Variable Declaration

1. 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;

2. 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;

3. Add Subtract Multiply Divide Modulus (remainder) + - * / % Arithmetic Operators

4. 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.

5. 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: <variable> = <expression>;

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

7. 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 Compound Assignment Equalities

8. 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 --

9. 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: • double • float • long • int • short • byte

10. 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 47.25 int dollars = (int) weeklyBudget; //dollars will be 47

11. 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.

12. 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”;

13. 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

14. Methods in class KeyboardReader

15. 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)

16. 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); } }

17. Math Class • The math class is quite extensive but we will concentrate a just a few of it’s properties:

18. 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

19. 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 #)

20. 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();

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