Section 3.3. Data Types in Java

   

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3.3 Data Types in Java

Java uses different types to store data; it is thus referred to as a strongly typed language. The range of values for these types is based on the number 2 raised to a power equal to the number of bits for each type. An 8-bit number therefore has 2 ⁸ possible values, or 256 values. You may have used a bit data type in an SQL database to represent a value such as isOnSpecial where 0 means the item is not currently on special, and 1 means it is. Since 2 ¹ = 2, we see that a 1-bit number (bit) has a range of possible values of 2 ”it can be 0 or 1.

However, when determining the range of possible values for a data type in Java, one of the bits in the result is saved to represent the number's sign (whether it is positive or negative). Therefore, an 8-bit number does not represent the 256 values 0 to 255. It represents the values “128 to +127. The highest value possible for an 8-bit number is going to be 2 to the power of the number of bits minus 1, minus 1. For an 8-bit number, this is represented 2 ^{8 “1} “1, or 2 ⁷ “1. So, 2 ⁷ is 128, minus 1 is 127. It is necessary to subtract the 1 because zero is counted as positive. This is an important aspect of working with Java that can be hard to remember at first: things generally start at 0, not 1.

You can use this formula to calculate the range of possible values for a given data type: ( “2 ^{x “1 to} 2 ^{x “1} “1).

As mentioned above, Java has predefined data types that allow for only certain values to be stored in them (such as numeric or character values), and those data types have a predefined range expressed in a number of bits, of values they are capable of holding. Different kinds of information are stored in different data types in Java.

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