Variables and Constants · Using Variables ! An assignment statement is formed with the variable...

JAVA Ch. 4 Variables and Constants

© 2007 Lawrenceville Press Slide 1

Warm up/Introduction int A = 13; int B = 23; int C; C = A+B; System.out.print(“The answer is” +C);

© 2007 Lawrenceville Press

Slide 2

Declaring and using variables


Slide 3

Declaring Variables � Variable – name for a value stored in

memory. � Variables must be “declared” before they

are used.

� Variable declarations take the form: <data type> <variable name/identifier>;

int length;


Slide 4

Using Variables � An assignment statement is formed with

the variable type and name on the left side of an equal sign; and the value it is to receive on the right side of the equal sign.

int A = 40;

� Operator – the equal sign (=) � Literal – the value to the right of the equal

sign.


Slide 5

Chapter 4

Assignment Statement


Slide 6

An assignment statement gives a value to a variable. Assignment can take several forms: x = 5; a literal (5) is assigned to x x = y + 2; the value of an expression (y + 2) is

assigned to x x = z; the value of another variable (z) is

assigned to x

Using Variables int A = 10; int A;

� What is the difference between the two assignments statements above?

�  If a variable does not include a literal, that variable’s value is going to change as we navigate its class.


Slide 7

Chapter 4 Variable Assignment


Slide 8

A variable can store only one value at any time.

int x; x = 5; x = 10;

x

5 10

Types of Variables


Slide 9

Chapter 4

Primitive Data Types


Slide 10

Type Storage Required int 4 bytes double 8 bytes char 2 bytes boolean 1 bit

Notes: int – integer double – decimal number char – character boolean – true or false

Outputting variable values


Slide 11

Outputting Variables �  When outputting variables we must

concatenate the value of the variable to a string. To do this we put a (+) in front of the variable name in our output statement.

int s = 90; System.out.print(“My score is ” +s “out of 100.”); My score is 90 out of 100.


Slide 12

Current Class Format


Slide 13

/*Name *Date *Class *Period *Class name */ public class ClassName {

public static void main(String[] args) { int A = 10; int B = 20; int C; C= A + B; System.out.print("this is my score "+C); }

}


Slide 14

Variable Initialization

Program statements

/*Name *Date *Class *Period *Class name */ public class ClassName {

public static void main(String[] args) { int A = 10; int B = 80; int C; C= A + B; System.out.print("this is my score "+C); }

}


Slide 15

Practice -


Slide 16

Creating a Ch. 4 Project � Create a new project. Call it… � First initial, last name Chapter 4

�  BBarrett Chapter 4


Slide 17

Practice - �  In your chapter 4 project, create a class titled:

RectanglePerimeter � We will do this together

�  In your chapter 4 project, create a class titled: DistancePtOne � Pg. 79 � You are responsible for completing tis on your

own. Mr. Barrett will help you if needed.


Slide 18

Java Packages


Slide 19

Java Packages � Java has tools that are available to the

programmer. They are called packages, and Java comes ready equipped for them to be used.

� These classes contain general utility classes, and special purpose packages.

� The most fundamental packages is the… Java.util.*;

package


Slide 20

Java Packages: Receiving input from your end-user


Slide 21

Java Packages � The first package we will introduce will be

the: import java.util.Scanner;

Package. This is the ‘import statement’ used to make the package accessible to a method/project.


Slide 22

Java Packages �  Instantiation – after importing our ready-

made package, we must initialize the package. This process is called instantiation.

� The following statement is used to initialize

our scanner:

Scanner input = new Scanner(System.in);


Slide 23

/* *Name *Date *Class *Period *Class name */ public class ClassName {

public static void main(String[] args) {

} } © 2007 Lawrenceville Press

Slide 24

Variable Initialization

Program statements

Package Instantiation

Class importation

import java.util.Scanner;

/* *Name *Date *Class *Period *Class name */ public class ClassName {

public static void main(String[] args) {

-

} } © 2007 Lawrenceville Press

Slide 25

int x = 10; int y = 5; int c;

Program statements


Receiving Data From your end user


Slide 26

§  Part of the java.util.Scanner package

§ To receive data from the end user, the following methods are required.

§ Methods include: variableName = input.nextInt(); variableName = input.nextLine(); variableName = input.next(); variableName = input.nextDouble(); variableName = input.nextBoolean(); Input.close();

Receiving Data From your end user


Slide 27

Methods include: •  input.nextInt(); - integer

•  input.next(); - string

•  input.nextDouble(); - decimal

•  input.nextBoolean(); - boolean

•  input.close(); - closes the input stream

Receiving data example: import java.util.Scanner; int x, y, z;

Scanner input = new Scanner(System.in); System.out.print("Enter your first value: "); x = input.nextInt(); System.out.print("Enter your second value: "); y = input.nextInt(); input.close(); z=x+y;

System.out.print("The sum of your numbers is "+z);


Slide 28

Abstract Data Types


Slide 29

Primitive data types � We already discussed primitive data

types, i.e., integers, doubles, characters, and Booleans; but there is another type of data that we must cover…


Slide 30

Abstract Data Types

� Abstract data type – A class. A data type that can store data and methods.

� Method – A named set of statements that

perform a single, well-defined task. � Object – A variable declared with a class.


Slide 31

Creating a new object… � Creating a new object is called instantiation. In

addition to declaring a variable to refer to the object, the object must be created and initialized in a statement that takes the form:

<class> <variable name> = new <class>(<arguments>);


Slide 32

Abstract Data Types � Where have we seen this before?

<class> <variable name> = new <class>(<arguments>);


Our scanner class is the first abstract data type you have been exposed to.


Slide 33

Chapter 4

Abstract Data Types


Slide 34

A variable declared with a class is called an object. For example, the object spot is type Circle:

Circle spot = new Circle(4);

spot getRadius() area()

Practice


Slide 35

Practice


Slide 36

�  In your chapter 4 project, create a class titled: DistancePtTwo � Page 82 (bottom) � You are responsible for completing this on your

own. Mr. Barrett will help you if needed.

Algorithms


Slide 37

Algorithms

� Algorithm – A set of steps that outline how to solve a problem.


Slide 38

Algorithms � Algorithm for DistancePtTwo Class

1.  Set class template 2.  Initialize our variables 3.  Initialize our scanner 4.  Prompt end user to enter our needed

values 5.  Calculate the total distance 6.  Output total distance


Slide 39

Numeric Expressions


Slide 40

Numeric Expressions � A numeric expression contains at least

one operand (a value or primitive variable), and my contain operators.


Slide 41

Numeric Expressions � Our Operators –

�  + : addition �  - : subtraction �  / : division �  % : modulus division (the remainder) �  * : multiplication �  = : equals �  > : greater than �  < : less than


Slide 42

Numeric Expressions � Our Operators –

�  >= : greater than or equal to �  <= : less than or equal to �  != : not equal to…


Slide 43

Chapter 4

Integer Division


Slide 44

Integer division (/) is performed when both operands are integers. Only the integer portion of the quotient is returned:

Chapter 4

Real Division


Slide 45

Real division (/) is performed when one or both operands are type double. The entire quotient, including the decimal portion is returned: double result; result = 20.0/7.0; //result is 2.857

Chapter 4

Modulus Division


Slide 46

Modulus division (%) returns the remainder of a division operation:

� 7 % 20 = 7 (zero with a remainder of seven.)

� 7 % ? = (a number between 0 and 6)

� 100 % ? = (a number between 0 and 99)


Slide 47

Chapter 4

Modulus Division

Chapter 4 Operator Precedence


Slide 48

Operators in Java have the following precedence:

1. multiplication and division

2. addition and subtraction

Operators of the same precedence are evaluated in order from left to right. For example, multiplication is performed first, then division, and finally addition:

5 + 6 * 4 / 2 = 17

Chapter 4 Changing the Order of Operations


Slide 49

The order in which operators are evaluated can be changed by using parentheses. For example, addition is performed first, then multiplication, and finally division:

(5 + 6) * 4 / 2 = 22

Practice


Slide 50

Practice


Slide 51

�  In your chapter 4 project, create a class titled: DivisionOperators � Follow along with Mr. Barrett when writing this

program. Program found on pages 83 and 84.

Practice


Slide 52

�  In your chapter 4 project, create a class titled: Digits � Page 84. � Write the digits program.

Assignment Operators


Slide 53

Chapter 4

Assignment Operators


Slide 54

Operator Operation += addition and then assignment -= subtraction and then assignment *= multiplication and then assignment /= division and then assignment %= modulus division and then assignment

Assignment Operators (+) int A = 10; int B = 5;

A += B;

System.out.print(”Our output is” +A); 15 © 2007 Lawrenceville Press

Slide 55

Assignment Operators (-) int A = 10; int B = 5;

A -= B;


Slide 56

Assignment Operators (*) int A = 10; int B = 5;

A *= B;


Slide 57

Assignment Operators (/) int A = 10; int B = 5;

A /= B;


Slide 58

Assignment Operators (%) int A = 17; int B = 5;

A %= B;


Slide 59


Slide 60

Type Casting


Slide 61

Chapter 4 Type Casting


Slide 62

Type Casting converts a number of one type to a number of a different, but compatible type. Type casting is used to:

1. make the operand types in an expression match. For example, wholeNum = (int)y * 2

2. truncate the decimal portion of a double. For example, wholeNum = (int)z

3. change the way in which a division (/) operation will be performed. For example, realDivision = (double)a / (double)b

Type Casting � Casting a double to an int truncates, or

removes, the decimal portion of the number.


Slide 63

Type Casting public class TypeCasting {

public static void main(String[] args) { int a = 2; int b = 3; int c; c=(double)a*b; System.out.print(+c); }

}


Slide 64

6.0

Type Casting: Truncating public class TypeCasting {

public static void main(String[] args) { double a = 2.2; double b = 3.1; double c; c=a*b; System.out.print(+(int)c); }

}


Slide 65

6

Programming Errors


Slide 66

Chapter 4

Programming Errors


Slide 67

§ Syntax errors violate the rules of Java.

§ look for the red (X)

§  Logic errors, also called semantic errors, occur in statements that are syntactically correct, but produce undesired or unexpected results.

§ Run-time errors, also called exceptions, halt program execution at the statement that cannot be executed. One type of exception is called InputMismatchException.

§ Look for the error that appears in your console.

Practice


Slide 68

Practice


Slide 69

�  In your chapter 4 project, create a class titled: GradeAvg1of2 � Follow along with Mr. Barrett when writing this

program. Program found on page 85.

Practice


Slide 70

�  In your chapter 4 project, create a class titled: TempConverter � Follow along with Mr. Barrett when writing this

program. Program found on page 85.

Number Formatting Class


Slide 71

Numeric Output � The NumberFormat class is used to create

objects that format numbers. � NumberFormat objects return a string that

contains a formatted number. 1.  $21.00 2.  1,342 3.  0.667 4.  33%


Slide 72

Numeric Output � The number format class allows us to

output… 1.  Money - $x.xx 2.  Number Format – xx,xxx 3.  Decimal - x.xxx 4.  Percentage - xx%


Slide 73

Numeric Output (step 1) �  Import the NumberFormating class on line

one or two of your class.

import java.text.NumberFormat


Slide 74

Numeric Output (step 2) �  Initialize the format you need to use:

1.  NumberFormat money = NumberFormat.getCurrencyInstance(); 2.  NumberFormat number = NumberFormat.getIntegerInstance(); 3.  NumberFormat decimal = NumberFormat.getNumberInstance(); 4.  NumberFormat percent = NumberFormat.getPercentInstance();


Slide 75

Numeric Output (step 3) � Prepare output statement:

1.  System.out.print(money.format(variableName)); 2.  System.out.print(number.format(variableName)); 3.  System.out.print(decimal.format(variableName)); 4.  System.out.print(percent.format(variableName));


Slide 76

Numeric Output � The number format class allows us to

output… �  Money - $x.xx - �  Number Format – xx,xxx �  Decimal - x.xxx �  Percentage - xx%


Slide 77

Practice


Slide 78

�  In your chapter 4 project, create a class titled: FormattingNumericOutput � Copy this class into your chapter 4 project.

(P 86)

Named Constants


Slide 79

Chapter 4

Named Constants


Slide 80

§ A constant is a name for a memory location that stores a value that cannot be changed from its initial assignment.

§ The keyword final is used in the variable’s declaration.

§ Constant identifiers are typically all uppercase with an underscore (_) separating words within the identifier name.

§ EX:

final int LAST_NUMBER = 100

final double PI = 3.14

Public class CircleArea{ public static void main (String[] args){ final double PI = 3.14; double radius = 5; double area;

area = PI* radius * radius; System.out.print(“The area is” +area); }

}


Slide 81

Final CH 4 Programs


Slide 82

Final CH 4 Programs � PizzaCost (p.99) � Change (p.100) � TimeConversion (p.101) � Sleep (p.101) � Spending (p.102)


Slide 83


Slide 84

Chapter 4

Java Keywords abstract double int strictfp boolean else interface super break extends long switch byte final native synchronized case finally new this catch float package throw char for private throws class goto protected transient const if public try continue implements return void default import short volatile do instanceof static While


Slide 85

Chapter 4

Flowchart Symbols


Slide 86

process

Chapter 4

The BirthdayGame Flowchart


Slide 87

Variables and Constants · Using Variables ! An assignment statement is formed with the variable...

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