Chapter 3 Fundamental Data Types

Chapter Goals To understand integer and floating-point numbers To recognize the limitations of the int and double types and the overflow and round off errors that can result To write arithmetic expressions in Java To use the String type to define and manipulate character strings To learn about the char data type To learn how to read program input To understand the copy behavior of primitive types and object references

Purse Class Interface public class Purse { public void addNickels(int count)... public void addDimes(int count)... public void addQuarters(int count)... public double getTotal(int count) }

Number types int: integers, no fractional part 1, -4, 0 double: floating-point numbers (double precision) 0.5, , 4.3E24, 1E-14

Implementing the getTotal Method public class Purse { public double getTotal(){ return nickels * dimes * quarters * 0.25; } private int nickels; private int dimes; private int quarters; } * = multiplication

Assignment operator public Purse() { nickels = 0; dimes = 0; quarters = 0; } public void addNickels(int count) { nickels = nickels + count; }

Assignment

Increment/Decrement nickels++ is the same as nickels = nickels + 1 nickels-- decrements the contents of the variable.

Constants public double getTotal() { final double NICKEL_VALUE = 0.05; final double DIME_VALUE = 0.1; final double QUARTER_VALUE = 0.25; return nickels * NICKEL_VALUE + dimes * DIME_VALUE + quarters * QUARTER_VALUE; }

Class Constants public class Purse{... public double getTotal(){ return nickels * NICKEL_VALUE + dimes * DIME_VALUE + quarters * QUARTER_VALUE; } private static final double NICKEL_VALUE = 0.05; private static final double DIME_VALUE = 0.1; private static final double QUARTER_VALUE = 0.25;... } In methods of other classes, the constant is Purse.DIME_VALUE

Syntax 3.1: Constant Definition Example: Purpose: In a method: final typeName variableName= expression ; In a class: accessSpecifier static final typeName variableName = expression; Example: final double NICKEL_VALUE =0.05; public static final double LITERS_PER_GALLON =3.785; Purpose: To define a constant of a particular type

File Purse.java 1/** 2 A purse computes the total value of a collection of coins. 3*/ 4public class Purse 5{ 6 /** 7 Constructs an empty purse. 8 */ 9 public Purse() 10 { 11 nickels = 0; 12 dimes = 0; 13 quarters = 0; 14 } 15…Continue

16 /** 17 Add nickels to the purse. count the number of nickels to add 19 */ 20 public void addNickels(int count) 21 { 22 nickels = nickels + count; 23 } 2425 /** 26 Add dimes to the purse. count the number of dimes to add 28 */ Continue…

29 public void addDimes(int count) 30 { 31 dimes = dimes + count; 32 } 3334 /** 35 Add quarters to the purse. count the number of quarters to add 37 */ 38 public void addQuarters(int count) 39 { 40 quarters = quarters + count; 41 } 42 …Continue

43 /** 44 Get the total value of the coins in the purse. the sum of all coin values 46 */ 47 public double getTotal() 48 { 49 return nickels * NICKEL_VALUE 50 + dimes * DIME_VALUE + quarters * QUARTE R_VALUE; 51 } 52 …Continue

53 private static final double NICKEL_VALUE = 0.05; 54 private static final double DIME_VALUE = 0.1; 55 private static final double QUARTER_VALUE = 0.25; private int nickels; 58 private int dimes; 59 private int quarters; 60} 61

File PurseTest.java 1/** 2 This program tests the Purse class. 3*/ 4public class PurseTest 5{ 6 public static void main(String[] args) 7 { 8 Purse myPurse = new Purse(); 9 10 myPurse.addNickels(3); 11 myPurse.addDimes(1); …Continue

12 myPurse.addQuarters(2); double totalValue = myPurse.getTotal(); 15 System.out.print("The total is "); 16 System.out.println(totalValue); 17 } 18}

Division and Remainder / is the division operator If both arguments are integers, the result is an integer. The remainder is discarded 7.0 / 4 = / 4 = 1 Get the remainder with % (pronounced "modulo") 7 % 4 = 3

Mathematical Functions Math.sqrt(x)square root Math.pow(x, y)power x y Math.exp(x)exex Math.log(x)natural log Math.sin(x), Math.cos(x), Math.tan(x) sine, cosine, tangent (x in radian) Math.round(x)closest integer to x

Analyzing an Expression

Syntax 3.2: Static Method Call ClassName. methodName ( Tparameters) Example: Math.sqrt(4) Purpose: To invoke a static method (a method that doesn't operate on an object) and supply its parameters.

Type Conversion In assignment, types must match. double total = "a lot"; // no Use “cast” (int) to convert floating-point values to integer values: int pennies = (int)(total * 100); Cast discards fractional part. Use Math.round for rounding: int dollar = (int)Math.round(total);

Syntax 3.3 : Cast (typeName)expression Example: (int)(x + 0.5) (int)Math.round(100 * f) Purpose: To convert an expression to a different type

Strings String constants: "Carl" String variables: String name = "Carl"; String length: int n = name.length();

Concatenation String fname = "Harry"; String lname = "Hacker"; String name = fname + lname; name is "HarryHacker" If one operand of + is a string, the other is converted to a string: String a = "Agent"; String name = a + 7; name is "Agent7"

Converting between Strings and Numbers Convert to number: int n = Integer.parseInt(str); double x = Double.parseDouble(x); Convert to string: String str = "" + n; str = Integer.toString(n);

Substrings String greeting = "Clown"; String sub = greeting.substring(1, 4); Supply start and “past the end” position First position is at 0 0 C 1 l 2 o 3 w 4 n substring length = “past the end” - start

Reading Input String input = JOptionPane.showInputDialog(prompt) Convert strings to numbers if necessary: int count = Integer.parseInt(input); Conversion throws an exception if user doesn't supply a number--see chapter 15 Add System.exit(0) to the main method of any program that uses JOptionPane

An Input Dialog

File InputTest.java 1import javax.swing.JOptionPane; 2 3/** 4 This program tests input from an input dialog. 5*/ 6public class InputTest 7{ 8 public static void main(String[] args) 9 { 10 Purse myPurse = new Purse(); …Continue

11 12 String input = JOptionPane.showInputDialog( "How many nickels do you have?"); 13 int count = Integer.parseInt(input); 14 myPurse.addNickels(count); input = JOptionPane.showInputDialog("How many dimes do you have?"); 17 count = Integer.parseInt(input); 18 myPurse.addDimes(count); input = JOptionPane.showInputDialog("How many quarters do you have?"); …Continue

21 count = Integer.parseInt(input); 22 myPurse.addQuarters(count); double totalValue = myPurse.getTotal(); 25 System.out.println("The total is " + totalValue); System.exit(0); 28 } 29}

Characters char: character type—a single Unicode character Character constants use single quotes: 'A', '\n', '\u00E9' 'A'is not the same as "A" charAt method gets character from a string "Hello".charAt(0) is 'H'

Copying Numbers double balance1 = 1000; double balance2 = balance1; balance2 = balance ; Change in balance2 does not affect balance1

Copying Object References BankAccount account1 = new BankAccount(1000); BankAccount account2 = account1; account2.deposit(500); Change through account2 is also visible through account1 Object variables hold references, not objects

Copying Object References