Object Java Oriented Programming Programming
From Flowcharts To Java CSC10 – Spring 2016
Object Oriented Programming Classes
. Many objects are related to . This means that your each other – having the same program consists of a series abilities and attributes of objects that will interact with each other . These objects belong to the same class – which is a . An object is very abstract can classification of related be anything objects
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Classes Example Properties
. "Cat" Class properties can include: . A class describes what an • name object will store, how it behaves, etc… • fur color • breed . Properties contain data about the object . "Student" Class properties can include: • name . Methods describe how the • major treats data (its and others) • academic level – freshman, junior, …
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1 Example Methods Class Inheritance
. "Cat" Class methods: • scratch . Classes can also "inherit" from classes • purr . When a class inherits another: • sleep • gets all the features of the original class . "Student" Class methods: • but can extend its functionality • study • allows work, created previously to become the • play on smart phone foundation of a more advanced class • sleep
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Instances / Objects Instances / Objects
. Classes just describe the . Instances will have all the behavior of some "object" features of its class . They don't do anything . So, different instances of the . In object-oriented same class share the same programming, you will create features instances of these classes – . But, each instance is a i.e. objects different and unique
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Example Classes & Instances
. "Game" Class can have instances of: • Pac-Man • Call of Duty Introduction to • World of Warcraft Java . "Food" Class can have instances of: • ice cream • pizza • top ramen Start the coffee maker – seriously...
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2 What is Java? History of Java
. The Java Programming Language was created by . Java followed a long Sun Microsystems evolutionary chain that started with the C . Currently, it is one of the programming language most popular languages . C was designed by Dennis . Although Sun collapsed Ritchie at Bell Laboratories in (purchased by Oracle), Java the1970's survived
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C-riously Popular And Along Comes Java
. C became extremely popular . When Java was developed, • minimalistic C/C++ had been in use for • made efficient programs on early machines over 20 years . C++ extended the concepts of C . So, to aid programmers... • added object oriented programming • Java uses a syntax very similar • was backwards compatible... C++ could run C to C++ programs • Java as most of the same • still used today semantics as C++
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However, it is different The Result...
. Java contains many advanced features . However, Java is not . But, has a very symbolic syntax compatible with C++ • contains very few "words" - not English-like . It removed the low-level • so, programs are not easy to read at first features of C++ . It is not a beginners language . But, it will still work on • syntax it can be intimidating snippets of code • you must type of bunch of "weird" stuff you won't understand at first
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3 Structure of Java Programs
. Java programs consist of Structure of series of class definitions Java . Each class contains local variables (properties) and Programs functions . Each function contains its own local variables as well as What the heck am I looking at? statements
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What are Statements? What are Statements?
. Statements can be grouped together into a . A statement will carry out a specific task block . Statements are executed in order from the . Some types of statements… first listed to the last • calls to other functions . In Java, you can create your own and use • control – looping, etc… ones created for you • create variables
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Structure of a Java Program
Data about class Java Data Types Used by Method
What information Java can hold
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4 Data in Java Integers
. Used to store whole numbers . Java classes are made of . Java has three data types other classes or some that store integers primitive types . Why three? . Primitive types are not really • more bytes you use to store a classes, but data that the value, the larger can be processor understands • however, it will take more memory
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Integer Examples Integer Data Types
Data Type Range of values Bytes . 1 byte -128 .. 127 1 . 5
. -100 short -32,768 .. 32,767 2 . 1846 -2,147,483,648 .. int 4 . 1947 2,147,483,647
. -12345 -9,223,372,036,854,775,808 .. long 8 9,223,372,036,854,775,807
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Real Numbers Real Numbers
. Real numbers in Java are . Java has two data types for called "floating-point" storing real numbers . Why call it a float? . Why? • name is based on how it is • again, you might need to use actually stored more bytes to store larger • the decimal place is "floats values around" like it does in scientific • but, it will cost more memory notation
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5 Floating-Point Examples Floating Point Data Types
Data Type Range of values Bytes . -6.78 . 3.1415 10-38 to 10+38 float Both positive and negative 4 . 1.618 About 6 digits precision . 2.71828 . -355.1234 10-308 to 10+308 double Both positive and negative 8 . 1234.0 Note the zero! About 15 digits precision
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Character Data Type Character Examples
. Used to store letter individual . 'A' letters, digits, symbols, etc… . '4' Space . These are the keys you have . ' ' on your keyboard . '$' . In Java, chars are delimited . '&' by single quotes (also called apostrophes) . '^'
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Boolean Data Type Primitive Data Type Summary
Data Type Range of values
byte -128 .. 127 . Used to store either a true or false value short -32,768 .. 32,767 . These are used with Boolean-Expressions int -2,147,483,648 .. 2,147,483,647 to store flags long -9,223,372,036,854,775,808 .. -9,223,372,036,854,775,807 . This is just how you did it in pseudocode float 10-38 to 10+38, positive or negative, about 6 digits precision and Flowgorithm double 10-308 to 10+308 , positive or negative, about 15 digits precision char Unicode characters (generally 16 bits per char)
boolean True or false
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6 How do you store words? Examples of Strings
. What if you want to store a word? . "Sac State" • text is really just a long series of characters • so, Java implements these in memory using . "Computer Science" multiple chars called a string . "Joe Gunchy" . Java denotes a string literal with double . "Hornet" quotes . "1947" . These are stored using a class – so a . "Pac-Man" String is not a primitive data type
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Characters
. Characters are actually More on integers . Each has a unique value Characters • characters and their matching values are a "character set" • there have been many characters sets developed over How Text is Stored time
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Java Escape Sequences Java Escape Sequences
. Java has help escape . Often you want to add a sequences start with a control character do your backslash program . This is followed by another . … but you can't type them character that represents the control character
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7 Important Control Characters Adding characters you can't type
NUL SOH STX ETX EOT ENQ ACK BEL BS HT LF VT FF CR SO SI Code Value Description \a DLE DC1 DC2 DC3 DC4 NAK SYN ETB CAN EM SUB ESC FS GS RS US 7 Alert (Bell)
sp ! " # $ % & ' ( ) * + , - . / \b 8 Backspace
0 1 2 3 4 5 6 7 8 9 : ; < = > ? \t 9 Tab
@ A B C D E F G H I J K L M N O \n 10 New Line (Line Feed)
P Q R S T U V W X Y Z [ \ ] ^ _ \v 11 Vertical tab
` a b c d e f g h i j k l m n o \f 12 Form feed (new printer page)
p q r s t u v w x y z { | } ~ DEL \c 13 Carriage return
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Some Convenient Codes
Code Description \" Double quote. Allows double quotes inside string literals. Java \' Single quote. Allows you to define a single quote in a character literal. Identifiers
\\ Slash. Allows a slash (since it is used for special codes)
\xhh Any character with hexadecimal value hh Using Memory for Data
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Identifier Rules: Format Identifier Rules: Case Sensitive
. Java identifiers use the same de-facto standard used by . Identifiers are case sensitive most languages . Uppercase letters do not . They start with letter followed match lowercase letters by a series of letters, . e.g. Result is NOT the same numbers, or underscores as result . No spaces
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8 Identifier Rules: Reserved Reserved Words of Java
abstract default goto package this
. Identifiers cannot be any of assert do if private throw Java's 50 reserved words boolean double implements protected throws and 3 reserved values break else import public transient byte enum instanceof return true . So, there are actually 53 case extends int short try
reserved words (although catch false interface static void Java books insist on 50) char final long strictfp volatile . These have a special class finally native super while meaning in the Java syntax const float new switch continue for null synchronized
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Some Valid Variable Names Some invalid Variable Names
Dash – Not Valid
x first-name Starts with a evilMonkey 1040Form number
totalCost test 4 A space test4 break keyword
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Identifier De-facto Standard
. Over the years, a de-facto standard emerged Java Variable . Identifiers should be written in Declaration all camel case . Put constants in all capital letters Using Memory for Data
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9 Java Variable Declaration Variable Declaration Syntax
. The syntax used, by Java, to int, float, char, etc… declare variables is incredibly terse . It basically consists of … type name ; • data type name (int, float, ...) • followed by the identifier identifier
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What Happens? What Happens?
year pi Memory ? Memory ?
int year; float pi;
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Assignment Statement
. Used to change the value of Storing Data a variable . Commonly known as an "assignment" statement . Used a lot!
Copying data into variables
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10 Assignment Statement Syntax What Happens?
Variable you declared Memory:
Target = Value; int year; year = 1947;
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What Happens? What Happens?
year year Memory: ? Memory 1947?
int year; int year; year = 1947; year = 1947;
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Syntax Overview
. Each statement is followed by a semicolon Statements . Why? • Java's syntax is free-flowing • you can put multiple statements on the same line • or indent them on the screen What the heck am I looking at?
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11 Function Call Syntax Syntax Overview
. To group statements, Name of function Semicolon Java uses curly-brackets . Sometimes, these are name ( Stuff ); also called "braces". Both terms are correct . Java uses these for any Parenthesis group of things as well
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Behold… Java Code Behold… Java Code
Creates a class Start of program public class HelloWorld { public class HelloWorld { public static void main(String[] args) { public static void main(String[] args) { System.out.println("Hello, World"); System.out.println("Hello, World"); } } } } Output text
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Documenting Your Code
. Java is very terse and cryptic Documenting . It is very easy to forget what your code actually does by Your Code looking at it . Remember, you might come back to your programs years after you wrote it Actually, very important to do!
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12 Documenting Your Code Comment Syntax
. 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 Anything you want
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Comments are helpful Line Comments
Ah, that helps! . It is common to put a comment after a statement /* My first program */ . So, Java also permits a line comment System.out.println("Hello, World"); . They start with // and take the rest of the line
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Comment Syntax Comments are helpful
Line comment
// My first program // ... System.out.println("Hello, World");
That's a bit shorter
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13 Whitespace Formatting guide
. Java ignores all spaces that are not inside single or double quotes . Indent each statement in a block . This is called whitespace – since it appears blank on a page of paper (or screen) • normally 3 or 4 spaces are used . Since whitespace is ignored • some people prefer to use the tab • programmers use it to format programs for readability • … but the tab can be problematic. A tab is displayed as a couple • basically, they indent statements inside a block spaces, but the number varies on • this is similar to how we display outlines different editors. • not only is it a good idea, I will enforce it
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Formatting guide Proper Formatting
. Put one statement per line • Java allows you to put multiple statements one a single line public class HelloWorld { public HelloWorld { • … but it can get confusing int x = 0; . Comments are your friend System.out.println("Hello, World"); • add comments tell yourself (or } a reader) what you are doing } • also good to save who edited Indented! the file and when
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Still Valid... Good Luck Reading This!
Mathematical public class HelloWorld {public HelloWorld {int x = 0;System.out.println Expressions ("Hello, World");}}
Wow, my computer can compute?
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14 Expressions Java vs. Other Languages
. Expressions are… . Not all programming • mathematical formulas languages have the same • follows the format you know precedence levels . Operator Precedence . They are pretty consistent for • order which operators are basic algebra computed . So, make sure to consult the • practically all languages have documentation precedence levels
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Arithmetic Operators in Java Precedence Levels: Basic Math
Operator Name Operators Precedence Name * Multiplication Highest / Division - Unary Minus + Addition * / % Multiplication & Division % Modulus (remainder) - Subtraction & Unary Minus + - Addition & Subtraction Lowest
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Tricky Example
"Usual Arithmetic float h;
Conversions" h = 5 + (11 / 12); System.out.println(h);
How Java does math - it is not "obvious"
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15 Tricky Example Output How Math Works in Java
5.0 . Every programming language has the "Usual Arithmetic Conversions" . These are the rules which specify how data is coerced when analyzing a mathematical 5.0? What happened to the inches? expression . You need to understand these or your program may fail like the last example
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Basic Rules… Tricky Example
. When Java looks at an operator Both 11 and 12 are ints, so • result is based on the types of the operands float h; Java computes 0 • it only uses the highest precision that it sees . The basic rules are: • if either operand is a float, C will use a nice h = 5 + (11 / 12); floating point calculation System.out.println(h); • if both operands are int, C will use a integer calculation
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Java vs. Other Languages Why the does Java do this?
. This behavior of C can cause problems for those not suspecting it . Java inherited this behavior from C . Other languages always use floating point • Visual Basic . C was designed… • Delphi • to be fast • Python • to be portable – be able to run on different processors without • Ruby many "issues" . … but not Java!
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16 Why does Java do this? Tricky Example Fixed
. Floating point calculations take more time Now, this is a float to compute than integer math float h; literal . Many old processors • did not have floating point math h = 5 + (11.0 / 12); • … but they had simulate it (really slow) System.out.println(h); . So, this was a logical choice
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Tricky Example: Fixed Output
5.916667 Casts
Much better!
Force Java to convert data
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Typecasting Typecasting
. Java has a "cast" unary . Java computations have operator some "gotchas" • forces Java to convert one data . However, Java also gives you type to another great control on how data will • syntax uses the name of the be analyzed data type surrounded by parenthesis
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17 Okay, Let's get the Terminology Cast Operator Syntax Down…
int, float, etc… . Typecasting – when one type of data is converted to another . When the programming language converts the data implicitly, it is coerced (type) data . When the programmer explicitly specifies how data will be converted, it is cast
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Precedence Levels: with Cast Tricky Example: Using a Cast
Operators Precedence Name Now, this is a float literal ( type ) Cast Highest float h;
- Unary Minus h = 5 + (float) 11 / 12; * / % Multiplication & Division System.out.println(h);
+ - Addition & Subtraction Lowest
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Another Cast Example Cast Example Output
3.0 3.14 cast to int float pi;
pi = (int) 3.14159265; (int) converted 3.14 to System.out.println(h); 3 before assigning
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18 Compound Assignments
Compound . The x = x + 1 notation … • is very cumbersome to write Assignments • and, it is not at all natural . Why not have a special notation for it?
Java makes complex tasks easy
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Compound Assignments Compound Assignments
Operator Name
. Well, Java does! += Increment the variable • Java has special assignment -= Decrement the variable operators that can increment, decrement, multiply and divide *= Multiply the variable • also made their way into Visual /= Basic Divide the variable %= Modulus the variable
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Compound Increment Example Compound Increment Example Output
x = 5; 6
x += 1; Add 1 to x
System.out.println(h);
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19 Compound Multiply Example Compound Multiply Example Output
20 x = 5; Multiply x by 4 x *= 4; System.out.println(h);
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Increment / Decrement Operators Increment / Decrement Operators
Operator Name
. Incrementing or decrementing a variable by ++ Increment the variable by 1 1 is incredibly common . So, C offers another, even shorter, notation -- Decrement the variable by 1 for incrementing/decrementing a variable . It doesn't require a value, just the variable name and the operator
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Wow, that is shortcut notation!
x += 1; Logical
The same Operators x++; Creating Powerful Logic
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20 Logical Operators in Java Logical Operators
. Logical operators in Java are Operator Name Rules very odd looking True only if both operands are True . They are very symbolic – and && And If either is False, the result is False are not as intuitive as "and", "or" and "not" True if either operand is True || Or . Don't worry... everyone gets False if both operands are False
confused by these True if the operand is False ! Not . In time, they will look natural False if the operand is True
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Java Basic Precedence Levels Calculate The Result
7 - ! Highest ! (1 < 4) && 5 > 4 || ! (1 > 4) 6 * / ! True && 5 > 4 || ! False 5 + - ! False && 5 > 4 || ! True 4 == != > >= < <=
2 && False && True || True
1 || Lowest False || True
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If Statement
. This statement ... • executes statements if the If Statements expression is true • can also contain a false branch . Uses blocks of statements . Found in virtually every programming language Allowing C to Make Decisions
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21 Basic Syntax Example
Either True or False age = 22; if (Condition) { if (age >= 21) { Statements printf("Kegger!"); } Multiple statements }
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Example Output If Statement Syntax
Kegger! if ( Condition ) { Statements
} else { Processed if the Statements Condition is false }
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Else Example Else Example Output
int age = 20 Milk! :(
if (age >= 21) { printf("Kegger! :)"); } else { printf("Milk! :("); }
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22 While Statement Syntax
Loops while(condition) { Statements } Doing the same thing again and again … and again 5/1/2016 Sacramento State - CSc 10A 134
While Loop Example While Loop Example Output
int x = 0; 0 1 while(x <= 5) { 2 System.out.println(x); 3 x++; 4 } 5
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For Statement Syntax Simple Loop Example
executed first
for (initial ; condition ; step) { for(x = 1; x <= 5; x++) { Statements System.out.println(x); } } executed after each block
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23 Simple Loop Example Output
1 2 Running Your 3 Program 4 5 It's showtime
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How Programs are Executed Program Compilation
. Compiler • the computer actually can't understand code Compiler 100010011110 • so, this software translates it into the int year; 010100010111 year = 1974; 111010001000 processor's instructions 110000011110 x = y + z; 010101000100 . Interpreter 000011100010 • rather than translating the code, an application runs its own instructs to do the same thing • Javascript, for example, is interpreted
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What? It didn't compile? Syntax Error
. Sometimes, the compiler will . Something you wrote doesn't tell you the program has errors follow the syntax rules of the language . Don't worry, even super- nerds get these . How do I fix it? . Common ones: • look to see which symbol you • syntax error forgot to type • non-defined error • in Java, it is common to forget • warnings the semicolon
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24 Not Defined Error Warnings
. Not really an error, but the . You tried to call a function compiler thinks you are being that doesn't exist naughty . How do I fix it? . How do I fix it? • Java is case sensitive, make • understand why you are being sure you didn't use caps warned, there is a good reason • you might have forgot a letter • its best to have warning-free programs
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