The Java Lesson 3: Identifiers and primitive data types

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1. Identifiers in Java | 2. Primitive data types in Java

Identifiers and primitive data types

Uses of identifiers

• To name a variable (a data area that takes on different values during processing)

• To name a method (a module of code)

• To name a class (a definition from which objects can be constructed)

• To label a statement (for later referencing)

Rules for identifiers

• It must not be a Java keyword

• It must begin with a letter, dollar sign ( $ ), or underscore ( _ )

• Subsequent characters may be letters, dollar signs, underscores, or digits

• Case matters. For example, the three identifiers MAIN, Main, and main are different.

Examples of valid identifiers

yearlyGrossPay

_2002_Budget

JuneActual

$totalAmtDue

Programming conventions

• Are not enforced by the compiler but make it easier to read and maintain Java code

• Most programmers use "camel caps" (such as firstQuarterSalesTotal) to handle long identifiers that appear to contain multiple words. Some use undercores (like first_Quarter_Sales_Totals).

• Begin variable names, method names, and labels with a lower case letter. For example, totalAmount, hoursWorked, employeeName, calcBonus, and main.

• Begin class names with a capital letter. For example, Person, Customer, SalesRep, and Part.

• Names of constants should be all capitals. For example, TAX_RATE, COMMISSION, and DEPOSIT_CODE.

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