2.11 Jb0150: java oop: a gentle introduction to java data types  (Page 4/9)

Can purchase integer quantities only

For example, the grocer is happy to sell me one can of applesauce and is even happier to sell me 36 cans of applesauce. However, she wouldbe very unhappy if I were to open a can of applesauce in the store and attempt to purchase 6.3 cans of applesauce.

Counting doesn't require fractional parts

A count of the number of cans of applesauce that I purchase is somewhat analogous to the concept of whole-number data types in Java. Applesauceis not available in fractional parts of cans (at my grocery store) .

Fractional pounds of hamburger are available

On the other hand, the grocer is perfectly willing to sell me 6.3 pounds of hamburger. This is somewhat analogous to floating-point data types in Java.

Accommodating applesauce and hamburger in a program

Therefore, if I were writing a program dealing with quantities of applesauce and hamburger, I might elect to use a whole number type to represent cansof applesauce and to use a floating-point type to represent pounds of hamburger.

Different whole-number types

In Java, there are four different whole-number types:

• byte
• short
• int
• long

(The char type is also a whole number type, but since it is not intended to be used for arithmetic, I discuss it later as a character type.)

The four types differ primarily in terms of the range of values that they can accommodate and the amount of computer memory required to store instancesof the types.

Differences in operations?

Although there are some subtle differences among the four whole-number types in terms of the operations that you can perform on them, I will defer a discussion of thosedifferences until a more advanced module. (For example some operations requireinstances of the byte and short types to be converted to type int before the operation takes place.)

Algebraically signed values

All four of these types can be used to represent algebraically signed values ranging from a specific negative value to a specific positive value.

Range of the byte type

For example, the byte type can be used to represent the set of whole numbers ranging from -128 to +127 inclusive. (This constitutes a set of 256 different values, including the value zero.)

The byte type cannot be used to represent any value outside this range. For example, the byte type cannot be used to represent either -129 or +128.

No fractional parts allowed by the byte type

Also, the byte type cannot be used to represent fractional values within the allowable range. For example, the byte type cannotbe used to represent the value of 63.5 or any other value that has a fractional part.

Like a strange odometer

To form a crude analogy, the byte type is sort of like a strange odometer in a new (and unusual) car that shows a mileage value of -128 when you first purchase the car. As you drive the car, the negativevalues shown on the odometer increment toward zero and then pass zero. Beyond that point they increment up toward the value of +127.

Oops, numeric overflow!

When the value passes (or attempts to pass) +127 miles, something bad happens. From that point forward, the value shown on the odometeris not a reliable indicator of the number of miles that the car has been driven.