2.11 Jb0150: java oop: a gentle introduction to java data types  (Page 3/9)

It is fairly common for an odometer to be able to store and to display the set of all positive values ranging from zero to 99999. Ifyour odometer is designed to store that set of values and if you drive your car more than 99999 miles, it is likely that the odometer willroll over and start back at zero after you pass the 99999-mile mark. In other words, that particular odometer does not have the ability tostore a value of 100,000 miles. Once you pass the 99999-mark, the data stored in the odometer is corrupt.

Now let's return to the Java type named short

Assume that you have two instances of the type short in a Java program. What are the operations that you can perform on those instances? For example:

• You can add them together.
• You can subtract one from the other.
• You can multiply one by the other.
• You can divide one by the other.
• You can compare one with the other to determine which is algebraically larger.

There are some other operations that are allowed as well. In fact, there is a well-defined set of operations that you are allowed toperform on those instances. That set of operations is defined in the specification for the type short .

What if you want to do something different?

However, if you want to perform an operation that is not allowed by the type specification, then you will have to find another way toaccomplish that purpose.

For example, some programming languages allow you to raise whole-number types to a power (examples: four squared, six cubed, nine to the fourth power, etc.) . However, that operation is not allowed by the Java specification for the type short . If you need to do that operation with a data value of the Java short type, you must find another way to do it.

Two major categories of type

Java data types can be subdivided into two major categories:

• Primitive types
• User-defined or reference types

These categories are discussed in more detail in the following sections.

Primitive types

Java is an extensible programming language

What this means is that there is a core component to the language that is always available. Beyond this, individual programmers can extendthe language to provide new capabilities. The primitive types discussed in this section are the types that are part of the core language.A later section will discuss user-defined types that become available when a programmer extends the language.

More subdivision

It seems that when teaching programming, I constantly find myself subdividing topics into sub-topics. I am going to subdivide the topic of PrimitiveTypes into four categories:

• Whole-number types
• Floating-point types
• Character types
• Boolean types

Hopefully this categorization will make it possible for me to explain these types in a way that is easier for you to understand.

Whole-number types

The whole-number types, often called integer types, are relatively easy to understand. These are types that can be used to representdata without fractional parts.

Applesauce and hamburger

For example, consider purchasing applesauce and hamburger. At the grocery store where I shop, I am allowed to purchase cans of applesauceonly in whole-number or integer quantities.