Ch4 Data TypesEvery 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:

int idnum; // 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!.

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

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>

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

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;

BankAcct jon = 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