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 Interfacepublic 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 part1, -4, 0

• double: floating-point numbers (double precision)0.5, -3.11111, 4.3E24, 1E-14

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

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 Constantspublic 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

Syntax 3.1: Constant DefinitionExample:  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.java1/**2   A purse computes the total value of a collection of coins.3*/4public class Purse5{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.18      @param count the number of nickels to add19   */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 add28   */

Continue…

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 add37   */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.

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

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

File PurseTest.java1/**2   This program tests the Purse class.3*/4public class PurseTest5{6   public static void main(String[] args)7   {8      Purse myPurse = new Purse();910      myPurse.addNickels(3);11      myPurse.addDimes(1); …Continue

12      myPurse.addQuarters(2);

13

14      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 = 1.75

7 / 4 = 1 • Get the remainder with % (pronounced

"modulo")7 % 4 = 3

Mathematical Functions

Math.sqrt(x) square root

Math.pow(x, y) power xy

Math.exp(x) ex

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 CallClassName. methodName( Tparameters)

Example:Math.sqrt(4)

Purpose:To invoke a static method (a method that doesn'toperate 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

0C1l2o3w4 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.java1import javax.swing.JOptionPane;23/**4   This program tests input from an input dialog.5*/6public class InputTest7{8   public static void main(String[] args)9   {10      Purse myPurse = new Purse();

…Continue

1112      String input = JOptionPane.showInputDialog("How ma

ny nickels do you have?");13      int count = Integer.parseInt(input);14      myPurse.addNickels(count);1516      input = JOptionPane.showInputDialog("How many di

mes do you have?");17      count = Integer.parseInt(input);18      myPurse.addDimes(count);1920      input = JOptionPane.showInputDialog("How many qua

rters do you have?"); …Continue

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}

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 = balance2 + 500;

• 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