Outline Character Strings Variables and Assignment Primitive Data

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

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

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

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

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

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 l A constant l is an identifier that is similar to a variable l except that it holds the same value l During its entire existence l By giving the value a name => explain role in program l is named using uppercase letters l l 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) l The compiler l Produces an error message l if you attempt to change the value of a constant l This prevents coding errors l Because the only valid place to change their value l is the initial assignment

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

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

JAVA Primitive data types l All the numeric types differ l By the amount of memory space used l l To store a value of that type Design programs so that space is not wasted Type Storage Min Value Max Value byte short int long 8 bits 16 bits 32 bits 64 bits -128 -32, 768 -2, 147, 483, 648 < -9 x 1018 127 32, 767 2, 147, 483, 647 > 9 x 1018 float double 32 bits 64 bits +/- 3. 4 x 1038 with 7 significant digits +/- 1. 7 x 10308 with 15 significant digits

Integers and floating point types l By default l JAVA assumes all integer literals are of type int l To define a literal of type long l l L or l is appended to the end of the value Example: long counted_Stars = 86827263927 L; l JAVA assumes floating point literals are of type double l If we need to treat a floating point as a float l l we append f or F to the end of the value Example: float ratio = 0. 2363 F;

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

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

Integers and floating point types l By default l JAVA assumes all integer literals are of type int l To define a literal of type long l l L or l is appended to the end of the value Example: long counted_Stars = 86827263927 L; l JAVA assumes floating point literals are of type double l If we need to treat a floating point as a float l l we append f or F to the end of the value Example: float ratio = 0. 2363 F;

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