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Chapter 3

Fundamental Data TypesNumber Types (3.1)

Assignment (3.2)Constants (3.3)

Arithmetic and Mathematical Functions (3.4)Calling Static methods (3.5)

Quality Tips 3.1, 3.2Advanced Topics 3.1, 3.3Common Error 3.1, 3.2

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Java primitive types - examples

int 3 4 -700 32767 -21211 0

double3.456 -3456.789 0.6 0.0

char'd' 'a' '*'

booleantrue false

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Numbers

Integers•int type denotes integers.

• Integers can have a range of -2,147,483,648 to 2,147,483,647. • Remember, an int is represented using 32 bits.

• If you need to handle integral values beyond that range, use long (64 bits).

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Numbers

Floating-point numbers•double type denotes floating point numbers.

• go to about 10300. • Remember, an double is represented using 64

bits.

•double numbers suffer from precision problems. They store only about 15 significant digits.

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Precision Problem:

double originalPrice = 3E14;(3*1014)300,000,000,000,000.00

double discountedPrice = originalPrice – 0.05;299,999,999,999,999.95

double discount = originalPrice - discountedPrice;

System.out.println(discount); //Should print 0.05, prints 0.0625

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Arithmetic Operations

addition + subtraction - multiplication * division / remainder % (integer operation)

• 7 % 3 = 1

• 1 % 3 = 1

• 8 % 4 = 0

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Rules of Arithmetic:

2 + 3 = 5 2 + 3.0 = 5.0 2.0 + 3 = 5.0 2.0 + 3.0 = 5.0 7.0 / 2.0 = 3.5 7 / 2 = 3 3 / 4 = 0 3.0 / 4 = 0.75

5 % 2 + 6 = 1 + 2 * 3 / 5 = 6 / 7 * 4 = 6.0 / 2.0 * 5 = 1 - 8 / 3 = 4 + 4 / 4 % 4 * 4 =

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Rules of Arithmetic:

2 + 3 = 5 2 + 3.0 = 5.0 2.0 + 3 = 5.0 2.0 + 3.0 = 5.0 7.0 / 2.0 = 3.5 7 / 2 = 3 3 / 4 = 0 3.0 / 4 = 0.75

5 % 2 + 6 = 7 1 + 2 * 3 / 5 = 6 / 7 * 4 = 6.0 / 2.0 * 5 = 1 - 8 / 3 = 4 + 4 / 4 % 4 * 4 =

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Rules of Arithmetic:

2 + 3 = 5 2 + 3.0 = 5.0 2.0 + 3 = 5.0 2.0 + 3.0 = 5.0 7.0 / 2.0 = 3.5 7 / 2 = 3 3 / 4 = 0 3.0 / 4 = 0.75

5 % 2 + 6 = 7 1 + 2 * 3 / 5 = 2 6 / 7 * 4 = 6.0 / 2.0 * 5 = 1 - 8 / 3 = 4 + 4 / 4 % 4 * 4 =

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Rules of Arithmetic:

2 + 3 = 5 2 + 3.0 = 5.0 2.0 + 3 = 5.0 2.0 + 3.0 = 5.0 7.0 / 2.0 = 3.5 7 / 2 = 3 3 / 4 = 0 3.0 / 4 = 0.75

5 % 2 + 6 = 7 1 + 2 * 3 / 5 = 2 6 / 7 * 4 = 0 6.0 / 2.0 * 5 = 1 - 8 / 3 = 4 + 4 / 4 % 4 * 4 =

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Rules of Arithmetic:

2 + 3 = 5 2 + 3.0 = 5.0 2.0 + 3 = 5.0 2.0 + 3.0 = 5.0 7.0 / 2.0 = 3.5 7 / 2 = 3 3 / 4 = 0 3.0 / 4 = 0.75

5 % 2 + 6 = 7 1 + 2 * 3 / 5 = 2 6 / 7 * 4 = 0 6.0 / 2.0 * 5 = 15.0 1 - 8 / 3 = 4 + 4 / 4 % 4 * 4 =

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Rules of Arithmetic:

2 + 3 = 5 2 + 3.0 = 5.0 2.0 + 3 = 5.0 2.0 + 3.0 = 5.0 7.0 / 2.0 = 3.5 7 / 2 = 3 3 / 4 = 0 3.0 / 4 = 0.75

5 % 2 + 6 = 7 1 + 2 * 3 / 5 = 2 6 / 7 * 4 = 0 6.0 / 2.0 * 5 = 15.0 1 - 8 / 3 = -1 4 + 4 / 4 % 4 * 4 =

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Rules of Arithmetic:

2 + 3 = 5 2 + 3.0 = 5.0 2.0 + 3 = 5.0 2.0 + 3.0 = 5.0 7.0 / 2.0 = 3.5 7 / 2 = 3 3 / 4 = 0 3.0 / 4 = 0.75

5 % 2 + 6 = 7 1 + 2 * 3 / 5 = 2 6 / 7 * 4 = 0 6.0 / 2.0 * 5 = 15.0 1 - 8 / 3 = -1 4 + 4 / 4 % 4 * 4 = 8

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Assignment

public Circle()

{diameter = 30;

xPosition = 20;

yPosition = 6;

color = "magenta";

isVisible = false;

} The = operator is called the assignment operator.

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Assignment

On the left side of the assignment operator you must have a variable name.

On the right side of the assignment operator you may have a single value or an expression.•diameter = 30;

•balance = balance + howMuch;

•circumference = 3.14 * diameter;

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Assignment

• Arithmetic operations can be combined with the assignment operator.•balance += howMuch;•balance -= howMuch;

• Operations combined with assignment+=

-=

*=

/=

%=

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Increment/Decrement Operators

int count = 0;

count++; //count is now 1;

count += 3; //count is now 4;

count--; //count is now 3;

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Operator Order of Precedence

++ -- * / % + - = *= /= %= += -=

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Constants

A final variable is a constant. Once its value is set, it cannot be changed.

final variables are named with all capital letters.

Do not use magic numbers in your programs. If you have a need to do this, rethink….should this be a final variable?

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Circle class

Let's add•findCircumference()•findArea()

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Examplepublic class Circle{ // Constructor goes here

// Returns the circumference of the Circlepublic double findCircumference(){ //code goes here

}

// Returns the area of the Circlepublic double findArea(){ //code goes here

}

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Examplepublic class Circle{ // Other code goes here

// Returns the circumference of the Circlepublic double findCircumference(){ return 3.14 * diameter; //magic number

}

// Returns the area of the Circlepublic double findArea(){

double radius = diamter/2; return 3.14 * radius * radius; //magic number

}

}

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Examplepublic class Circle{

// Other code goes here

// Returns the circumference of the Circlepublic double findCircumference(){ return PI * diameter; //magic number replaced

}

// Returns the area of the Circlepublic double findArea(){ double radius = diamter/2; return PI * radius * radius; //magic number replaced

} private static final double PI = 3.1415926;

//private instance fields declared here}

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Other useful constants

TAX_RATE DIME_VALUE QUARTER_VALUE PENNIES_PER_DOLLAR HOURS_IN_DAY MINUTES_IN_HOUR MAX_SEATS

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the Math class

Java provides certain math finctions for us. The Math class contains methods that can be very useful (page 95 of your text).

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Useful methods in Math classMethod Returns

Math.sqrt(x) square root of x (>=0)

Math.pow(x,y) xy

Math.abs(x) absolute value of x

Math.max(x,y) The larger of x and y

Math.min(x,y) The smaller of x and y

Math.ceil(x) Smallest integer >= x

Math.floor(x) Largest integerr <= x

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All methods in the Math class

Our first look at the API !

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Static methods

The Math class contains static methods. This means that the method does not

operate on a particular object. You do not instantiate an object of the Math class in order to use the methods of the Math class.

You invoke the square root method by•Math.sqrt(4)

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The quadratic formula

2 4

2

b b acx

a

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The quadratic formula

2 4

2

b b acx

a

Write assignment statements that will return the two roots, x1 and x2.

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Answers

x1 = (-b + Math.sqrt(b*b – 4*a*c))/(2*a);

x2 = (-b - Math.sqrt(b*b – 4*a*c))/(2*a);

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A better way…

double root = Math.sqrt(b * b – 4 * a * c);

x1 = (-b + root) / (2*a);

x2 = (-b - root) / (2*a);

Why is this way "better"?

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The Math class

Java API – look at field summary. How does this change our findCircumference and findArea methods in out Circle class?

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Examplepublic class Circle{

// Other code goes here

// Returns the circumference of the Circlepublic double findCircumference(){ return PI * diameter; //magic number replaced

}

// Returns the area of the Circlepublic double findArea(){ double radius = diamter/2; return PI * radius * radius; //magic number replaced

} private static final double PI = 3.1415926;

//private instance fields declared here}

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Examplepublic class Circle{

// Other code goes here

// Returns the circumference of the Circlepublic double findCircumference(){ return Math.PI * diameter; //final variable replaced

}

// Returns the area of the Circlepublic double findArea(){ double radius = diamter/2; return Math.PI * radius * radius; //final variable replaced

}

//private instance fields declared here}

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Our BankAccount Class

Let's add a method computeInterest().•computeInterest will increase our current

balance by 2.5%.

Let's add a method chargeServiceFee().•chargeServiceFee()will deduct $9.95 from our

balance.

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Reminders about naming conventions A variable name must be a legal identifier and not a

keyword (double, int, new, etc.) or null.

By Convention :  Variable names begin with a lowercase letter, and class names begin with an uppercase letter. If a variable name consists of more than one word, the words are joined together, and each word after the first begins with an uppercase letter, like this: isVisible. The underscore character (_) is used to separate words in constants(final variables are named with all caps).

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Reminders about object variables and object references

Circle sun;• defines an object variable or type Circle.

new Circle(); • constructs a Circle object.

Circle otherSun = new Circle();• constructs a Circle object and assigns it to the

object variable otherSun.

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Reminders aboutmethods and parameters

Circle sun(30,10,40,"yellow");• 30, 10, 40, "yellow" are construction parameters (provide information for

the construction of the object). b1.deposit(100);

• 100 is a value passed to the method deposit. deposit (double howMuch);

• howMuch is a parameter of the method deposit. In a method definition, each parameter has a type and a name. The

parameters are separated by commas. In a method call, the values passed must be consistent with the

parameters listed in the method header. A method definition specifies the access modifier, the return type,

the method name, the parameters, and the statements for performing the task.

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Reminders about errors A compile-time error

• a syntax error is a violation of the rules of the language• missing semicolon• misspelled identifier• missing { or }

A runtime error • division by 0;• NullPointerException (didn't initialize an object field)

A logic error (an error of intent?)• program executes but performs a task that was not

intended by the programmer.

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Reminders about types

Primitive types• int

• double

• char

• boolean

Everything else is a reference

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Number variables versesObject variables

Number variables hold values:

diameter = 30;

anotherNumber = diameter

diameter = 40;

Changing diameter DOES NOT affect the value of anotherNumber.

30 30

diameter anotherNumber

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Number variables versesObject variables

Object variables hold references:

BankAccount b1 = new BalkAccount(1000);

BankAccount b2 = b1

b1.deposit(200);

Changing b1 DOES affect the b2.

balance = 1000b1

b2