Outline Character Strings Variables and Assignment Primitive Data Types Expressions Data Conversion Interactive Programs Graphics Applets Drawing Shapes

Variables and assignment Variable A name for a location in memory holding data value Every variable has a type It depends on the intended use Example:  use the int type for a variable storing integer values A variable declaration => reserve portion of memory large enough to hold the value

Variable declaration A variable must be declared before using it by specifying The variable’s name And the type of information that it will hold int total; int count, temp, result; Multiple variables can be created in one declaration data type variable name

Variables and assignment: general rules A variable can be given an initial value in the declaration When a variable is referenced in a program, its current value is used You can change the value of an existing variable Using the assignment operator (=) lucky_number=13; (if the variable has been declared) See PianoKeys.java int sum = 0; int base = 32, max = 149;

Assignment An assignment statement Changes the value of a variable The assignment operator is the = sign The expression on the right is evaluated And the result is stored in the variable on the left The value that was in total is overwritten See Geometry.java total = 55;

Sample programs /* Input: Geometry.JAVA */ public class Geometry { public static void main (String[ ] args) { int sides = 5; // declaration with intialization System.out.println(“ A pentagon has ”+ sides + “sides.”); sides = 10; // assignment statement System.out.println(“A decagon has ” + sides + “sides.”); } // Output: A pentagon has 5 sides A decagon has 10 sides

Constants A constant is an identifier that is similar to a variable except that it holds the same value During its entire existence By giving the value a name => explain role in program is named using uppercase letters To distinguish them from regular variables In Java, we use the final modifier to declare a variable final int MIN_HEIGHT = 69;

Constants (cont’d) The compiler Produces an error message if you attempt to change the value of a constant This prevents coding errors Because the only valid place to change their value is the initial assignment

Why to use constants? Three reasons for using constants Giving a constant a value a name helps explain its role Give meaning to otherwise unclear values  For example, MAX_LOAD means more than the literal 250 Compiler protects constant values Avoid inadvertent errors by other programmers Prevent changing a constant value throughout a program They facilitate program maintenance If a constant is used in multiple places Its value need only be updated in one place

Outline Character Strings Variables and Assignment Primitive Data Types Expressions Data Conversion Interactive Programs Graphics Applets Drawing Shapes

Outline Character Strings Variables and Assignment Primitive Data Types Expressions Data Conversion Interactive Programs Graphics Applets Drawing Shapes

Primitive data types There are eight primitive data types in Java Four of them represent integers byte, short, int, long Two of them represents floating point numbers float, double One of them represents characters char And one of them represent Boolean values boolean

JAVA Primitive data types All the numeric types differ By the amount of memory space used To store a value of that type Design programs so that space is not wasted Type byte short int long float double Storage 8 bits 16 bits 32 bits 64 bits 32 bits 64 bits Min Value ,768 -2,147,483,648 < -9 x /- 3.4 x with 7 significant digits +/- 1.7 x with 15 significant digits Max Value ,767 2,147,483,647 > 9 x 10 18

Integers and floating point types By default JAVA assumes all integer literals are of type int To define a literal of type long L or l is appended to the end of the value Example: long counted_Stars = L ; JAVA assumes floating point literals are of type double If we need to treat a floating point as a float we append f or F to the end of the value Example: float ratio = F;

characters A char variable stores a single character Character literals are delimited by single quotes Example Data type char represents a single character Example: char topGrade = ‘A’; Characters include Uppercase, lowercase letters; punctuation ; etc.. 'a' 'X' '7' '$' ',' '\n'

Boolean type Declaration Example: boolean flag = true; Boolean variables have only two valid values true and false This type is used to represent situation with 2 states Example: a light bulb being on (true) or off (false)

Integers and floating point types By default JAVA assumes all integer literals are of type int To define a literal of type long L or l is appended to the end of the value Example: long counted_Stars = L ; JAVA assumes floating point literals are of type double If we need to treat a floating point as a float we append f or F to the end of the value Example: float ratio = F;

Outline Character Strings Variables and Assignment Primitive Data Types Expressions Data Conversion Interactive Programs Graphics Applets Drawing Shapes