Chapter 3 (in our edition)

Fundamental Data Types

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

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

Primitive Types

Type	Description	Size
int	The integer type, with range -2,147,483,648 . . . 2,147,483,647	4 bytes
byte	The type describing a single byte, with range -128 . . . 127	1 byte
short	The short integer type, with range -32768 . . . 32767	2 bytes
long	The long integer type, with range -9,223,372,036,854,775,808 . . . -9,223,372,036,854,775,807	8 bytes
double	The double-precision floating-point type, with a range of about ±10³⁰⁸ and about 15 significant decimal digits	8 bytes
float	The single-precision floating-point type, with a range of about ±10³⁸ and about 7 significant decimal digits	4 bytes
char	The character type, representing code units in the Unicode encoding scheme	2 bytes
boolean	The type with the two truth values false and true	1 bit

Number Types: Floating-point Types

Rounding errors occur when an exact conversion between numbers is not possible
double f = 4.35; System.out.println(100 * f); // prints 434.99999999999994
Java: Illegal to assign a floating-point expression to an integer variable
double balance = 13.75; int dollars = balance; // Error
Casts: used to convert a value to a different type
int dollars = (int) balance; // OK
Cast discards fractional part.
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

Syntax 4.1: Cast

(typeName) expression

Example:

(int) (balance * 100)

Purpose:

To convert an expression to a different type

Self Check

Which are the most commonly used number types in Java?
When does the cast (long) x yield a different result from the call Math.round(x)?
How do you round the double value x to the nearest int value, assuming that you know that it is less than 2 · 10⁹?

Answers

int and double
When the fractional part of x is ≥ 0.5
By using a cast: (int) Math.round(x)

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;

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;

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

File CashRegister.java

File CashRegisterTester.java

Output

   Change=0.25
   Change=2.0

Self Check

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;
What is wrong with the following statement?
double circumference = 3.14 * diameter;

Answers

The first definition is used inside a method, the second inside a class
(1) You should use a named constant, not the "magic number" 3.14
(2) 3.14 is not an accurate representation of π

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

Assignment, Increment, and Decrement

Self Check

What is the meaning of the following statement?
balance = balance + amount;
What is the value of n after the following sequence of statements?
```
n--;
n++;
n--;
```

Answers

The statement adds the amount value to the balance variable
One less than it was before

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

Arithmetic Operations

final int PENNIES_PER_NICKEL = 5;
final int PENNIES_PER_DIME = 10;
final int PENNIES_PER_QUARTER = 25;
final int 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;

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)

Mathematical Methods in Java

`Math.sqrt(x)`	square root
`Math.pow(x, y)`	power x^y
`Math.exp(x)`	e^x
`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
Math.min(x, y), Math.max(x, y)	minimum, maximum

Analyzing an Expression

Self Check

What is the value of 1729 / 100? Of 1729 % 100?
Why doesn't the following statement compute the average of s1, s2, and s3?
double average = s1 + s2 + s3 / 3; // Error
What is the value of Math.sqrt(Math.pow(x, 2) + Math.pow(y, 2)) in mathematical notation?

Answers

17 and 29
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

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
```

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

Self Check

Why can't you call x.pow(y) to compute x^y?
Is the call System.out.println(4) a static method call?

Answers

x is a number, not an object, and you cannot invoke methods on numbers
No–the println method is called on the object System.out

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: ""

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
```

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);

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 = "Hello, World!";
String sub = greeting.substring(0, 5); // sub is "Hello"

Supply start and “past the end” position
First position is at 0
Substring length is “past the end” - start

Self Check

Assuming the String variable s holds the value "Agent", what is the effect of the assignment s = s + s.length()?
Assuming the String variable river holds the value "Mississippi", what is the value of river.substring(1, 2)? Of river.substring(2, river.length() - 3)?

Answers

s is set to the string Agent5
The strings "i" and "ssissi"

International Alphabets

International Alphabets

International Alphabets

Reading Input

System.in has minimal set of features–it can only read one byte at a time
In Java 5.0, Scanner class was added to read keyboard input in a convenient manner

Scanner in = new Scanner(System.in);
System.out.print("Enter quantity: ");
int quantity = in.nextInt();

nextDouble reads a double
nextLine reads a line (until user hits Enter)
nextWord reads a word (until any white space)

File InputTester.java

Output

   Enter price: 7.55
   Enter dollars: 10
   Enter quarters: 2
   Enter dimes: 1
   Enter nickels: 0
   Enter pennies: 0
   Your change is 3.05

Reading Input From a Dialog Box

Reading Input From a Dialog Box

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

Self Check

Why can't input be read directly from System.in?
Suppose in is a Scanner object that reads from System.in, and your program calls
String name = in.next();
What is the value of name if the user enters John Q. Public?

Answers

The class only has a method to read a single byte. It would be very tedious to form characters, strings, and numbers from those bytes.
The value is "John". The next method reads the next word.

Chapter 3 (in our edition)

Fundamental Data Types

Chapter Goals

Number Types

Primitive Types

Number Types: Floating-point Types

Syntax 4.1: Cast

Example:

Purpose:

Self Check

Answers

Constants: final

Constants: static final

Syntax 4.2: Constant Definition

Example:

Purpose:

File CashRegister.java

File CashRegisterTester.java

Output

Self Check

Answers

Assignment, Increment, and Decrement

Assignment, Increment, and Decrement

Self Check

Answers

Arithmetic Operations

Arithmetic Operations

The Math class

Mathematical Methods in Java

Analyzing an Expression

Self Check

Answers

Calling Static Methods

Syntax 4.3: Static Method Call

Example:

Purpose:

Self Check

Answers

Strings

Concatenation

Concatenation in Print Statements

Converting between Strings and Numbers

Substrings

Self Check

Answers

International Alphabets

International Alphabets

International Alphabets

Reading Input

File InputTester.java

Output

Reading Input From a Dialog Box

Reading Input From a Dialog Box

Self Check

Answers

Constants: `final`

Constants: `static final`

The `Math` class