Notes from: Introduction to Programming

This guide uses the Java language to cover programming topics.

1. Introduction to programming

Programming is important.

2. Class vs Objects

Class - is a blueprint or outline. A class manages state and behavior.
Object - is an instance of a class. An object is what lives in memory. It is the house made from the blue print.



//define a class by using "class"
class SomeClass {
    //stuff
}

//create an object by using "new"
SomeClass sc = new SomeClass();

Class constructors - "a special type of subroutine called to create an object. It prepares the new object for use, often accepting arguments that the constructor uses to set required member variables." - wikipedia
Class contructor - "a special method that is used to initialize objects. The contructor is called when an object of a class is created. It can be used to set initial values for object attributes." - w3schools

3. Constructors

Invoking the keyword new starts a process called instantiation.

Instantiation is the process of Java creating an instance of an object in memory according to the class type
Instantiation is like spawing an object. You can spawn many different houses from the same blueprint!

A constructor is a block of code that is executed when the new keyword is invoked.

The default no-arg constructor is created by the compiler if you don't write any constructors.

class A{
    //contructor
    public A(){...}
}

If you write your own constructor, then the compiler will NOT create a default no-arg constructor for you.



class SomeClass {
    int somevariable;

    public static void main(String[] args){
    ...
    }
}

its possible to overload a constructor if you specify different parameters for each constructor.

4. Encapsulation

What is Encapsulation?
Encapsulation - is the act of enclosing an item inside of a capsule or container.

In software development, encapsulation refers to the act of protecting data members from outside influence.

Data hiding is an oversimplification of the concept of encapsulation; it is partially correct.
Data hiding refers to the act of declaring member variables private, so that outside classes and other entities cannot directly access these variables.

This is a partial implementation of encapsulation, but doesnt completely describe the term in that with encapsulation you don't have to use a private modifier only.

There are others such as protected or default access levels that languages use to restrict access to data.

5. Access Modifiers

We are going to explore more about the public keyword on the main method. It is part of a group of keywords known as access modifiers. There are three of them and each controls how other classes access or call a method variable or class.

What is an access modifier? An access modifier - changes the permission levels other classes have to this method, class or variable.
An access modifier - is a keyword that you can apply to classes, methods, and instance variabels to control whether other classes are permitted to manipulate it.

There are 3 access modifiers, but there are 4 levels of access listed from least restrictive to most restrictive:

1. public - means that all classes in any package are available to call or execute this method.
   least restrictive; all classes have access
   
2. default - not an access modifier;
   only classes in the same package have access
   
3. protected - Only subclasses (in any package) have access;
   classes in same package have access as well
   
4. private - most restrictive;
   no classes (except inself) have access
   

Using an Access Modifiers

Typically, when you declare a variable or method, you'll specify an access modifier in front of it.

Classes only support the public or default level of access.

Methods and variables support all access modifiers.

Common patterns create private varaibles and public accessor methods.
Rule of thumb: Use the most restrictive access level unless you absolutely need the access.

6. Inheritance

Inheritance - Gives access to the variables and methods of one class to another.

Inheritance creats an "is-a(n)" relationship between the child and parent class. But the converse is not always true.

This relationship is one-way. All magazines are books, but not all books are magazines.

If one object is an example or a subtype of another object, the two can likely be arranged as an inheritance relationship.

For example:

• a tiny home (child class) is-a type of house (parent class).
  
• an apple (child class) is-a type of fruit (parent class).
  
• a warrior (child class) is-a type of hero (parent class).
  
• a square is-a type of rectangle.
  

A class in Java can only extend on other class.

7. Polymorphism

Polymorphism means many forms and reffers to the is-a relationship between two objects create by ineritance.

Is-A(n) Relationships

When one class extends another, an instance of that child class is also an instance of the parent class.

If one class can be described as an exmaple or subtype of another class it can probably inherit from it.

Contractual Members

A child class is guaranteed to have the public variables and methods of a super class, even if the implementations differ

This lets you write code that expects instances of a super class, but can also handle instances of child classes.

References Review

Objects are stored in heap memory, and their addresses are stored in reference variables.

reference variables use a class as a type - they can hold the address of any object that is-an instance of that class.

Dog myDog = new Dog();

Creates a new Dog object, stores the address of the Dog object in a reference variable named "myDog" that is type Dog

Reference types.
Upcasting

Method Overloading

At times you may need to have functionality in a class that supports similar types of input and output.
Instead of creating methods with really similar or unquie names, what you really need to do is employ method overloading to make your class more readable.

What is method overloading?
Method Overloading - is the creation of methods with the same name as another in the same class but it differs in parameters.

Example:
class Claculator
{
    public int add(int i, int j)
    {
        return i + j;
    }
    public double add(double i, double j)
    {
        return i + j;
    }
    public long add(long i, long j)
    {
        return i + j;
    }
}

Overridding Methods

Inheriting Methods

A method signature is the basic outline of a method:

Ex: modifiers methodName(parameters) exceptions

Any child class that you write to extend a class will inherit its methods as long as they are not marked private.

A child class can specify a new implementation for a method that is inherited.

Significance of Overriding
Overriding allows child classes to provide new implementation for their parent functionality. Useful for polymorphic references.

To override a method, you must first have a method on a parent class. In the child class, you will need to specify a mehtod of the same signature.

8. Abstraction

Abstraction - occurs when you simplify a complex thought or complex system.

When designing something, it is possible to simplfy a complex system by drawing a "black box" around the complexity and focus on the inputs and outputs of the system.
Indeed, it is sometimes helpful to break complex systems down into a network of black boxes.

The black box is an abstraction of the system.

Interfaces

An interface is a special type of construct in Java.
Used to guarantee the availability of methods in implementing classes.

All mehtods are: public abstract
All variables are public static final

Intrefaces are written similar to classes except they use the word "interface" instead of the word "class".

public interface Doable {}

public class Chore
    extends Task
    implements Doable{}

Interfaces make compiler-enforced contracts. A class that implements an interface must
A class that implements an interface must provide an implementation for every interface method, or be an abstract class
Interface methods do not have implementations and interface variables are static, so no states or behaviors are inherited

Said to have "type" inheritance. A class that implements an interface is polymorphically considered an instance of the interface.

Name interfaces for adjectives or verbs.
An interface describes what behaviors a class should have, it provides none of its own.
Ex. Runnable, Serializable, Functional

A class can implement multiple interfaces

Interfaces extend other interfaces, with no limits on the quantity allowed

Interfaces cannot extend classes, and do not implement other interfaces

Keyword:static

The static keyword determines if a method or variable belongs to the class as a whole or only an instance. What is Static?
Static - is a keyword that marks an item as a member of the class.

Recall that a class acts as a blueprint and an object is an instance of the class.

Any methods or variables that you label as static are available without having to create objects of that class type.

That main method is always labeled as static.

Keyword:final

What is Final?
Something marked final means that it cannot change its value.

If a variable is marked final, then code cannot change its value once set.

If a method is marked final, then code in subclasses cannot override it.
If a class is marked final, then another class cannot extend it.

9. Loop Statements

What is a while loop?
A while loop will repeat a block of code based on a condition; it essentially tells the program to start back up at the top from where it is defined.

while (condition)
{
    ...
}

What is a Do-while loop?
A do-while loop, will execute its statements at least once, and then continue repeating them based on a condition.

do
{
    ...
} while (condition);

10. Data Structures

Variables are not sufficient to organize data.
Data structures are used to organize data.

Arrays - a linear collection of variables of same size, and often type.
Arrays are core to most languages.

• Arrays reserve memeory so their contents are adjacent.
• Array sizes are fixed.
• Array contents are accessed by an index.
• Array indices start at 0 in almost all languages.
• Removed array elements leave an empty index.
• Arrays must always be of a fixed length and can only be specified once.

What if you don't care about memory adjacency and would like to grow or shrink the array length as needed?

Vectors or Lists are:

• flexible in size.
• Memory is not reserved at initialization.
• Often just a wrapper around an array.
• Can access elements by an index.
• Internaly doubles in size when full.
• Adding or removing elementscauses later elements to shift.

Linked Lists

• A linear collection without an index
• Made of Nodes
• A Node is a wrapper for the actual element, with a link to the element
• Accessing a particular element means searching the list
• Adding or removing an element means linking to neighbors

Maps / Dictionaries

• A collection of Nodes
• Each node wraps the element, and tracks an assigned key for that element
• The map must be able to return a node when given the approapriate key

11. Exceptions

Exceptions

• Problems that occur during compilation or execution of a program
• Exceptions are thrown and can be caught and handled independently
• Checked:
    Detected during comilation
• Unchecked:
    Occur during runtime

The throws Clause

• A method declarations can have a throws clause, indicating that it may throw and will not handle certain exceptions.
• A method with a throws clause is a source for checked exceptions.

11. SQL DB

Data Organization

• Companies need a way to quickly search records.
• Users need to be able to access records concurrently.
• Users need to always have the most recent data.
• Related data should be linked.

Relational Databases

• Link data in one table to related data in another table.
• Tables are like named spreadsheets that each track a single idea or type of record.
• Columns are the properties of each record.
• Each row is itself a record.

SQL

• A standard for database languages.
• Managed by the American national Standards Institute (ANSI).
• Databases often implement the SQL standard differently, or add to it.
• SQL is easy to read by design.
• Interaction occurs through SQL statements or "queries."

SQL Sub-Laqnguages

• DDL: Data Definition Language
  Statements that define database structure.
• DML: Data Manipulation Language
  Statements that manipulate table data.
  CRUD: Create, Read, Update, Delete.
• TCL: Transaction Control Language
  Statements that control the execution of queries.
  Transaction: A group of SQL statements executed together.

Column Datatypes

• VARCHAR: text data of variable length
• INTEGER: 32-bit, signed whole numbers
• SMALLINT: 16-bit, signed whole numbers
• NUMBER(n,d): Decimal numbers with limited significant figures
• FLOAT: floating-point numbers
• DATE: A day/month/year record
• TIMESTAMP: A combination of a date and time

Table Constraints
Column attributes that restrict data

• PRIMARY KEY: A column whose values uniquely identify each row
• Composite Key: Two or more columns acting together as a primary key
• FOREIGN KEY: A column in one table that references a column in another table
• UNIQUE KEY: A column whose values must be unique in each row
• NOT NULL: The column must have a value in each row.
• CHECK: The column values must meet some criteria

What is a join?
A Join is an operation that combines the results of two tables.

Common types of joins:

• A left join or left outer join returns the results from the frist table and records from the second table that match on a specified condition.

• A right join will return the results of the second table and records from the first only if they match records in the second based on a condition.

• An inner join will return only records from both tables that match based on a condition.

• A full join or full outer join will retrun all records from both tables.

Define and construct a simple WHERE clauses. Where clauses
Basic Sytax

A WHERE clause is appended to the end of a SELECT statement.

SELECT STATEMENT WHERE condition;

The condition indicates a column to filter and any comparison operators and values.

Ex:
SELECT * FROM EMPLOYEES WHERE
employee_id > 5;

12. HTML/CSS

HTML

• Hypertext Markup Lanuage
• Used to build webpages and provides structure
• Hypertext: content linked to related content
• Tags surround and "mark up" text, forming an element

Example of a sample HTML document:

<!DOCTYPE html>
<html>

    <head>
        <title>My First Webpage</title>
    </head>

    <body>
        <p>A paragraph</p>
    </body>

</html>

Element - a set of tags and their enclosed content. Everything higlighted is part of the element: <tag>content</tag>

Highlighted is an example of a paragraph element:
<p>We went to the park.</p>

Tags:

Highlighted is an example of a paragraph tag:
<p>We went to the park.</p>

Some tags are composed of both an opening tag and closing tag:
<tag attribute="value">content</tag>

A tag can also be a self closing tag:
<selfclosingtag/>

Attributes examples:

• <img src="logo.png" />
• <p class="first" style="color:grey">We went to the park.</p>

Tables

Webpage design naturally fits a grid system:

• <table>: the table element begins with the table tag
• <tr>: table row
• <td>: table data
• <th>: table header
• <thead>: table head
• <tbody>: table body
• <tfoot>: table footer

Lists

• <ol>: ordered list creates an itemized list.
• <ol type="a">: renders lower case letters
• <ol type="A">: renders upper case letters
• <ol type="i">: renders lower case letters Roman numerals
• <ol type="I">: renders upper case letters Roman numerals
• <ul>: unordered list creates a bulleted list.
• <li>: list item denotes an item in any kind of list.

Responsive Web Design

• Deals with designing web pages to display differently according to the device.
• Users prefer to scroll vertically than horizontally due to phones and scroll wheels.

Designing Webpages

1. Design for the smallest size first; increase afterwards.
2. Lines of text should be 8 to 10 words long.

Coding Responsive Webpages:

• Use CSS Media Queries to apply styling to different device sizes
• specify min-width property
• use relative dimensions
• Avoid @import statements

• <link rel="stylesheet" href="main.css"> :applies to all device sizes
• <link rel="stylesheet" media="(max-width:600px)" href="mobile-small.css">
• <link rel="stylesheet" media="(min-width:601px)" href="mobile-large.css">

Best Practices

• Do NOT use large fixed width elements
• Avoid the use of <table> for layout
• Use relative width values
• Use <div> for layout

CSS Syntax

Summary

• Block-style - surround portions of code in curly braces.
  
selector
{
property:value;
}

p
{
color:red;
}


• Selector - identifies what element to style.
  
• Property - identifies which component to change.
  
• Value - specifies the value of the attribute.
  
• Declaration - indicates a property/value pair.
  

CSS Selectors

Types of Selectors

• element
• class .
• id #
• all *
• multiple, elements
• parent > child
• ancestor descendant
• sibling+sibling2
• predecessor~successor

Element Selector: tagname
Selects a specific tag

• p
  {
      //apply CSS here
  }
  

Class Selectors .

• Selects all elements with the specified class attribute
• Use a . before the class name
• .purple
  {
      //apply CSS here
  }
  

ID Selectors #

• Selects all elements with the specified id attribute
• Use the pound symbol (#) before the id name
• #banner
  {
      //apply CSS here
  }
  

Universal Selector *

• Selects al elements on the page
• use the asterisk symbol (*)
• 
  {
      //apply CSS here
  }
  

Selecting Multiple Elements ,

• Selects multiple elemetns using different selectors
• Use the comma (,) to delimit multiple selectors
• html, body, p
  {
      //apply CSS here
  }
  

Parent-Child Selector >

• Selects all immediate matching children of an element
• Use the greater than symbol (>) between the parent and child
• div > p
  {
      //apply CSS here
  }
  

Ancestor-Descendant Selector

• Selects all matching descendants of an element
• Use a space ( ) between the ancestor and descendant
• div p
  {
      //apply CSS here
  }
  

Sibling Selector +

• Selects all matching siblings of an element
• Use the plus symbol (+)
• h3 + p
  {
      //apply CSS here
  }
  

Summary

• CSS offers several ways to identify which elements to apply a style to using a selector.
• You may combine selectors to further specify which elements to apply styling to.

13. JavaScript

JavaScript is a programming language that provides instructions to a web browser.

• JavaScript is NOT a server-side language. It is a scripting language.
• Is NOT related to Java
• Designed to manipulate a web page

Including JavaScript

• Use the <script>...</script> tag
• The type attribute is optional
• You can also include an external .js file <script src="file.js">...</script>

A datatype is a specialized form of information (number, string, etc.)

javaScript Datatypes

• String: represents a list of characters
    ex: "abc", '1nd*3j2n'
• Number: represents an integer or decimal value
    ex: 100, 12.0383
• Boolean: represents either true or false
    ex: true or false
• Object: represents a group of key/value pairs

ex: Cat = {
    name:'Mittens',
    age:2,
}

• Date: represents date/time
Date.now()

• Array: represents a collection of data
ex: var arr = [1,'232', 582];

• undefined: represents a value not yet defined
• null: represents an empty value

Using Variables in JavaScript

• A variable is a temporary storage unit that stores data
• var variableName;
• declaration is the process of creating a named variable

Naming Rules

1. follow camelCase convention
2. names must begin with letter, _,or $
3. numbers, and Unicode escape sequences can be used after the first character
4. names are case-sensitive:
numOfTurns is not equal to NumOfTurns

Variable Assignment

1. Use the equals sign (=) to assign a value to a variable

Variable Re-Assignment

var a;
a = 25;
a = 13; //the variable has a new value
a = 'hello'; //the variable has a new data type Re-Assigning to Null

1. To set the value of a variable to an empty value use null
var a = 23;
a = null;