4015: ICOM Advanced Programming
Lecture 4
Chapter Four: Fundamental Data Types
ICOM 4015 Fall 2008
Big Java by Cay Horstmann Copyright 2008 by John Wiley & Sons. All rights reserved.
Chapter Four: Fundamental Data Types
ICOM 4015 Fall 2008
BigBig Javayby Cay Horstmann Java b Cay Horstmann Copyright 2008 by John Wiley & Sons. All rights reserved. Copyright 2008 by John Wiley & Sons. All rights reserved.
Chapter Goals To understand integer and floating-point numbers To recognize the limitations of the numeric types To become aware of causes for overflow and roundoff errors To understand the proper use of constants To write arithmetic expressions in Java To use the String type to define and manipulate character strings To learn how to read program input and produce formatted output
ICOM 4015 Fall 2008
BigBig Javayby Cay Horstmann Java b Cay Horstmann Copyright 2008 by John Wiley & Sons. All rights reserved. Copyright 2008 by John Wiley & Sons. All rights reserved.
Number Types int: integers, no fractional part
1, -4, 0
double: floating-point numbers (double precision)
0.5, -3.11111, 4.3E24, 1E-14
A numeric computation overflows if the result falls outside the range for the number type
int n = 1000000; System.out.println(n * n); // prints -727379968
Java: 8 primitive types, including four integer types and two floating point types
ICOM 4015 Fall 2008
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Primitive Types
Type
int
Description The integer type, with range -2,147,483,648 . . . 2,147,483,647 The type describing a single byte, with range -128 . . . 127 The short integer type, with range -32768 . . . 32767 The long integer type, with range -9,223,372,036,854,775,808 . . . -9,223,372,036,854,775,807
Size 4 bytes 1 byte 2 bytes 8 bytes
byte short
long
double
The double-precision floating-point type, with a range of about 10308 and 8 about 15 significant decimal digits bytes The single-precision floating-point type, with a range of about 1038 and about 7 significant decimal digits The character type, representing code units in the Unicode encoding scheme The type with the two truth values false and true
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float
4 bytes 2 bytes 1 bit
char
boolean
BigBig Javayby Cay Horstmann Java b Cay Horstmann Copyright 2008 by John Wiley & Sons. All rights reserved. Copyright 2008 by John Wiley & Sons. All rights reserved.
Number Types: Floating-point Types Rounding errors occur when an exact conversion between numbers is not possible Java: Illegal to assign a floating-point expression to an integer variable
double balance = 13.75; int dollars = balance; // Error double f = 4.35; System.out.println(100 * f); // prints 434.99999999999994
Casts: used to convert a value to a different type
int dollars = (int) balance; // OK
Cast discards fractional part.
Continued
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Number Types: Floating-point Types (cont.)
Math.round
converts a floating-point number to nearest integer
long rounded = Math.round(balance); // if balance is 13.75, then // rounded is set to 14
ICOM 4015 Fall 2008
BigBig Javayby Cay Horstmann Java b Cay Horstmann Copyright 2008 by John Wiley & Sons. All rights reserved. Copyright 2008 by John Wiley & Sons. All rights reserved.
Syntax 4.1 Cast
(typeName) expression
Example:
(int) (balance * 100)
Purpose: To convert an expression to a different type.
ICOM 4015 Fall 2008
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Self Check 4.1 Which are the most commonly used number types in Java? Answer: int and double
ICOM 4015 Fall 2008
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Self Check 4.2 When does the cast (long) x yield a different result from the call Math.round(x)? Answer: When the fractional part of x is 0.5
ICOM 4015 Fall 2008
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Self Check 4.3 How do you round the double value x to the nearest int value, assuming that you know that it is less than 2 109? Answer: By using a cast: (int) Math.round(x)
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Constants: final A final variable is a constant Once its value has been set, it cannot be changed Named constants make programs easier to read and maintain Convention: use all-uppercase names for constants
final double QUARTER_VALUE = 0.25; final double DIME_VALUE = 0.1; final double NICKEL_VALUE = 0.05; final double PENNY_VALUE = 0.01; payment = dollars + quarters * QUARTER_VALUE + dimes * DIME_VALUE + nickels * NICKEL_VALUE + pennies * PENNY_VALUE;
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Constants: static final If constant values are needed in several methods, declare them together with the instance fields of a class and tag them as static and final Give static final constants public access to enable other classes to use them
public class Math { ... public static final double E = 2.7182818284590452354; public static final double PI = 3.14159265358979323846; } double circumference = Math.PI * diameter;
ICOM 4015 Fall 2008
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Syntax 4.2 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 in a method or a class.
ICOM 4015 Fall 2008
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ch04/cashregister/CashRegister.java
01: 02: 03: 04: 05: 06: 07: 08: 09: 10: 11: 12: 13: 14: 15: 16: 17: 18: 19: 20: 21: 22: /** A cash register totals up sales and computes change due. */ public class CashRegister { /** Constructs a cash register with no money in it. */ public CashRegister() { purchase = 0; payment = 0; } /** Records the purchase price of an item. @param amount the price of the purchased item */ public void recordPurchase(double amount) { purchase = purchase + amount; }
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Continued
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ch04/cashregister/CashRegister.java (cont.)
23: 24: 25: 26: 27: 28: 29: 30: 31: 32: 33: 34: 35: 36: 37: 38: 39: 40: 41: 42: 43: 44: /** Enters the payment received from the customer. @param dollars the number of dollars in the payment @param quarters the number of quarters in the payment @param dimes the number of dimes in the payment @param nickels the number of nickels in the payment @param pennies the number of pennies in the payment */ public void enterPayment(int dollars, int quarters, int dimes, int nickels, int pennies) { payment = dollars + quarters * QUARTER_VALUE + dimes * DIME_VALUE + nickels * NICKEL_VALUE + pennies * PENNY_VALUE; } /** Computes the change due and resets the machine for the next customer. @return the change due to the customer */ public double giveChange() {
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Continued
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ch04/cashregister/CashRegister.java (cont.)
45: 46: 47: 48: 49: 50: 51: 52: 53: 54: 55: 56: 57: 58: } double change = payment - purchase; purchase = 0; payment = 0; return change; } public public public public static static static static final final final final double double double double QUARTER_VALUE = 0.25; DIME_VALUE = 0.1; NICKEL_VALUE = 0.05; PENNY_VALUE = 0.01;
private double purchase; private double payment;
ICOM 4015 Fall 2008
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ch04/cashregister/CashRegisterTester.java
01: 02: 03: 04: 05: 06: 07: 08: 09: 10: 11: 12: 13: 14: 15: 16: 17: 18: 19: 20: 21: 22: 23: 24: /** This class tests the CashRegister class. */ public class CashRegisterTester { public static void main(String[] args) { CashRegister register = new CashRegister(); register.recordPurchase(0.75); register.recordPurchase(1.50); register.enterPayment(2, 0, 5, 0, 0); System.out.print("Change: "); System.out.println(register.giveChange()); System.out.println("Expected: 0.25"); register.recordPurchase(2.25); register.recordPurchase(19.25); register.enterPayment(23, 2, 0, 0, 0); System.out.print("Change: "); System.out.println(register.giveChange()); System.out.println("Expected: 2.0"); } ICOM 4015 Fall 2008 }
BigBig Javayby Cay Horstmann Java b Cay Horstmann Copyright 2008 by John Wiley & Sons. All rights reserved. Copyright 2008 by John Wiley & Sons. All rights reserved.
ch04/cashregister/CashRegisterTester.java (cont.) Output:
Change: 0.25 Expected: 0.25 Change: 2.0 Expected: 2.0
ICOM 4015 Fall 2008
BigBig Javayby Cay Horstmann Java b Cay Horstmann Copyright 2008 by John Wiley & Sons. All rights reserved. Copyright 2008 by John Wiley & Sons. All rights reserved.
Self Check 4.4 What is the difference between the following two statements?
final double CM_PER_INCH = 2.54;
and
public static final double CM_PER_INCH = 2.54;
Answer: The first definition is used inside a method, the second inside a class.
ICOM 4015 Fall 2008
BigBig Javayby Cay Horstmann Java b Cay Horstmann Copyright 2008 by John Wiley & Sons. All rights reserved. Copyright 2008 by John Wiley & Sons. All rights reserved.
Self Check 4.5 What is wrong with the following statement?
double circumference = 3.14 * diameter;
Answer: (1) You should use a named constant, not the "magic number" 3.14 (2) 3.14 is not an accurate representation of .
ICOM 4015 Fall 2008
BigBig Javayby Cay Horstmann Java b Cay Horstmann Copyright 2008 by John Wiley & Sons. All rights reserved. Copyright 2008 by John Wiley & Sons. All rights reserved.
Assignment, Increment, and Decrement Assignment is not the same as mathematical equality:
items = items + 1; items++ is the same as items = items + 1 items-- subtracts 1 from items
ICOM 4015 Fall 2008
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Assignment, Increment, and Decrement
ICOM 4015 Fall 2008
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Self Check 4.6 What is the meaning of the following statement?
balance = balance + amount;
Answer: The statement adds the amount value to the balance variable.
ICOM 4015 Fall 2008
BigBig Javayby Cay Horstmann Java b Cay Horstmann Copyright 2008 by John Wiley & Sons. All rights reserved. Copyright 2008 by John Wiley & Sons. All rights reserved.
Self Check 4.7 What is the value of n after the following sequence of statements?
n--; n++; n--;
Answer: One less than it was before.
ICOM 4015 Fall 2008
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Arithmetic Operations / is the division operator If both arguments are integers, the result is an integer. The remainder is discarded 7.0 / 4 yields 1.75 7 / 4 yields 1 Get the remainder with % (pronounced "modulo") 7 % 4 is 3
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Arithmetic Operations
final final final final int int int int PENNIES_PER_NICKEL = 5; PENNIES_PER_DIME = 10; PENNIES_PER_QUARTER = 25; PENNIES_PER_DOLLAR = 100;
// Compute total value in pennies int total = dollars * PENNIES_PER_DOLLAR + quarters * PENNIES_PER_QUARTER + nickels * PENNIES_PER_NICKEL + dimes * PENNIES_PER_DIME + pennies; // Use integer division to convert to dollars, cents int dollars = total / PENNIES_PER_DOLLAR; int cents = total % PENNIES_PER_DOLLAR;
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The Math class Math class: contains methods like sqrt and pow To compute xn, you write Math.pow(x, n) However, to compute x2 it is significantly more efficient simply to compute x * x To take the square root of a number, use the Math.sqrt; for example, Math.sqrt(x) In Java, can be represented as
(-b + Math.sqrt(b * b - 4 * a * c)) / (2 * a)
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Mathematical Methods
Function
Math.sqrt(x) Math.pow(x, y) Math.exp(x) Math.log(x) Math.sin(x), Math.cos(x), Math.tan(x) Math.round(x) Math.min(x, y), Math.max(x, y)
Returns square root power xy ex natural log sine, cosine, tangent (x in radians) closest integer to x minimum, maximum
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Analyzing an Expression
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Self Check 4.8 What is the value of 1729 / 100? Of 1729 % 100? Answer: 17 and 29
ICOM 4015 Fall 2008
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Self Check 4.9 Why doesn't the following statement compute the average of s1, s2, and s3?
double average = s1 + s2 + s3 / 3; // Error
Answer: Only s3 is divided by 3. To get the correct result, use parentheses. Moreover, if s1, s2, and s3 are integers, you must divide by 3.0 to avoid integer division:
(s1 + s2 + s3) / 3.0
ICOM 4015 Fall 2008
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Self Check 4.10 What is the value of Math.sqrt(Math.pow(x, 2) + Math.pow(y, 2)) in mathematical notation? Answer:
ICOM 4015 Fall 2008
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Calling Static Methods A static method does not operate on an object double x = 4;
double root = x.sqrt(); // Error
Static methods are defined inside classes Naming convention: Classes start with an uppercase letter; objects start with a lowercase letter
Math System.out
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Syntax 4.3 Static Method Call
ClassName.methodName(parameters)
Example:
Math.sqrt(4)
Purpose: To invoke a static method (a method that does not operate on an object) and supply its parameters.
ICOM 4015 Fall 2008
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Self Check 4.11 Why can't you call x.pow(y) to compute xy? Answer: x is a number, not an object, and you cannot invoke methods on numbers.
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Self Check 4.12 Is the call System.out.println(4) a static method call? Answer: No the println method is called on the object
System.out.
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Strings A string is a sequence of characters Strings are objects of the String class String constants:
"Hello, World!"
String variables:
String message = "Hello, World!";
String length:
int n = message.length();
Empty string: ""
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Concatenation Use the + operator:
String name = "Dave"; String message = "Hello, " + name; // message is "Hello, Dave"
If one of the arguments of the + operator is a string, the other is converted to a string
String a = "Agent"; int n = 7; String bond = a + n; // bond is "Agent7"
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Concatenation in Print Statements Useful to reduce the number of System.out.print instructions
System.out.print("The total is "); System.out.println(total);
versus
System.out.println("The total is " + total);
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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);
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Substrings
String greeting = "Hello, World!"; String sub = greeting.substring(0, 5); // sub is "Hello"
Supply start and past the end position First position is at 0
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Continued
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Substrings (cont.) Substring length is past the end - start
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