Fundamentals of Data Types - Numbers, Strings, and Constants

1. Chapter 3 Fundamental Data Types

2. 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

3. 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) . . .. . . }

4. Number types • int: integers, no fractional part1, -4, 0 • double: floating-point numbers (double precision)0.5, -3.11111, 4.3E24, 1E-14

5. Implementing the getTotal Method • public class Purse{ public double getTotal(){ return nickels * 0.05 + dimes * 0.1 + quarters * 0.25; } private int nickels; private int dimes; private int quarters;}* = multiplication

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

7. Assignment

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

9. 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; }

10. 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 isPurse.DIME_VALUE

11. 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

12. 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

13. 16   /** 17      Add nickels to the purse. 18      @param 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. 27      @param count the number of dimes to add 28   */ Continue…

14. 29   public void addDimes(int count) 30   { 31      dimes = dimes + count; 32   } 3334   /** 35      Add quarters to the purse. 36      @param count the number of quarters to add 37   */ 38   public void addQuarters(int count) 39   { 40      quarters = quarters + count; 41   } 42 …Continue

15. 43   /** 44      Get the total value of the coins in the purse. 45      @return 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

16. 53   private static final double NICKEL_VALUE = 0.05;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; 56 57   private int nickels; 58   private int dimes; 59   private int quarters; 60} 61

17. 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

18. 12      myPurse.addQuarters(2); 13 14      double totalValue = myPurse.getTotal(); 15      System.out.print("The total is "); 16      System.out.println(totalValue); 17   } 18}

19. Division and Remainder • / is the division operator • If both arguments are integers, the result is an integer. The remainder is discarded • 7.0 / 4 = 1.757 / 4 = 1 • Get the remainder with % (pronounced "modulo")7 % 4 = 3

20. Mathematical Functions

21. Analyzing an Expression

22. 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.

23. 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);

24. 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

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

26. 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"      

27. 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);

28. Substrings • String greeting = "Clown";String sub = greeting.substring(1, 4); • Supply start and “past the end” position • First position is at 00C1l2o3w4 n • substring length = “past the end” - start

29. 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 • AddSystem.exit(0)to the main method of any program that uses JOptionPane

30. An Input Dialog

31. 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

32. 11 12      String input = JOptionPane.showInputDialog("How many nickels do you have?"); 13      int count = Integer.parseInt(input); 14      myPurse.addNickels(count); 15 16      input = JOptionPane.showInputDialog("How many dimes do you have?"); 17      count = Integer.parseInt(input); 18      myPurse.addDimes(count); 19 20      input = JOptionPane.showInputDialog("How many quarters do you have?"); …Continue

33. 21      count = Integer.parseInt(input); 22      myPurse.addQuarters(count); 23 24      double totalValue = myPurse.getTotal(); 25      System.out.println("The total is " + totalValue); 26 27      System.exit(0); 28   } 29}

34. 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'

35. Copying Numbers • double balance1 = 1000;double balance2 = balance1;balance2 = balance2 + 500; • Change in balance2 does not affect balance1

36. 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

37. Copying Object References