Java Fundamentals Asserting Java - PowerPoint Presentation

Slide1

Java Fundamentals

Asserting Java

Chapter 2: Introduction to Computer Science

©Rick MercerSlide2

Outline

Distinguish the syntactical parts of a program

Tokens: special symbols, literals, identifiers,

Output with System.out.println

An executable program as a Java class with a

main

method

Introduce two of Java's primitive types:

int

and

doubleSlide3

Preview: A Complete Java program

import

java.util.Scanner;

// Read number from user and then display its squared value

public

class

ReadItAndSquareIt {

public

static

void

main(String[] args) {

double

x;

double

result = 0.0;

Scanner keyboard =

new

Scanner(System.

in

);

// 1. Input

System.

out

.print(

"Enter a number: "

);

x = keyboard.nextDouble();

// 2. Process

result = x * x;

// 3. Output

System.

out

.println(x +

" squared = "

+ result);

}

}Slide4

Programs have 4 types of tokens

The Java source code consists of

special symbols

+ < = >= && ||

identifiers

customerName totalBill n

reserved identifiers

int while if void

literals

123 "A String" true

These tokens build bigger things like variables, expressions, statements, methods, and classes.

Also, comments exist for humans to read

// Document your code if it is unreadable :-(Slide5

Overloaded Symbols

Some special symbols are operators and have different things in different contexts

with two integers, + sums integers

2 + 5

evaluates to the integer 7

with two floating point literals, + sums to floating point (types make a difference)

2.0 + 5.0

evaluates to 7.0

with two strings, + concatenates

"2" + "5"

evaluates to the new string

"25"Slide6

Identifiers

An

identifier

is a collection of certain characters that could mean a variety of things

There are some identifiers that are Java defines:

sqrt String Integer System in out

We can make up our own new identifiers

test1 lastName dailyNumber MAXIMUM $A_1Slide7

Valid identifiers

Identifiers have from 1 to many characters:

'a'..'z', 'A'..'Z', '0'..'9', '_', $

Identifiers start with letter

a1

is legal,

1a

is not

can also start with underscore or dollar sign:

_ $

Java is case sensitive.

A

and

a

are different

Which letters represent valid identifiers?

a)

abc

d)

$$$

i)

a_1

b)

m/h

e)

25or6to4

j)

student Number

c)

main

f)

1_time

k)

String

Slide8

Reserved Identifiers (keywords)

A

keyword

is an identifier with a pre-defined meaning that can't be changed

it's reserved

double

int

Other Java reserved identifiers

not a complete list

boolean

default for new

break do if private

case double import public

catch else

instanceOf

return

char extends

int

void

class float long whileSlide9

Literals -- Java has 6

Floating-point literals

1.234 -12.5 1.2 3. .4 1e10 0.1e-5

String literals

"characters between double quotes" "'10" "_"

Integer literals

(

Integer.

MIN_VALUE

and

Integer.

MIN_VALUE

)

-1 0 1 -2147483648 2147483647

Boolean literals (there are only two)

true false

Null (there is only this one value)

null

Character literals

'A' 'b' '\n' '1' ' 'Slide10

Comments

Provide internal documentation to explain program

Provide external documentation with javadoc

Helps programmers understand code--including their own

There are three type of comments

// on one line, or

/*

between slash star and star slash

you can mash lines down real far, or

*/

/**

* javadoc comments for external documentation

*

@return

The square root of x

*/

public

static

double

sqrt(

double

x) Slide11

General Forms

The book uses general forms to introduce parts of the Java programming language

General forms provide information to create syntactically correct programs

Anything in yellow boldface must be written exactly as shown (

println

for example)

Anything in

italic

represents something that must be supplied by the user

The italicized portions are defined elsewhereSlide12

Output Statements

A statement, made up of tokens, is code that causes something to happen while the program runs

General Forms for three output statements

System.out.print(

expression

);

System.out.println();

System.out.println(

expression

);

Example Java code that writes text to the console

System.out.print("hello world.");

System.out.println();

// print a blank line

System.out.println("Add new line after this");Slide13

General Form: A Java program

//

This Java code must be in a file named class-name

.java

public class

class-name

{

public static void main(String[]

args

) {

statement(s)

}

}

// Example Program stored in the file HelloWorld.java

import

java.util.Scanner;

public

class

HelloWorld {

public

static

void

main(String[] args) {

Scanner keyboard =

new

Scanner(System.

in

);

System.

out

.print(

"Enter your name: "

);

String myName = keyboard.next();

// keyboard input

System.

out

.println(

"Hi Rick"

);

System.

out

.println(

"This is "

+ myName);

}

}Slide14

Primitive Numeric Types

Type

: A set of values with associated operations

Java has many types, a few for storing numbers

Stores integers in

int

variables

Store floating-point numbers in

double

variables

A few operations for numeric types

Assignment

Store a new value into a variable

Arithmetic

+

,

-

,

*

(multiplication),

and

/Slide15

Variables to store numbers

To declare and give initial value:

type identifier

=

initial-value

;

Examples

int creditsA = 4;

double gradeA = 3.67;

String name = "Chris";

int hours = 10;

boolean ready = hours >= 8;Slide16

Assignment

We change the values of variables with assignment operations of this general form

variable-name

=

expression

;

Examples:

double x;

// Undefined variables

int j;

// can not be evaluated

j = 1;

x = j + 0.23;Slide17

Memory before and after

The primitive variables

x

and

j

are undefined at first

Variable Initial Assigned

Name Value Value

j ? 1

x ? 1.23

The expression to the right of

=

must be a value that the variable can store

assignment compatible

x = "oooooh nooooo, you can't do that";

// <-Error

j = x;

// <-Error, can't assign a float to an int

?

means undefinedSlide18

Assignment

double bill;

What is value for

bill

now? _________

bill = 10.00;

bill = bill + (0.06 * bill);

What is value for bill now? ________

Which letters represent valid assignments given these 3 variable initializations?

String s = "abc";

int n = 0;

double x = 0.0;

a) s = n; e) n = 1.0;

b) n = x; f) x = 999;

c) x = n; g) s = "abc" + 1;

d) s = 1; h) n = 1 + 1.5;Slide19

Arithmetic Expressions

Arithmetic expressions consist of operators such as

+ - / *

and operands such as

40

,

1.5

,

payRate

and

hoursWorked

Example expression used in an assignment:

grossPay = payRate * hoursWorked;

Another example expression:

5 / 9 * (fahrenheit - 32);

For the previous expression,

Which are the operators?_____

Which are the operands?_____ Slide20

Arithmetic Expressions

a numeric variable double x = 1.2;

or a numeric constant 100 or 99.5

or expression + expression 1.0 + x

or expression - expression 2.5 - x

or expression * expression 2 * x

or expression / expression x / 2.0

or (

expression)

(1 + 2.0)

Arithmetic expressions take many formsSlide21

Precedence of Arithmetic Operators

Expressions with more than one operator require some sort of precedence rules:

* /

evaluated in a left to right order

- +

evaluated in a left to right order in the absence of parentheses

Evaluate

2.0 + 4.0 - 6.0 * 8.0 / 6.0

Use (parentheses) for readability or to intentionally alter an expression:

double C, F;

F = 212.0;

C = 5.0 / 9.0 * (F - 32);

What is the current value of

C

____?Slide22

Math functions

Java’s

Math

class provides a collection of mathematical and trigonometric functions

Math.sqrt(16.0)

returns

4.0

Math.min(-3, -9)

returns

-0

Math.max(-3.0, -9.0)

returns

-3.0

Math.abs(4 - 8)

returns

4

Math.floor(1.9)

returns

1.0

Math.pow(-2.0, 4.0)

returns

16.0Slide23

int Arithmetic

int

variables are similar to

double

, except they can only store whole numbers (integers)

int anInt = 0;

int another = 123;

int noCanDo = 1.99;

// ERROR

Division with integers is also different

Performs quotient remainder

whole numbers only

anInt = 9 / 2;

// anInt = 4, not 4.5

anInt = anInt / 5;

What is

anInt

now? ___

anInt = 5 / 2;

What is

anInt

now? ___Slide24

The integer % operation

The Java % operator returns the remainder

anInt = 9 % 2;

// anInt ___

1

___

anInt = 101 % 2;

What is anInt now? ___

anInt = 5 % 11;

What is anInt now? ___

anInt = 361 % 60;

What is anInt now? ___

int quarter;

quarter = 79 % 50 / 25;

What is quarter? ___

quarter = 57 % 50 / 25;

What is quarter now? ___Slide25

Integer Division, watch out …

What is the current value of

celcius

_____?

int

celcius

,

fahrenheit

;

fahrenheit

= 212;

celcius

= 5 / 9 * (

fahrenheit

- 32);