Ch4 Data Types

1. Every value has a type associated with it. The computer needs to know how much memory to allocate. Every value is either a primitive type or an ADT: • Abstract Data Types(ADT): • The class is the mechanism for creating user-defined types. These types represent some entity by encapsulating the entities data, instance fields, and methods that manipulate that data. • public class BankAccount{ • // declarations for this class • } • Primitive Data Types (p135): • These are the simple primitive data types we will use: intidnum; // integer values double salary; // real numbers char gender; // single characters ‘M’ or ‘F’ boolean done; // true or false value • Be aware that manipulating real numbers (aka doubles) can result in round-off errors! • Consider: double f = 4.35; System.out.print(100*f); //prints 434.99999999999994 • This occurs because computers represent numbers in binary, and there is no exact representation of the fraction 1/10 in the binary system. So there are limitations!. Ch4 Data Types

2. Type Cast – Conversion between types in Java is common. The following is how to type cast in Java, and it usually results in information loss. • (new Type) expression Examples: • (int)3.14159 • (BankAcct)checkingAcctObject • FYI • BigInteger ADT p137. <optional – working with big numbers> • Constants 4.2// Caps by convention -> static or non-static tbd later! • Use named constants to make programs easier to read and maintain. • Constants are declared as final, and its value cannot be changed. public class TaxSchedule{ private static final double TAX_RATE = 0.075; • Mathematical Constants: //declared in the Math class in the standard library public class Math{ public static final double E = 2.7182818284590452354; public static final double PI = 3.14159265358979323846; • Static – Something that is static belongs to the class – Not an object! double circumference = Math.PI * diameter; // in client code

3. Assignments , Increment & Decrement Operators 4.3 • Common Operation - Incrementing & Decrementing by 1 count = count +1; // increment by 1 count + = 1; // Same as above count + + ; // count - - ; decrement by 1 • Common Operation – Accumulating a sum sum + = score; // sum = sum + score; myBalance + = amt; • Arithmetic Operations & Mathematical Functions 4.4 • Basic: +, -, *, /, % // Be careful of integer division • Advanced ++, --, +=, -=, *=, /= • Resulting Type • int <op> int -> int • int<op>double -> double • Exs: • 3*8 = • 15/3 = //Integer division! • 3/15 = • 15%3 = // Modulus ->Remainder! • 3%2 = • (double)3/15 = • (double)(3/15) = • double result = 3/15; //<eoln>

4. Static Methods 4.5 • Math class methods (p150): ans = Math.sqrt(x); • Static methods belong to the class – not an object! • Consider the following: • answer = Math.sqrt(x); // static method • davesAcct.deposit(amt); // non-static method • sqrt( ) is invoked by the Math class –> it belongs to the class • deposit( ) is invoked by an object • Static Methods: • Belong to the class • Are invoked by the class • DO NOT operate on object

5. Lets open Bluej and input the following: public class Ch4IntroEx{ // Leave room for a class constant public static final double TAX_RATE = 0.03; public static void main(){ final double TWO_DIGITS_PI = 3.14; int x = 5; double radius = 3.35; char gender = 'M'; boolean m359IsCool = true; BankAcctjon = new BankAcct(1000); jon.withdraw(jon.getBalance() * TAX_RATE); System.out.println("jons balance: " +jon.getBalance()); System.out.println("Area of circle with radius = " +radius +"\t: " +(Math.PI * Math.pow(radius,2)) +"\n\t\t<or> less accurately \t: " +(TWO_DIGITS_PI * Math.pow(radius,2))); System.out.println("gender = " +gender); System.out.println("m359IsCool = " +m359IsCool); } } Homework p174 P4.3, P4.5