Variable Declaration  It is possible to declare multiple variables of the same data type on the same line.  Ex. double hours, rate, total;  Variables may also be initialized during multiple declarations  Ex. double hours = 35.5, rate = 8.0, total;

Variable and Constants  It is possible to give a variable a starting value when it is declared. Ex. int x=7; float y=2.345; char initial = ‘K’;  Another variation is to create a constant (i.e. a value that cannot change throughout a program) Ex.final int MAXAGE = 65;

Arithmetic Operators AddSubtractMultiplyDivide Modulus (remainder) + - * / %

Order of Operations  All operators within parentheses are performed first  If there are nested parentheses (parentheses within parentheses) the innermost operators are performed  The *,/,% operators are performed next, from left to right  The + and - are performed last from left to right.

Assignment Statement  An assignment statement is used to assign a value on the left hand side of an equation to a variable on the right.  The command used to create an assignment statement is the equals sign(=).  The general form of an assignment statement is: = ; = ;

Compound Assignment Operations Simple Assignment Compound Addition Compound Subtraction Compound Multiplication Compound Division Compound Remainder =+=-=*=/=%= (integers only)

Compound Assignment Equalities x = x + 10 x = x – 10 x = x * 10 x = x / 10 x = x % 10 x += 10 x –= 10 x *= 10 x /= 10 x %= 10

Increment and Decrement Operators  Increment and Decrement operators add one or subtract one to the value of the variable.  Can be applied to integer, floating point, or character variables.  INCREMENT ++  DECREMENT --

Numeric Type Conversion(TypeCasting)  When you perform arithmetic operations with operands of unlike types, the Java language chooses a unifying type for the result.  The Java programming language then converts nonconforming operands to the unifying type. This unifying type is the type of the involved operand that appears first in the following list: 1.double 2.float 3.long 4.int 5.short 6.byte

Typecasting (cont.)  If you do not want this to happen you have to purposely override the unifying type (typecasting) Ex: int balance= 189; double weeklyBudget = (double)balance/4; //weeklyBudget will be int dollars = (int) weeklyBudget; //dollars will be 47

Strings and Object- Oriented Types  Simple data types are used when simple calculations need to be done.  For more advanced applications, there is a need for strings and object-oriented types.  These types can give the application the ability to (for example) “turn the power on”, “signal if a seat belt is not attached”, “regulate the fuel mixture in an engine”  These data type classes are called class wrappers or object wrappers.

String Data Type  String is used to contain more than one character.  The stored characters must be placed in double quotes.  Many times, processing all input as strings improves reliability of a program because the computer can take in a series of characters, test them to see if they are numbers, and then work with them. Ex: String name=“Rusty”;

String Concatenation  String concatenation is used to combine strings and strings or strings and variables together. Ex. String firstName, lastName, lastFirst; int age = 65; firstName = “John”; lastName = “Doe; lastFirst = lastName + “ “ + firstName + “ is age “ + age; System.out.println (lastFirst); System.out.println(firstName + “ is: \n” + age + “ years old”); Output: Doe John is age 65 John is 65 years old

Methods in class KeyboardReader SignatureDescription char readChar()Returns the first character in the input line, even if it is a space. double readDouble()Returns the first double in the input line. Leading and trailing spaces will be ignored. int readInt()Returns the first integer in the input line. Leading and trailing spaces are ignored String readLine()Returns the input line, including leading and trailing spaces void pause()Returns once the user presses Enter.

Errors  There are three types of errors in programming: syntax, run-time, and logical errors.  Syntax errors occur when you violate a syntax rule (i.e using system.Out.println instead of System.out.println).  Run-time errors occur when you ask a computer to do something it cannot do (i.e divide by zero).  Logic errors occur when you fail to express yourself accurately (i.e using greater than instead of less than)

Example Program public class Example2 { public static void main (String[] args) { int oneint=10; int twoint=15; int sum,difference,product, modulus; float quotient; System.out.print("The first int is "); System.out.println(oneint); System.out.println("The second int is " + twoint); sum = oneint + twoint; difference = oneint - twoint; product = oneint * twoint; modulus = oneint % twoint; quotient = oneint / (float)twoint; System.out.println("The sum is " + sum); System.out.println("The difference is " + difference); System.out.println("The product is " + product); System.out.println("The quotient is " + quotient); System.out.println("The modulus is " + modulus); }

Math Class  The math class is quite extensive but we will concentrate a just a few of it’s properties: abs(int x) Returns the absolute value of x pow(double base, double exponent) Returns the base raised to the exponent. round(double x) Returns x rounded to the nearest whole number. max(int a, int b) Returns the greater of a and b min(int a, int b) Returns the lesser of a and b random() Returns a double value with a positive sign, greater than or equal to 0.0 and less than 1.0. sqrt(double x) Returns the square root of x.

Examples of Math Class Methods int m; double x; m = Math.abs(-7) // m equals 7 x = Math.abs(-7.5)// x equals 7.5 x = Math.pow(3.0,2.0)// x equals 3.0^2.0 = 9.0 x = Math.pow(16.0,.25)// x equals 16.0 ^.25 = 2.0 m = Math.max(20,40)// m equals 40 m = Math.min(20,40)// m equals 20 m = (int) Math.round(4.27)// m equals 4

Math.random  In order to generate a random number between a certain range use the following formula.  X = Math.random() * (high # - low #) + low #  If you want the number to be an integer, you must use the round function.  X = Math.round(Math.random() * (high # - low #) + low #)  Or typecast the formula + 1 to an int  X = (int)(Math.random() * (high # - low # + 1) + low #)

Random Class  Must include  import java.util.Random;  Must then create an object from Random class  Ex: Random name = new Random();  Use object to call methods  Ex: name.method();

Random Class Methods  nextInt(integer);  Generates a random whole number between 0-(integer -1)  nextDouble();  Generates a random decimal between 0.0 – – 1.0