Posted by : Rhyf Ahmad
Thursday, May 21, 2015

A variable is a named
piece of memory that you use to store information in your Java program — an
item of data of some description. Each named piece of memory that you define
can only store data of one particular type. If you define a variable to store
integers, for example, you can't use it to store a value that is a decimal
fraction, such as 0.75.

If you've defined a variable that you use to refer to
a Hat object, you can only use it to reference an object of type Hat (or any of
its subclasses, as you will see in Chapter 6). Because the type of data that
each variable can store is fixed, the compiler can verify that each variable
you define in your program is not used in a manner or a context that is
inappropriate to its type. If a method in your program is supposed to process
integers, the compiler is able to detect when you inadvertently try to use the
method with some other kind of data, for example, a string or a numerical value
that is not integral. Explicit data values that appear in your program are
called literals. Each literal is also of a particular type: 5, for example, is an integer literal of type
int. I will go into the characteristics of the various types of literals that
you can use as I discuss each variable type.

Contents:

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Contents:

**Data and Variables**

- Naming Your Variables
- Variable Names and Unicode
- Variables and Types

**Integer Data Types**

- Declaring Integer Variables

**Floating-Point Data Types**

- Floating-Point Literals
- Declaring Floating-Point Variables

**Fixing the Value of a Variable**

**Arithmetic Calculations**

- Integer Calculations
- Integer Division and Remainders
- The Increment and Decrement Operators
- Computation with Shorter Integer Types
- Errors in Integer Arithmetic
- Floating-Point Calculations
- Other Floating-Point Arithmetic Operators
- Error Conditions in Floating-Point Arithmetic
- Mixed Arithmetic Expressions
- Explicit Casting
- Automatic Type Conversions in Assignments

**The op= Operators**

**Mathematical Functions and Constants**

- Importing the Math Class Methods

**Storing Characters**

- Character Escape Sequences
- Character Arithmetic

**Bitwise Operations**

- Using the AND and OR Operators
- Using the Exclusive OR Operator
- Shift Operations
- Methods for Bitwise Operations

**Variables with a Fixed Set of Integer Values**

**Boolean Variables**

**Operator Precedence**

**Program Comments**

- Documentation Comments

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