object java programming - california state university...

1

Java

Programming

From Flowcharts To Java

(CSUS, Fall 2015)

Object

Oriented

Programming

Programming with "class"

This means that your

program consists of a series

of objects that will interact

with each other

An object is very abstract can

be anything

12/5/2015 Sacramento State - CSc 10A 3

Object Oriented Programming

Many objects are related to

each other – having the same

abilities and attributes

These objects belong to the

same class – which is a

classification of related

objects


Classes

A class describes what an

object will store, how it

behaves, etc…

Properties contain data about

the object

Methods describe how the

treats data (its and others)


Classes

"Cat" Class properties can include:

• name

• fur color

• breed

"Student" Class properties can include:

• name

• major

• academic level – freshman, junior, …


Example Properties

2

"Cat" Class methods:

• eat

• purr

• sleep

"Student" Class methods:

• study

• play on smart phone

• sleep


Example Methods

Classes can also "inherit" from classes

When a class inherits another:

• gets all the features of the original class

• but can extend its functionality

• allows work, created previously to become the

foundation of a more advanced class


Class Inheritance

Classes just describe the

behavior of some "object"

They don't do anything

In object-oriented

programming, you will create

instances of these classes –

i.e. objects


Instances / Objects

Instances will have all the

features of its class

So, different instances of the

same class share the same

features

But, each instance is a

different and unique


Instances / Objects

"Game" Class can have instances of:

• Pac-Man

• Call of Duty

• Fallout 4

"Food" Class can have instances of:

• ice cream

• pizza

• top ramen


Example Classes & Instances

Introduction to

Java

Start the coffee maker – seriously...

3

The Java Programming is

currently one of the most

popular languages in the

World

Java followed a long

evolutionary chain that

started with C (later C++)


What is Java?

When Java was developed,

C/C++ had been in use for

over 20 years

So, to aid programmers...

• Java syntax very close to C++

• Java has most of the same

semantics as C++


And Along Comes Java

However, Java is not

compatible with C++

It removed the low-level

features of C++

But, it will still work on

snippets of code


However, it is different

Java contains many advanced features

But, has a very symbolic syntax

• contains very few "words" - not English-like

• so, programs are not easy to read at first

It is not a beginners language

• syntax it can be intimidating

• you must type of bunch of "weird" stuff you

won't understand at first


The Result...

Structure of

Java

Programs

What the heck am I looking at?

Java programs consist of

series of class definitions

Each class contains local

variables (properties) and

functions

Each function contains its

own local variables as well as

statements


Structure of Java Programs

4

A statement will carry out a specific task

Statements are executed in order from the

first listed to the last

In Java, you can create your own and use

ones created for you


What are Statements?

Statements can be grouped together into a

block

Some types of statements…

• calls to other functions

• control – looping, etc…

• create variables


What are Statements?


Structure of a Java Program

Data about class

Used by Method

Java Data

Types

What information Java can hold

Java classes are made of

other classes or some

primitive types

Primitive types are not really

classes, but data that the

processor understands


Data in Java

Used to store whole numbers

Java has three data types

that store integers

Why three?

• more bytes you use to store a

value, the larger can be

• however, it will take more

memory


Integers

5

1

5

-100

1846

1947

-12345


Integer Examples

Data Type Range of values Bytes

byte -128 .. 127 1

short -32,768 .. 32,767 2

int-2,147,483,648 ..

2,147,483,647 4

long-9,223,372,036,854,775,808 ..

9,223,372,036,854,775,8078


Integer Data Types

Real numbers in Java are

called floating-point

Why?

• the name is based on how it is

actually stored

• the decimal place "floats

around" like it does in scientific

notation


Real Numbers

Java has two data types for

storing real numbers

Why?

• again, you might need to use

more bytes to store larger

values

• but, it will cost more memory


Real Numbers

-6.78

3.1415

1.618

2.71828

-355.1234

1234.0


Floating-Point Examples

Note the zero!

Data Type Range of values Bytes

float

10-38 to 10+38

Both positive and negative

About 6 digits precision

4

double

10-308 to 10+308

Both positive and negative

About 15 digits precision

8


Floating Point Data Types

6

Used to store letter individual

letters, digits, symbols, etc…

These are the keys you have

on your keyboard

In Java, chars are delimited

by single quotes (also called

apostrophes)


Character Data Type

'A'

'4'

' '

'$'

'&'

'^'


Character Examples

Space

Characters are combined

(into arrays) to form strings

Java denotes a string literal

with double quotes

These are stored using a

class – so a String is not a

primitive data type


Strings

"Sac State"

"Computer Science"

"Joe Gunchy"

"Hornet"

"1947"

"Cheese"


Examples of Strings

Often you want to add a control character do your program

Java has help escape sequences start with a backslash

This is followed by another character that represents the control character


Java Escape Sequences

NUL SOH STX ETX EOT ENQ ACK BEL BS HT LF VT FF CR SO SI

DLE DC1 DC2 DC3 DC4 NAK SYN ETB CAN EM SUB ESC FS GS RS US

sp ! " # $ % & ' ( ) * + , - . /

0 1 2 3 4 5 6 7 8 9 : ; < = > ?

@ A B C D E F G H I J K L M N O

P Q R S T U V W X Y Z [ \ ] ^ _

` a b c d e f g h i j k l m n o

p q r s t u v w x y z { | } ~ DEL


Important Control Characters

7


Adding characters you can't type

Code Value Description

\a 7 Alert (Bell)

\b 8 Backspace

\t 9 Tab

\n 10 New Line (Line Feed)

\v 11 Vertical tab

\f 12 Form feed (new printer page)

\c 13 Carriage return

Code Description

\" Double quote. Allows double quotes inside string literals.

\'Single quote. Allows you to define a single quote in a

character literal.

\\ Slash. Allows a slash (since it is used for special codes)

\xhh Any character with hexadecimal value hh


Some Convenient Codes

Used to store either a true or false value

These are used with Boolean-Expressions

to store flags

This is just how you did it in pseudocode

and Flowgorithm


Boolean Data Type

Java

Identifiers

Using Memory for Data

Java identifiers use the same

de-facto standard used by

most languages

They start with letter followed

by a series of letters,

numbers, or underscores

No spaces


Identifier Rules: Format

Identifiers are case sensitive

Uppercase letters do not

match lowercase letters

e.g. Result is NOT the same

as result


Identifier Rules: Case Sensitive

8

Identifiers cannot be any of

Java's 50 reserved words

and 3 reserved values

So, there are actually 53

reserved words (although

Java books insist on 50)

These have a special

meaning in the Java syntax


Identifier Rules: Reserved

abstract default goto package this

assert do if private throw

boolean double implements protected throws

break else import public transient

byte enum instanceof return true

case extends int short try

catch false interface static void

char final long strictfp volatile

class finally native super while

const float new switch

continue for null synchronized


Reserved Words of Java

x

evilMonkey

totalCost

test4


Some Valid Variable Names

first-name

1040Form

test 4

break


Some invalid Variable Names

Dash – Not Valid

Starts with a

number

A space

keyword

Over the years, a de-facto

standard emerged

Identifiers should be written in

all camel case

Put constants in all capital

letters


Identifier De-facto Standard

Java Variable

Declaration

Using Memory for Data

9

The syntax used, by Java, to

declare variables is incredibly

terse

It basically consists of …

• data type name (int, float, ...)

• followed by the identifier


Java Variable Declaration

type name ;


Variable Declaration Syntax

int, float, char, etc…

identifier


int year;

What Happens?

Memory ?

year


float pi;

What Happens?

Memory ?

pi

Storing Data

Copying data into variables

Used to change the value of

a variable

Commonly known as an

"assignment" statement

Used a lot!


Assignment Statement

10

Target = Value;


Assignment Statement Syntax

Variable you declared


int year;

year = 1947;

What Happens?

Memory:


int year;

year = 1947;

What Happens?

Memory: ?

year

?

year


int year;

year = 1947;

What Happens?

Memory 1947

Statements

What the heck am I looking at?

Each statement is followed by

a semicolon

Why?

• Java's syntax is free-flowing

• you can put multiple

statements on the same line

• or indent them on the screen


Syntax Overview

11

name ( Stuff );


Function Call Syntax

Name of function

Parenthesis

Semicolon To group statements,

Java uses curly-brackets

Sometimes, these are

also called "braces".

Both terms are correct

Java uses these for any

group of things as well


Syntax Overview

public class HelloWorld {

public static void main(String[] args) {

System.out.println("Hello, World");

}

}


Behold… Java Code


public static void main(String[] args) {


}

}


Behold… Java Code

Creates a class

Start of program

Output text

Documenting

Your Code

Actually, very important to do!

Java is very terse and cryptic

It is very easy to forget what

your code actually does by

looking at it

Remember, you might come

back to your programs years

after you wrote it


Documenting Your Code

12


Documenting Your Code

Java allows you to insert your comments

into a program

Basically, Java ignores all comments – so

they don't affect your program in any way

They start with /* and end with */

They can also span several lines

/* ... */


Comment Syntax

Anything you want

/* My first program */



Comments are helpful

Ah, that helps!

It is common to put a comment after a

statement

So, Java also permits a line comment

They start with // and take the rest of the

line


Line Comments

// ...


Comment Syntax

That's a bit shorter

// My first program



Comments are helpful

Line comment

13

Java ignores all spaces that are not inside single

or double quotes

This is called whitespace – since it appears blank

on a page of paper (or screen)

Since whitespace is ignored

• programmers use it to format programs for readability

• basically, they indent statements inside a block

• this is similar to how we display outlines

• not only is it a good idea, I will enforce it


Whitespace

Indent each statement in a

block

• normally 3 or 4 spaces are used

• some people prefer to use the tab

• … but the tab can be problematic.

A tab is displayed as a couple

spaces, but the number varies on

different editors.


Formatting guide

Put one statement per line

• Java allows you to put multiple

statements one a single line

• … but it can get confusing

Comments are your friend

• add comments tell yourself (or

a reader) what you are doing

• also good to save who edited

the file and when


Formatting guide


public HelloWorld {

int x = 0;


}

}


Proper Formatting

Indented!

public class HelloWorld {public HelloWorld

{int x = 0;System.out.println

("Hello, World");}}


Still Valid... Good Luck Reading

This!

Mathematical

Expressions

Wow, my computer can compute?

14

Expressions are…

• mathematical formulas

• follows the format you know

Operator Precedence

• order which operators are

computed

• practically all languages have

precedence levels


Expressions

Not all programming

languages have the same

precedence levels

They are pretty consistent for

basic algebra

So, make sure to consult the

documentation


Java vs. Other Languages

Operator Name

* Multiplication

/ Division

+ Addition

% Modulus (remainder)

- Subtraction & Unary Minus


Arithmetic Operators in Java


Precedence Levels: Basic Math

Operators Precedence Name

- Unary Minus

* / % Multiplication & Division

+ - Addition & Subtraction

Highest

Lowest

"Usual

Arithmetic

Conversions"

How Java does math - it is not "obvious"

float h;

h = 5 + (11 / 12);

System.out.println(h);


Tricky Example

15

5.0


Tricky Example Output

5.0? What happened

to the inches?

Every programming language has the

"Usual Arithmetic Conversions"

These are the rules which specify how data

is coerced when analyzing a mathematical

expression

You need to understand these or your

program may fail like the last example


How Math Works in Java

When Java looks at an operator

• result is based on the types of the operands

• it only uses the highest precision that it sees

The basic rules are:

• if either operand is a float, C will use a nice

floating point calculation

• if both operands are int, C will use a integer

calculation


Basic Rules…

float h;

h = 5 + (11 / 12);



Tricky Example

Both 11 and 12 are ints, so

Java computes 0


Java vs. Other Languages

This behavior of C can cause problems for

those not suspecting it

Other languages always use floating point

• Visual Basic

• Delphi

• Python

• Ruby

… but not Java!

Java inherited this behavior

from C

C was designed…

• to be fast

• to be portable – be able to run

on different processors without

many "issues"


Why the does Java do this?

16

Floating point calculations take more time

to compute than integer math

Many old processors

• did not have floating point math

• … but they had simulate it (really slow)

So, this was a logical choice


Why does Java do this?

float h;

h = 5 + (11.0 / 12);



Tricky Example Fixed

Now, this is a float

literal

5.916667


Tricky Example: Fixed Output

Much better!

Compound

Assignments

Java makes complex tasks easy

The x = x + 1 notation …

• is very cumbersome to write

• and, it is not at all natural

Why not have a special

notation for it?


Compound Assignments

Well, Java does!

• Java has special assignment

operators that can increment,

decrement, multiply and divide

• also made their way into Visual

Basic



17

Operator Name

+= Increment the variable

-= Decrement the variable

*= Multiply the variable

/= Divide the variable

%= Modulus the variable



x = 5;

x += 1;



Compound Increment Example

Add 1 to x

6


Compound Increment Example

Output

x = 5;

x *= 4;



Compound Multiply Example

Multiply x by 4

20


Compound Multiply Example Output

Incrementing or decrementing a variable by

1 is incredibly common

So, C offers another, even shorter, notation

for incrementing/decrementing a variable

It doesn't require a value, just the variable

name and the operator


Increment / Decrement Operators

18

Operator Name

++ Increment the variable by 1

-- Decrement the variable by 1


Increment / Decrement Operators

x += 1;

x++;


Wow, that is shortcut notation!

The same

Logical

Operators

Creating Powerful Logic

Logical operators in Java are

very odd looking

They are very symbolic – and

are not as intuitive as "and",

"or" and "not"

Don't worry... everyone gets

confused by these

In time, they will look natural


Logical Operators in Java

Operator Name Rules

&& AndTrue only if both operands are True

If either is False, the result is False

|| OrTrue if either operand is True

False if both operands are False

! NotTrue if the operand is False

False if the operand is True


Logical Operators


Java Basic Precedence Levels

7 - !

6 * /

5 + -

4 == != > >= < <=

2 &&

1 ||

Highest

Lowest

19


Calculate The Result

! (1 < 4) && 5 > 4 || ! (1 > 4)

! True && 5 > 4 || ! False

False && True || True

False || True

! False && 5 > 4 || ! True

If Statements

Allowing C to Make Decisions

This statement ...

• executes statements if the

expression is true

• can also contain a false branch

Uses blocks of statements

Found in virtually every

programming language


If Statement

if (Condition) {

Statements

}


Basic Syntax

Either True or False

Multiple

statements

age = 22;

if (age >= 21) {

System.out.println("Kegger!");

}


Example

Kegger!


Example Output

20

if ( Condition ) {

Statements

} else {

Statements

}


If Statement Syntax

Processed if the

Condition is false

int age = 20

if (age >= 21) {

System.out.println("Kegger!");

} else {

System.out.println("Milk!");

}


Else Example

Milk!


Else Example Output

Loops

Doing the same thing again and again

… and again

while(condition) {

Statements

}


While Statement Syntax

int x = 0;

while(x <= 5) {

System.out.println(x);

x++;

}


While Loop Example

21

0

1

2

3

4

5


While Loop Example Output

for (initial ; condition ; step) {

Statements

}


For Statement Syntax

executed first

executed after each

block

for(x = 1; x <= 5; x++) {

System.out.println(x);

}


Simple Loop Example

1

2

3

4

5


Simple Loop Example Output

Running Your

Program

It's showtime

Compiler

• the computer actually can't understand code

• so, this software translates it into the

processor's instructions

Interpreter

• rather than translating the code, an application

runs its own instructs to do the same thing

• Javascript, for example, is interpreted


How Programs are Executed

22


Program Compilation

Compiler100010011110

010100010111

111010001000

110000011110

010101000100

000011100010

int year;

year = 1974;

x = y + z;

Sometimes, the compiler will tell you the program has errors

Don't worry, even super-nerds get these

Common ones:

• syntax error

• non-defined error

• warnings


What? It didn't compile?

Something you wrote doesn't

follow the syntax rules of the

language

How do I fix it?

• look to see which symbol you

forgot to type

• in Java, it is common to forget

the semicolon


Syntax Error

You tried to call a function

that doesn't exist

How do I fix it?

• Java is case sensitive, make

sure you didn't use caps

• you might have forgot a letter


Not Defined Error

Not really an error, but the

compiler thinks you are being

naughty

How do I fix it?

• understand why you are being

warned, there is a good reason

• its best to have warning-free

programs


Warnings

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