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Chapter 3

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 

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Chapter 3

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  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  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. 29public 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  * QUARTER_VALUE; 51   } 52 …Continue

  16. 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. Math Function Arguments • Use online help to confirm input and output data types for math functions, most require floating point data • http://java.sun.com/j2se/1.4/docs/api/index.html

  22. Analyzing an Expression

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

  24. 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);

  25. Syntax 3.3 : Cast (typeName)expression Example: (int)(x + 0.5) Purpose: To convert an expression to a different type

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