Integers

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, including C/C++, 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 defined the sign of an int when expressed as a number. 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. In fact, at least one implementation stores bytes and shorts as 32-bit (rather than 8- and 16-bit) values to improve performance, because that is the word size of most computers currently in use.

The width and ranges of these integer types vary widely, as shown in this table:

Name Width Range

long 64 9,223,372,036,854,775,808 to 9,223,372,036,854,775,807

int 32 2,147,483,648 to 2,147,483,647

short 16 32,768 to 32,767

byte 8 128 to 127

THE

JAVA

LANGUAGE

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.

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. Any time you have an integer expression involving bytes, shorts, ints, and literal numbers, the entire expression is promoted to int before the calculation is done.

The int type is the most versatile and efficient type, and it should be used most of

the time when you want to create a number for counting or indexing arrays or doing

integer math. It may seem that using short or byte will save space, but there is no

guarantee that Java won’t promote those types to int internally anyway. Remember,

type determines behavior, not size. (The only exception is arrays, where byte is

guaranteed to use only one byte per array element, short will use two bytes, and int

will use four.)

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, since it is defined as having its high byte first (called big-endian

format). This type is mostly applicable to 16-bit computers, which are becoming

increasingly scarce.

Here are some examples of short variable declarations:

short s;

short t;

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;