anyplace it is
legal to use a value of the type produced by the expression.
All of the arithmetic operators can be used with numbers of type int , numbers of
type double , and even with one number of each type. However, the type of the value
produced and the exact value of the result depend on the types of the numbers being

mixing types