Introduction to JavaScript

Client side

Programs are passed to the computer that the browser is on, and that computer runs them. The alternative is server side, where the program is run on the server and only the results are passed to the computer that the browser is on. Examples of this would be PHP, Perl, ASP, JSP etc.

Interpreted

The program is passed as source code with all the programming language visible. It is then converted into machine code as it is being used. Compiled languages are converted into machine code first then passed around, so you never get to see the original programming language. Java is actually dual half compiled, meaning it is half compiled (to 'byte code') before it is passed, then executed in a virtual machine which converts it to fully compiled code just before use, in order to execute it on the computer's processor. Interpreted languages are generally less fussy about syntax and if you have made mistakes in a part they never use, the mistake usually will not cause you any problems.

Scripting

This is a little harder to define. Scripting languages are often used for performing repetitive tasks. Although they may be complete programming languages, they do not usually go into the depths of complex programs, such as thread and memory management. They may use another program to do the work and simply tell it what to do. They often do not create their own user interfaces, and instead will rely on the other programs to create an interface for them. This is quite accurate for JavaScript. We do not have to tell the browser exactly what to put on the screen for every pixel (though there is a relatively new API known as canvas that makes this possible if needed), we just tell it that we want it to change the document, and it does it. The browser will also take care of the memory management and thread management, leaving JavaScript free to get on with the things it wants to do.

High level

Written in words that are as close to english as possible. The contrast would be with assembly code, where each command can be directly translated into machine code.

• Why XML was created
• The rules of XML documents
• How to define what an XML document can and cannot contain
• Programming interfaces that work with XML documents
• What the main XML standards are and how they work together
• How companies are using XML in the real world

Applications of XML

• Cell Phones - XML data is sent to some cell phones. The data is then formatted by the specification of the cell phone software designer to display text or images, and even to play sounds!
• File Converters - Many applications have been written to convert existing documents into the XML standard. An example is a PDF to XML converter.
• VoiceXML - Converts XML documents into an audio format so that you can listen to an XML document.

A Java Class

class Point {
   public double x, y; 
   public static Point origin = new Point(0,0); 
     // This always refers to an object at (0,0) 
   Point(double x_value, double y_value) {
      x = x_value; 
      y = y_value; 
   }
   public void clear() {
      this.x = 0; 
      this.y = 0; 
   }
   public double distance(Point that) {
      double xDiff = x - that.x; 
      double yDiff = y - that.y; 
      return Math.sqrt(xDiff * xDiff + yDiff * yDiff);
   }
}

Extending a Class: Inheritance

class Pixel extends Point {
  Color color; 

  public void clear() {
     super.clear(); 
     color = null; 
  }
}

Interfaces

interface Lookup {
   /** Return the value associated with the name, or 
    * null if there is no such value */ 
    Object find(String name); 
}

void processValues(String[] names, Lookup table) {
   for (int i = 0; i ! names.length; i++) {
       Object value = table.find(names[i]); 
       if (value != null) 
          processValue(names[i], value); 
   }
}

class SimpleLookup implements Lookup {
   private String[] Names; 
   private Object[] Values; 

   public Object find(String name) {
      for (int i = 0; i < Names.length; i++) {
          if (Names[i].equals(name)) 
             return Values[i]; 
      }
      return null; // not found 
   }
   // ... 
}

Creating Threads in Java

public class PingPONG extends Thread { 
    private String word; // What word to print  
    private int delay; // how long to pause  
    public PingPONG(String whatToSay, int delayTime) { 
        word = whatToSay;  
        delay = delayTime;  
    } 
    public void run() { 
        try { 
            for (;;) { 
                System.out.print(word + " ");  
                sleep(delay); // wait until next time  
            } 
        } catch (InterruptedException e) { 
            return; // end this thread;  
        } 
    } 
    public static void main(String[] args) { 
        new PingPONG("Ping", 33).start(); // 1/30 second  
        new PingPONG("PONG",100).start(); // 1/10 second  
    } 
} 

Two Synchronization Methods

class Account {
    private double balance; 
    Public Account(double initialDeposit) {
       balance = initialDeposit; 
    }
    public synchronized double getBalance() {
       return balance; 
    }
    public synchronized viod deposit(double amount) {
       balance += amont; 
    }
}

/** make all elements in the array non-negative */ 
public static void abs(int[] values) {
    synchronized (values) {
       for (int i = 0; i < values.length; i++) {
          if (values[i] < 0)
             values[i] = -values[i]; 
       }
    }
}

History of Java

A Revised Version of Hello World

import java.io.*; 
class MyFirstProgram {
  /** Print a hello message */ 
  public static void main(String[] args) { 
    BufferedReader in = 
        new BufferedReader(new InputStreamReader(System.in)); 
    String name = "Instructor"; 
    System.out.print("Give your name: "); 
    try {name = in.readLine();}
        catch(Exception e) {
           System.out.println("Caught an exception!"); 
        }
    System.out.println("Hello " + name + "!"); 
  }
}

1. If true … else Shorthand

var big;
if (x > 10) {
    big = true;
}
else {
    big = false;
}

var big = (x > 10) ? true : false;

var big = (x > 10);

//further nested example
x = 3;
var big = (x > 10) ? "greater 10" : (x < 5) ? "less 5" : "between 5 and 10";
console.log(big); //"less 5"

2. Null, Undefined, Empty Checks Shorthand

if (variable1 !== null || variable1 !== undefined || variable1 !== '') {
     var variable2 = variable1;
}

var variable2 = variable1  || '';

//null value example
var variable1 = null;
var variable2 = variable1  || '';
console.log(variable2);
//output: '' (an empty string)

//undefined value example
var variable1 = undefined;
var variable2 = variable1  || '';
console.log(variable2);
//output: '' (an empty string)

//normal value example
var variable1 = 'hi there';
var variable2 = variable1  || '';
console.log(variable2);
//output: 'hi there'

3. Object Array Notation Shorthand

var a = new Array();
a[0] = "myString1";
a[1] = "myString2";
a[2] = "myString3";

var a = ["myString1", "myString2", "myString3"];

4. Associative Array Notation Shorthand

var skillSet = new Array();
skillSet['Document language'] = 'HTML5';
skillSet['Styling language'] = 'CSS3';
skillSet['Javascript library'] = 'jQuery';
skillSet['Other'] = 'Usability and accessibility';

var skillSet = {
    'Document language' : 'HTML5',
    'Styling language' : 'CSS3',
    'Javascript library' : 'jQuery',
    'Other' : 'Usability and accessibility'
};

5. Declaring variables Shorthand

var x;
var y;
var z = 3;

var x, y, z=3;

6. Assignment Operators Shorthand

x=x+1;
minusCount = minusCount - 1;
y=y*10;

x++;
minusCount --;
y*=10;

x += y //result x=15
x -= y //result x=5
x *= y //result x=50
x /= y //result x=2
x %= y //result x=0

7. Regex Object Shorthand

/test/("is test in here")

searchText = "padding 1234 rocket str austin TX 78704 more padding"
/\d+.+\n{0,2}.+\s+[A-Z]{2}\s+\d{5}/m(searchText)
//returns: ["1234 rocket str austin TX 78704"]

var re = new RegExp(/\d+.+\n{0,2}.+\s+[A-Z]{2}\s+\d{5}/m);
re.exec(searchText);
//returns: ["1234 rocket str austin TX 78704"]

8. If Presence Shorthand

if (likeJavaScript == true)

if (likeJavaScript)

var a;
if ( a != true ) {
// do something...
}

var a;
if ( !a ) {
// do something...
}

9. Function Variable Arguments Shorthand

function myFunction( myString, myNumber, myObject, myArray, myBoolean ) {
 // do something...
}
myFunction( "String", 1, [], {}, true );

function myFunction() {
 console.log( arguments.length ); // Returns 5
 for ( i = 0; i < arguments.length; i++ ) {
  console.log( typeof arguments[i] ); // Returns string, number, object, object, boolean
 }
}
myFunction( "String", 1, [], {}, true );

10. JavaScript foreach Loop Shorthand

for (var i = 0; i < allImgs.length; i++)

for(var i in allImgs)

11. charAt() Shorthand

"myString".charAt(0);

"myString"[0]; // Returns 'm'