Floating-Point Types
Floating-Point Types
Floating-point numbers, also known as real numbers, are used when evaluating expressionsthat require fractional precision. For example, calculations such as square root, ortranscendentals
such as sine and cosine, result in a value whose precision requires a floating-point type. Java
implements the standard (IEEE–754) set of floating-point types and operators. There are two
kinds of floating-point types, float and double, which represent single- and double-precision
numbers, respectively. Their width and ranges are shown here:
Name Width in Bits Approximate Range
double 64 4.9e–324 to 1.8e+308
float 32 1.4e–045 to 3.4e+038
float
The type float specifies a single-precision value that uses 32 bits of storage. Single precision isfaster on some processors and takes half as much space as double precision, but will become
imprecise when the values are either very large or very small. Variables of type float are useful
when you need a fractional component, but don’t require a large degree of precision. For
example, float can be useful when representing dollars and cents.
Here are some example float variable declarations:
float hightemp, lowtemp;
double
Double precision, as denoted by the double keyword, uses 64 bits to store a value. Doubleprecision is actually faster than single precision on some modern processors that have been
optimized for high-speed mathematical calculations. All transcendental math functions, such
as sin( ), cos( ), and sqrt( ), return double values. When you need to maintain accuracy overmany iterative calculations, or are manipulating large-valued numbers, double is the best
choice.
Here is a short program that uses double variables to compute the area of a circle:
// Compute the area of a circle.
class Area {
public static void main(String args[]) {
double pi, r, a;
r = 10.8; // radius of circle
pi = 3.1416; // pi, approximately
a = pi * r * r; // compute area
System.out.println("Area of circle is " + a);
}
}
Characters
In Java, the data type used to store characters is char. However, C/C++ programmers beware:char in Java is not the same as char in C or C++. In C/C++, char is 8 bits wide. This is not the
case in Java. Instead, Java uses Unicode to represent characters. Unicode defines a fully
international character set that can represent all of the characters found in all human
languages. It is a unification of dozens of character sets, such as Latin, Greek, Arabic, Cyrillic,
Hebrew, Katakana, Hangul, and many more. For this purpose, it requires 16 bits. Thus, in
Java char is a 16-bit type. The range of a char is 0 to 65,536. There are no negative chars.
The standard set of characters known as ASCII still ranges from 0 to 127 as always, and the
extended 8-bit character set, ISO-Latin-1, ranges from 0 to 255. Since Java is designed to
allow programs to be written for worldwide use, it makes sense that it would use Unicode to
represent characters. Of course, the use of Unicode is somewhat inefficient for languages such
as English, German, Spanish, or French, whose characters can easily be contained within 8 bits.
But such is the price that must be paid for global portability.
NOTE More information about Unicode can be found at http://www.unicode.org.
Here is a program that demonstrates char variables:// Demonstrate char data type.
class CharDemo {
public static void main(String args[]) {
char ch1, ch2;
ch1 = 88; // code for X
ch2 = 'Y';
System.out.print("ch1 and ch2: ");
System.out.println(ch1 + " " + ch2);
}
}
This program displays the following output:
ch1 and ch2: X Y
Notice that ch1 is assigned the value 88, which is the ASCII (and Unicode) value that
corresponds to the letter X. As mentioned, the ASCII character set occupies the first 127
values in the Unicode character set. For this reason, all the “old tricks” that you may have
used with characters in other languages will work in Java, too.
Although char is designed to hold Unicode characters, it can also be thought of as an
integer type on which you can perform arithmetic operations. For example, you can add
two characters together, or increment the value of a character variable. Consider the
following program:
// char variables behave like integers.
class CharDemo2 {
public static void main(String args[]) {
char ch1;
ch1 = 'X';
System.out.println("ch1 contains " + ch1);
ch1++; // increment ch1
System.out.println("ch1 is now " + ch1);
}
}
The output generated by this program is shown here:
ch1 contains X
ch1 is now Y
In the program, ch1 is first given the value X. Next, ch1 is incremented. This results in ch1
containing Y, the next character in the ASCII (and Unicode) sequence.
Booleans
Java has a primitive type, called boolean, for logical values. It can have only one of two
possible values, true or false. This is the type returned by all relational operators, as in the
case of a < b. boolean is also the type required by the conditional expressions that govern
the control statements such as if and for.
Here is a program that demonstrates the boolean type:
// Demonstrate boolean values.
class BoolTest {
public static void main(String args[]) {
boolean b;
b = false;
System.out.println("b is " + b);
b = true;
System.out.println("b is " + b);
// a boolean value can control the if statement
if(b) System.out.println("This is executed.");
b = false;
if(b) System.out.println("This is not executed.");
// outcome of a relational operator is a boolean value
System.out.println("10 > 9 is " + (10 > 9));
}
}
The output generated by this program is shown here:
b is false
b is true
This is executed.
10 > 9 is true
There are three interesting things to notice about this program. First, as you can see, when
a boolean value is output by println( ), “true” or “false” is displayed. Second, the value of a
boolean variable is sufficient, by itself, to control the if statement. There is no need to write
an if statement like this:
if(b == true) ...
Third, the outcome of a relational operator, such as <, is a boolean value. This is why the
expression 10 > 9 displays the value “true.” Further, the extra set of parentheses around 10 > 9
is necessary because the + operator has a higher precedence than the >.
A Closer Look at Literals
Literals were mentioned briefly in Chapter 2. Now that the built-in types have been formally
described, let’s take a closer look at them.
Integer Literals
Integers are probably the most commonly used type in the typical program. Any whole
number value is an integer literal. Examples are 1, 2, 3, and 42. These are all decimal values,
meaning they are describing a base 10 number. There are two other bases which can be used
in integer literals, octal (base eight) and hexadecimal (base 16). Octal values are denoted in Java
by a leading zero. Normal decimal numbers cannot have a leading zero. Thus, the seemingly
valid value 09 will produce an error from the compiler, since 9 is outside of octal’s 0 to 7 range.
A more common base for numbers used by programmers is hexadecimal, which matches
cleanly with modulo 8 word sizes, such as 8, 16, 32, and 64 bits. You signify a hexadecimal
constant with a leading zero-x, (0x or 0X). The range of a hexadecimal digit is 0 to 15, so A
through F (or a through f ) are substituted for 10 through 15.
Integer literals create an int value, which in Java is a 32-bit integer value. Since Java is
strongly typed, you might be wondering how it is possible to assign an integer literal to one
of Java’s other integer types, such as byte or long, without causing a type mismatch error.
Fortunately, such situations are easily handled. When a literal value is assigned to a byte or
short variable, no error is generated if the literal value is within the range of the target type.An integer literal can always be assigned to a long variable. However, to specify a long
literal, you will need to explicitly tell the compiler that the literal value is of type long. You
do this by appending an upper- or lowercase L to the literal. For example, 0x7ffffffffffffffL
or 9223372036854775807L is the largest long. An integer can also be assigned to a char as
long as it is within range.
Floating-Point Literals
Floating-point numbers represent decimal values with a fractional component. They can beexpressed in either standard or scientific notation. Standard notation consists of a whole number
component followed by a decimal point followed by a fractional component. For example, 2.0,
3.14159, and 0.6667 represent valid standard-notation floating-point numbers. Scientific notation
uses a standard-notation, floating-point number plus a suffix that specifies a power of 10 by
which the number is to be multiplied. The exponent is indicated by an E or e followed by a
decimal number, which can be positive or negative. Examples include 6.022E23, 314159E–05,
and 2e+100.
Floating-point literals in Java default to double precision. To specify a float literal, you
must append an F or f to the constant. You can also explicitly specify a double literal by
appending a D or d. Doing so is, of course, redundant. The default double type consumes 64
bits of storage, while the less-accurate float type requires only 32 bits.
Boolean Literals
Boolean literals are simple. There are only two logical values that a boolean value can have,true and false. The values of true and false do not convert into any numerical representation.
The true literal in Java does not equal 1, nor does the false literal equal 0. In Java, they can only
be assigned to variables declared as boolean, or used in expressions with Boolean operators.
Character Literals
Characters in Java are indices into the Unicode character set. They are 16-bit values that canbe converted into integers and manipulated with the integer operators, such as the addition
and subtraction operators. A literal character is represented inside a pair of single quotes. All
of the visible ASCII characters can be directly entered inside the quotes, such as ‘a’, ‘z’, and ‘@’.
For characters that are impossible to enter directly, there are several escape sequences that allow
you to enter the character you need, such as ‘\’’ for the single-quote character itself and ‘\n’for
the newline character. There is also a mechanism for directly entering the value of a character in
octal or hexadecimal. For octal notation, use the backslash followed by the three-digit
number. For example, ‘\141’ is the letter ‘a’. For hexadecimal, you enter a backslash-u (\u), then
exactly four hexadecimal digits. For example, ‘\u0061’is the ISO-Latin-1 ‘a’ because the top byte
is zero. ‘\ua432’is a Japanese Katakana character. Table 3-1 shows the character escape sequences.
String Literals
String literals in Java are specified like they are in most other languages—by enclosinga sequence of characters between a pair of double quotes. Examples of string literals are
“Hello World”
“two\nlines”
“\”This is in quotes\”“
The escape sequences and octal/hexadecimal notations that were defined for character
literals work the same way inside of string literals. One important thing to note about Java
strings is that they must begin and end on the same line. There is no line-continuation escape
sequence as there is in some other languages.
NOTE As you may know, in some other languages, including C/C++, strings are implemented as
arrays of characters. However, this is not the case in Java. Strings are actually object types. As
you will see later in this book, because Java implements strings as objects, Java includes extensive
string-handling capabilities that are both powerful and easy to use.
Post author : Narayana KNR.
Book author : Herbert Schildt.
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