Week 1 Log4J/Design Patterns

Question 1

Log4J

Answer 1

is a logging tool that helps us to keep track of whats going on inside of a code.
Log4J is highly configurable, through external configurations at runtime. It views the logging process in terms of levels of priority and offers mechanism to direct logging information to a variety of destinations such as data bases, file, console, Unix Syslog

Question 2

Why log5j is better than sysout

Answer 2

Log4J is better than using sysout all the time because sysout is a synchronized method that is very costly in terms of processing. Also sysout is not a debugging tool.

Question 3

A good logging format should let you decide a couple of things

Answer 3

Level - what to log (going from worst to least bad)

• OFF
• FATAL
• ERROR
• WARN
• INFO
• DEBUG
• TRACE
• ALL

Formatting/layout - how to log

• define layout
• date time style
• can output in html format

Appenders - where to log

• log files - in a file for reference later
• console - lost of console out put

Question 4

Levels explained

Answer 4

ALL - all levels including custom levels.
TRACE - designates finer grained info event than the debug.
DEBUG - designates fine grained info events that are most useful to debut at application.
INFO -designates info messages that highlight the progress of the application a coarse grained level
WARN - designates harmful situations
ERROR - designates error events that might still allow the application to continue running.
FATAL -designates very severe events that will presumably lead the application to abort.
OFF - the highest possible rank and is intended to turn off logging.

Question 5

log4J.properties

Answer 5

where properties (logging configuration in a file) are kept.

Question 6

log4J features

Answer 6

• thread safe
• high speed optimization
• multiple appenders support
• customization
• various logging levels
• layout class

Question 7

log4J Advantages

Answer 7

• Quick debugging
• Easy maintenance
• Structured Storage

Question 8

log4J Disadvantages

Answer 8

• Slows down app

- Scrolling blindness, due to config file being too verbose.

Question 9

core objects

Answer 9

Loggers
Appenders
Layouts

Question 10

Loggers

Answer 10

Responsible for capturing logging information

• Register class to logger
• Gathers the logging info an are captured in the namespace hierarchy.

Question 11

Appenders

Answer 11

Publish the logging information to the retrospective destination also lower level object.

Question 12

Layouts

Answer 12

Styles the logging info for readability (ie time stamp.)-

Question 13

Support Core Objects

Answer 13

Level
Filters
Object Renderer
Log Manager

Question 14

Level

Answer 14

defines granularity and priority of logging info

Question 15

Filter

Answer 15

analyze and decide whether to keep the logged info. Appenders can use multiple filters . tells the Appender whether or not to print the loop to the respective destination.

Question 16

Object Renderer

Answer 16

provides the string representation of the logging information.

Question 17

Log Manager

Answer 17

read the config parameter.

Question 18

What is a Singleton?

Answer 18

ensures a class has only once instance and provides global access to it.

syntax
private static Singleton instance;

static method  to get teh unique  instance if it does not exist then we will create it. 
public  static  synchronized Singleton  getInstance(){
if (instance == null){
instance = new Singleton();
}
return instance;
}

Question 19

Factory

Answer 19

factories create an object w/o exposing creation logic to the client.

Question 20

Lambda Expressions

Answer 20

Disembody function, methods that don’t belong to a class. Lamba expressions basically express instance of functional interfaces. Lamda expressions implement the only abstract function and therefore implements functional interfaces.