Big O for java Datastructures

https://docs.google.com/spreadsheet/ccc?key=0Al4BjJlYg8vEdEdRVDBTVXV3c1R5UHNnUm5Zekl6cEE#gid=0https://docs.google.com/spreadsheet/ccc?key=0Al4BjJlYg8vEdEdRVDBTVXV3c1R5UHNnUm5Zekl6cEE#gid=0

AWT notes

Component	Event it generates
Button, TextField, List, Menu	ActionEvent
Frame	WindowEvent
Checkbox, Choice, List	ItemEvent
Scrollbar	AdjustmentEvent
Mouse (hardware)	MouseEvent
Keyboard (hardware)	KeyEvent

Listener Interface	Component
WindowListener	Frame
ActionListener	Button, TextField, List, Menu
ItemListener	Checkbox, Choice, List
AdjustmentListener	Scrollbar
MouseListener	Mouse (stable)
MouseMotionListener	Mouse (moving)
KeyListener	Keyboard

example 

public class ButtonDemo extends Frame implements ActionListener { public ButtonDemo() { Button btn = new Button("OK"); btn.addActionListener(this); add(btn); } public void actionPerformed(ActionEvent e) { String str = e.getActionCommand(); } }

Understanding Page Directives

Three Key Directives

<% @ page ..... %>
<% @ include .... %>
<% @ tag lib ... %>

Page Directive :

 format  <% @ page  attribute="value"   %>


Attributes   :

buffer


Note :

Refference:
http://www.oreillynet.com/pub/a/oreilly/java/news/jsptips_1100.html

Interesting one liners

1. A method can be defined both private an final the compiler will not throw error. Declaring a method both final and private is redundant since private methods by default cannot be overridden.

2. What happen if you declare a static method as final
Ans : Stops you from declaring a static method with the same name and parameter types in a derived class

3. "this" keyword cannot be used inside static methods/blocks

4. Static final variables will have to be initialized with the declaration and cannot be left blank

5. final variables can initialized only during declaration or in the consturctor

6. Anonymous classes do not have constructors

7. few methods in Object class are-
clone, equals,hashcode,finalize,toString, notify,notifyall,wait

8. how to call garbage collector explicitly
System.gc();

9.Difference btw Interface & Abstract
all methods in the Interface and implicitly abstract

10. How to create a deamon thread
setDeamon()

Sythetic Field

http://tns-www.lcs.mit.edu/manuals/java-api-1.1beta2/guide/innerclasses/html/innerclasses.doc.html#19265

Servelet

Life Cycle of a Servelet

a) A server loads and initializes the servlet by init () method.
b) The servlet handles zero or more client’s requests through service() method.
c) The server removes the servlet through destroy() method.

What is session tracking and how do you track a user session in servlets?- Session tracking is a mechanism that servlets use to maintain state about a series requests from the same user across some period of time. The methods used for session tracking are:

a) User Authentication - occurs when a web server restricts access to some of its resources to only those clients that log in using a recognized username and password.

b) Hidden form fields - fields are added to an HTML form that are not displayed in the client’s browser. When the form containing the fields is submitted, the fields are sent back to the server.

c) URL rewriting - every URL that the user clicks on is dynamically modified or rewritten to include extra information. The extra information can be in the form of extra path information, added parameters or some custom, server-specific URL change.

d) Cookies - a bit of information that is sent by a web server to a browser and which can later be read back from that browser.

What is Server-Side Includes (SSI)?-

Server-Side Includes allows embedding servlets within HTML pages using a special servlet tag. In many servlets that support servlets, a page can be processed by the server to include output from servlets at certain points inside the HTML page. This is accomplished using a special internal SSINCLUDE, which processes the servlet tags. SSINCLUDE servlet will be invoked whenever a file with an. shtml extension is requested. So HTML files that include server-side includes must be stored with an . shtml extension.

e) HttpSession- places a limit on the number of sessions that can exist in memory. This limit is set in the session. maxresidents property.

Q:	What are the common mechanisms used for session tracking?
A:	Cookies SSL sessions URL- rewriting

Q:	What is the difference between HttpServlet and GenericServlet?
A:	A GenericServlet has a service() method aimed to handle requests. HttpServlet extends GenericServlet and adds support for doGet(), doPost(), doHead() methods (HTTP 1.0) plus doPut(), doOptions(), doDelete(), doTrace() methods (HTTP 1.1). Both these classes are abstract.
	[ Received from Amit Bhoir ]	TOP

Q:

What is the difference between ServletContext and ServletConfig?

A:

ServletContext: Defines a set of methods that a servlet uses to communicate with its servlet container, for example, to get the MIME type of a file, dispatch requests, or write to a log file.The ServletContext object is contained within the ServletConfig object, which the Web server provides the servlet when the servlet is initialized ServletConfig: The object created after a servlet is instantiated and its default constructor is read. It is created to pass initialization information to the servlet.

What is the difference between doGet() and doPost()?

#	doGet()	doPost()
1	In doGet() the parameters are appended to the URL and sent along with header information.	In doPost(), on the other hand will (typically) send the information through a socket back to the webserver and it won't show up in the URL bar.
2	The amount of information you can send back using a GET is restricted as URLs can only be 1024 characters.	You can send much more information to the server this way - and it's not restricted to textual data either. It is possible to send files and even binary data such as serialized Java objects!
3	doGet() is a request for information; it does not (or should not) change anything on the server. (doGet() should be idempotent)	doPost() provides information (such as placing an order for merchandise) that the server is expected to remember
4	Parameters are not encrypted	Parameters are encrypted
5	doGet() is faster if we set the response content length since the same connection is used. Thus increasing the performance	doPost() is generally used to update or post some information to the server.doPost is slower compared to doGet since doPost does not write the content length
6	doGet() should be idempotent. i.e. doget should be able to be repeated safely many times	This method does not need to be idempotent. Operations requested through POST can have side effects for which the user can be held accountable.
7	doGet() should be safe without any side effects for which user is held responsible	This method does not need to be either safe
8	It allows bookmarks.	It disallows bookmarks.

Creating a servelet :

1.Servlet needs to extend HttpServlet
2. Constructor calls super()
3. Has doGet() and doPost() methods
4. Web.xml has to updated with an entry for the servlet
ex :

  <servlet>
    <description></description>
    <display-name>TestServeletOne</display-name>
    <servlet-name>TestServeletOne</servlet-name>
    <servlet-class>com.cisco.capacityplanning.servelet.TestServeletOne</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>TestServeletOne</servlet-name>
    <url-pattern>/TestServeletOne</url-pattern>
  </servlet-mapping>

url for testing this servlet:

http://localhost:8080/CapacityPlanning/TestServeletOne

Singleton Class

1.Define the constructor as private
2.Expose a method that can be used to create the object - getObject()
3. Synchronize the exposed method getObject method
4. Define a private Static - which would store a single instance.

Nested Class

Todo :
1. how do nested classes act when overridden

• Non-static nested classes are also called inner classes have access to other members of the enclosing class, even if they are declared private
• Static nested classes do not have access to other members of the enclosing class
• As a member of the OuterClass, a nested class can be declared private, public, protected, or package private

Why Use Nested Classes?

There are several compelling reasons for using nested classes, among them:

• It is a way of logically grouping classes that are only used in one place.
• It increases encapsulation.
• Nested classes can lead to more readable and maintainable code.

Non Static Nested Inner Class :

To instantiate an inner class, you must first instantiate the outer class. Then, create the inner object within the outer object with this syntax:

OuterClass.InnerClass innerObject = outerObject.new InnerClass();






An instance of InnerClass can exist only within an instance of OuterClass and has direct access to the
methods and fields of its enclosing instance.

Also, because an inner class is associated with an instance, it cannot define any static members itself.


Static Nested Class :

As with class methods and variables, a static nested class is associated
with its outer class. And like static class methods, a static
nested class cannot refer directly to instance variables or
methods defined in its enclosing class — it can use
them only through an object reference.

OuterClass.StaticNestedClass nestedObject = new OuterClass.StaticNestedClass();

Types of Nested Classes

Type	Scope	Inner
static nested class	member	no
inner [non-static] class	member	yes
local class	local	yes
anonymous class	only the point where it is defined	yes

______________________________________________

Note :

1. Interfaces are never inner .
2. Non Static inner classes cannot define static variables ex static int abc =0 will result in compile time error
3. Non Static inner classes can define compile time constatns ex static final int abc=0

Connecting to Database

What are the steps involved for making a connection with a database or how do you connect to a database?

a) Loading the driver : To load the driver, Class. forName() method is used. Class. forName(”sun. jdbc. odbc. JdbcOdbcDriver”); When the driver is loaded, it registers itself with the java. sql. DriverManager class as an available database driver.

b) Making a connection with database: To open a connection to a given database, DriverManager. getConnection() method is used. Connection con = DriverManager. getConnection (”jdbc:odbc:somedb”, “user”, “password”);

c) Executing SQL statements : To execute a SQL query, java. sql. statements class is used. createStatement() method of Connection to obtain a new Statement object. Statement stmt = con. createStatement(); A query that returns data can be executed using the executeQuery() method of Statement. This method executes the statement and returns a java. sql. ResultSet that encapsulates the retrieved data: ResultSet rs = stmt. executeQuery(”SELECT * FROM some table”);

d) Process the results : ResultSet returns one row at a time. Next() method of ResultSet object can be called to move to the next row. The getString() and getObject() methods are used for retrieving column values: while(rs. next()) { String event = rs. getString(”event”); Object count = (Integer) rs. getObject(”count”);

Interface

Can you have a private variable/methods defined in an interface ?
No ( there is no point in defining a private variable/methods in the interface)

Can an interface have an abstract method defined ?
YES

Can a method in an interface be static or final
NO

Can a variable in an interface be static
YES

Setting up TOMCAT on Unix

How To Install Apache Server on your Unix Account

Following are steps to install Apachee Server in your area and you get the chance to become your own server administrator

Step 1: visit http://www.apache.org/

Step 2: Click on Apache Server (seventh item from the left).

Step 3: Click on Download.

Step 4: Click on apache_1.3.28.tar.z this the 12th item from the left and it is for Unix. Remember the place where you saved it on your PC. For the sake of explanation assume that you saved it on the desk_top. Thus on your desk_top now you have apache_1.3.28.tar.z . Notice z tells that the file is zipped and tar tells that the file is an archieve file contains more than one file.

Step 5: log in into your Unix account.

Step 6: type the following two commands to create apache directory and to make it to be the current working directory

mkdir apache

cd apache

Step 7: Use an FTP facility such as CuteFTP 32 or lite Ftp to transfer apache_1.3.28.tar.z from the desk_top to your directory in Unix. To achieve that do the following items:

a. click on the FTP facility

b. Login into your Unix account on FTP,.

c. Click on apache directory in your home directory (in FTp).

d. Click on C: then click on WINDOWS, click on desk_top, click on apache_1.3.28.tar.z on some FTP

facilities you also have to click on -->> to transfer it from desk top to your account. Now you have

apache_1.3.28.tar.z in apache directory on your home directory. Close the FTP facility.

Step 8: Make sure you are at apache directory by typing pwd command. If you are not at apache directory type

command cd apache.

Step 9: To unzip the file issue the command

gunzip apache_1.3.28.tar.z

Now the file is unzipped and if you type ls command you see you have only apache_1.3.28.tar file in apache

directory.

Step 10: To extract files from apache_1.3.28.tar type the following command:

tar xvf apache_1.3.28.tar

Notice xvf are options to tar command.

Step 11: Since files are extracted from apache_1.3.28.tar, now delete apache_1.3.28.tar file by typing:

rm apache_1.3.28.tar

Step 12: type the following command

Change directory to Apache_1.3.28 by executing

cd Apache_1.3.28

Now execute the command

./configure --prefix=/usr/users/USERDIR/apache

Notice replace USERDIR by your home director. Thus this command for user ks6241 will be:

./configure --prefix=/usr/users/students/ks6241/apache

Step 13: Type the command

make

Step 14: Type the command

make install

Step 14a: Type the command - this will save you a significant amount of disk space!

make clean

Step 15: Edit apache/conf/httpd.conf by using an editor such as pico or vi. Assume that we use pico editor, then type

pico apache/conf/httpd.conf

make the following changes while you are at pico:

Listen 3000 Notice any port number above 1000 will be fine.

Now make the following changes:

MinSpareServers 1

MaxSpareServers 2

StartServers 1

If you done every right the following message. Notice the installation takes approximately 40 minutes.

--------------------------------------------------------------------

| You now have successfully built and installed the

| Apache 1.3 HTTP server. To verify that Apache actually

| works correctly you now should first check the

| (initially created or preserved) configuration files

|

| /usr/users/cis/khailany/apache/conf/httpd.conf

|

| and then you should be able to immediately fire up

| Apache the first time by running:

|

| /usr/users/cis/khailany/apache/bin/apachectl start

|

| Thanks for using Apache. The Apache Group

| http://www.apache.org/

----------------------------------------------------------------------

After installing apache server you have to make the following changes

1. Edit 'httpd.conf' file. Assuming that you are at your home directory.

type

pico apache/conf/httpd.conf

use other path if you 'httpd.conf' is in another directory

Notice in pico control c tells in which line the editor is.

2. Comment "Listen" by using '#', since "Listen" is not being used

3. Find value "Port" (line 236) and make sure it is uncommented. The default value is '8080' which is the EMU unix web server, and therefore can not be used. Change that value to a UNIQUE value that is specific to you server.

Notice to find all port numbers which are used type the command:

netstat -a

4. Find values "User" and "Group" (line 250). Change them to your own username and group.

5. Make sure that "world" can access your apache/htdocs directory which is root directory for html web pages. In other words change the protections of apache/htdocs by typing chmod 755 apache/htdocs

6. The default cgi-bin directory is apache/cgi-bin. To change it go to line# 535 and change the value of the directory here and couple of line below to the one that you want to be your cgi-bin.

7. Close pico

8. If your apache server is running stop it by typing

apache/bin/apachectl stop

9. Restart apache by typing

apache/bin/apachectl start

Notice: If someone using your server you may not want to stop it immediately. In such cases use gracefull

command by typing

apache/bin/apachectl gracefull