By: Abinaya in Java Tutorials on 2007-10-13The Java programming language is strongly-typed, which means that all variables must first be declared before they can be used. This involves stating the variable's type and name, as you've already seen:
Doing so tells your program that a field named "gear" exists, holds numerical data, and has an initial value of "1". A variable's data type determines the values it may contain, plus the operations that may be performed on it. In addition toint gear = 1;
int, the Java programming
language supports seven other primitive data types. A primitive type is
predefined by the language and is named by a reserved keyword. Primitive
values do not share state with other primitive values. The eight primitive
data types supported by the Java programming language are:
- byte: The
bytedata type is an 8-bit signed two's complement integer. It has a minimum value of -128 and a maximum value of 127 (inclusive). The
bytedata type can be useful for saving memory in large arrays, where the memory savings actually matters. They can also be used in place of
intwhere their limits help to clarify your code; the fact that a variable's range is limited can serve as a form of documentation.
- short: The
shortdata type is a 16-bit signed two's complement integer. It has a minimum value of -32,768 and a maximum value of 32,767 (inclusive). As with
byte, the same guidelines apply: you can use a
shortto save memory in large arrays, in situations where the memory savings actually matters.
- int: The
intdata type is a 32-bit signed two's complement integer. It has a minimum value of -2,147,483,648 and a maximum value of 2,147,483,647 (inclusive). For integral values, this data type is generally the default choice unless there is a reason (like the above) to choose something else. This data type will most likely be large enough for the numbers your program will use, but if you need a wider range of values, use
- long: The
longdata type is a 64-bit signed two's complement integer. It has a minimum value of -9,223,372,036,854,775,808 and a maximum value of 9,223,372,036,854,775,807 (inclusive). Use this data type when you need a range of values wider than those provided by
- float: The
floatdata type is a single-precision 32-bit IEEE 754 floating point. Its range of values is beyond the scope of this discussion. As with the recommendations for
short, use a
double) if you need to save memory in large arrays of floating point numbers. This data type should never be used for precise values, such as currency. For that, you will need to use the java.math.BigDecimal class instead. Numbers and Strings covers
BigDecimaland other useful classes provided by the Java platform.
- double: The
doubledata type is a double-precision 64-bit IEEE 754 floating point. Its range of values is beyond the scope of this discussion. For decimal values, this data type is generally the default choice. As mentioned above, this data type should never be used for precise values, such as currency.
- boolean: The
booleandata type has only two possible values:
false. Use this data type for simple flags that track true/false conditions. This data type represents one bit of information, but its "size" isn't something that's precisely defined.
- char: The
chardata type is a single 16-bit Unicode character. It has a minimum value of
'\u0000'(or 0) and a maximum value of
'\uffff'(or 65,535 inclusive).
String object; for example,
String s =
"this is a string";.
String objects are immutable,
which means that once created, their values cannot be changed. The
class is not technically a primitive data type, but considering the special
support given to it by the language, you'll probably tend to think of it as
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