Data types

                        Data Types

Java Is a Strongly Typed Language

It is important to state at the outset that Java is a strongly typed language. Indeed, part of
Java’s safety and robustness comes from this fact. Let’s see what this means. First, every
variable has a type, every expression has a type, and every type is strictly defined. Second,
all assignments, whether explicit or via parameter passing in method calls, are checked for
type compatibility. There are no automatic coercions or conversions of conflicting types as
in some languages. The Java compiler checks all expressions and parameters to ensure that
the types are compatible. Any type mismatches are errors that must be corrected before the
compiler will finish compiling the class.

The Primitive Types

Java defines eight primitive types of data: byte, short, int, long, char, float, double, and boolean.
The primitive types are also commonly referred to as simple types, and both terms will be
used in this book. These can be put in four groups:
•  Integers This group includes byte, short, int, and long, which are for whole-valued
signed numbers.
•  Floating-point numbers This group includes float and double, which represent
numbers with fractional precision.
•  Characters This group includes char, which represents symbols in a character set,
like letters and numbers.
• Boolean This group includes boolean, which is a special type for representing
true/false values.

You can use these types as-is, or to construct arrays or your own class types. Thus, they
form the basis for all other types of data that you can create.

The primitive types represent single values—not complex objects. Although Java is
otherwise completely object-oriented, the primitive types are not. They are analogous to
the simple types found in most other non–object-oriented languages. The reason for this is
efficiency. Making the primitive types into objects would have degraded performance too much.
The primitive types are defined to have an explicit range and mathematical behavior.
Languages such as C and C++ allow the size of an integer to vary based upon the dictates
of the execution environment. However, Java is different. Because of Java’s portability
requirement, all data types have a strictly defined range. For example, an int is always 32 bits,
regardless of the particular platform. This allows programs to be written that are guaranteed
to run without porting on any machine architecture. While strictly specifying the size of an
integer may cause a small loss of performance in some environments, it is necessary in order
to achieve portability.
Let’s look at each type of data in turn.

Integers

Java defines four integer types: byte, short, int, and long. All of these are signed, positive
and negative values. Java does not support unsigned, positive-only integers. Many other
computer languages support both signed and unsigned integers. However, Java’s designers
felt that unsigned integers were unnecessary. Specifically, they felt that the concept of unsigned
was used mostly to specify the behavior of the high-order bit, which defines the sign of an integer
value. As you will see in Chapter 4, Java manages the meaning of the high-order bit differently,
by adding a special “unsigned right shift” operator. Thus, the need for an unsigned integer type
was eliminated.
The width of an integer type should not be thought of as the amount of storage it consumes,
but rather as the behavior it defines for variables and expressions of that type. The Java run-time
environment is free to use whatever size it wants, as long as the types behave as you declared
them. The width and ranges of these integer types vary widely, as shown in this table:

byte

The smallest integer type is byte. This is a signed 8-bit type that has a range from –128 to 127.
Variables of type byte are especially useful when you’re working with a stream of data from
a network or file. They are also useful when you’re working with raw binary data that may
not be directly compatible with Java’s other built-in types.
Byte variables are declared by use of the byte keyword. For example, the following
declares two byte variables called b and c:
byte b, c;

short

short is a signed 16-bit type. It has a range from –32,768 to 32,767. It is probably the least-used
Java type. Here are some examples of short variable declarations:
short s;
short t;

int

The most commonly used integer type is int. It is a signed 32-bit type that has a range
from –2,147,483,648 to 2,147,483,647. In addition to other uses, variables of type int are
commonly employed to control loops and to index arrays. Although you might think that
using a byte or short would be more efficient than using an int in situations in which the
larger range of an int is not needed, this may not be the case. The reason is that when byte
and short values are used in an expression they are promoted to int when the expression is
evaluated. (Type promotion is described later in this chapter.) Therefore, int is often the best
choice when an integer is needed.

long

long is a signed 64-bit type and is useful for those occasions where an int type is not large
enough to hold the desired value. The range of a long is quite large. This makes it useful
when big, whole numbers are needed. For example, here is a program that computes the
number of miles that light will travel in a specified number of days.
// Compute distance light travels using long variables.
class Light {
public static void main(String args[]) {
int lightspeed;
long days;
long seconds;
long distance;
// approximate speed of light in miles per second
lightspeed = 186000;
days = 1000; // specify number of days here
seconds = days * 24 * 60 * 60; // convert to seconds
distance = lightspeed * seconds; // compute distance
System.out.print("In " + days);
System.out.print(" days light will travel about ");
System.out.println(distance + " miles.");
}
}
This program generates the following
  output:
In 1000 days light will travel about 16070400000000 miles.
Clearly, the result could not have been held in an int variable.
      Click on link to run program get output :https://goo.gl/qzfd3B

          Post author: Narayana KNR.
          Book author : Herbert Schildt.
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