Variables

A variable is a name that has a value. A variable can have different values at different times.

All variables must be declared. When a variable is declared, it is given a type that tells what kind of values it can have. It may also be given an initial value. An int variable can only have an integer value, a String variable can only have a character string as its value, and so on.

Java is case-sensitive; that is, result, Result, and RESULT are three different variables. Type names must be capitalized correctly: int, not Int; String, not string; etc.

• An instance variable is one that is declared in a class but a separate copy of it is "owned" by each individual instance, or object, of that class.
• A class variable, or static variable, is declared in a class using the keyword static. There is only one of it, and it is considered to be "owned" by the class itself, not by individual objects.
• A local variable is one that is declared within a method. It is available only within that method.

There are strict conventions for variable names:

• Names are almost never abbreviated: Use employee rather than emp; use yearEndBonus rather than yebonus. (However, very common abbreviations can be used, such as max and min.)
• Variable names always begin with a lowercase letter.
• If a name consists of multiple words, the first letter of all words except the first is capitalized, for example, endOfLineMarker, totalBill. (This is sometimes called "camelCase.")
• Although legal, variable names never contain the underscore (unless they are constants) or the dollar sign.