Second session of Some of basic UNIX commands that are useful very frequently

Hi Folks,

In this i want to share some other UNIX/LINUX command which is useful for us very frequently.

To display list of files,directories that are available in current directly please run below command.

'ls'

If you want to see more options that are available for this command then you can run below command

ls -a - This option is used to display hidden files along with normal files.

ls -l - This option displays full details of all files and folders present in current directory. For example see below sample output of this command.

drwxr-xr-x 2 user group 4096 2011-01-06 12:06 Public
In this output, highlighted part consists total 10 fields which includes of below information:
d - means its a directory.(If it is file then this will be blank).
r - read permission for user,group,others.
w - write permission for user,group,others.
x - execute permission for user,group,others.
So, first 'rwx' means this file has all permissions for user. Next 'r-x' means this file has only read and execute permissions for group. Next 'r-x' means this file has only read and execute permissions for others.

ls -d */ - This option shows only folders present in current directory.

ls -s - This option shows files and folders present in current directory along with their sizes in blocks.

ls -lt - This option shows files in the order of their last modified time.

pwd - This option shows present working directory.

Please try these when you are free. In our next session we can discuss some other commands.

First session of Some of basic UNIX commands that are useful very frequently

Hi Folks,

In this blog i want to discuss some of basic unix/linux commands that are useful very frequently.

If you want to display total,used and free RAM of your machine in size of MB then run below command.

free -m

If you want to see more options that are available for this command then you can run below command

man free

Some of useful options in free command:

free -t - This option will also displays data containing the totals for physical memory and swap space along with RAM.

free -ms 5 - This option i.e. '-s' followed by an integer will display commands output i.e. total,used and free RAM in MB available in your machine for every 5 seconds.

watch free - Usage of this command is same as above but in an interval of 2 seconds. When you time this command and then press enter then a new screen will be opened and automatically refresh total,used and free available of RAM in KBs. If you press 'CTRL + C' then newly opened screen will be closed and you will be returned to your command ran screen.

watch -n 1 -d free - This is can be taken as advanced version of above command. Here '-d' option is for highlighting the changes in memory usage and '-n' is for interval. For example in this command '1' is followed by '-n' so, for every one second its going to display RAM usage in KB as we didn't mention '-m' option.

Please try these when you are free. In our next session we can discuss some other commands.

Some Of Basic FAQ about Core JAVA

Hi Friends,

In this blog i want to share some of basic FAQ about Core JAVA that may help you have some basic information.

1. Can multiple inheritance be achieved in Java. If yes, how?
   Answer – Yes, through implementing interfaces as we can implemente multile interfaces in a single class.
   
2. What is the basic difference between String and StringBuffer object?
   Answer - String is an immutable object. StringBuffer is a mutable object.
   
3. What is the base class for Error and Exception?
   Answer – Throwable is base class for Exception.
   
4. What is a static block?
   Answer – this is the block executed before the class initialization.
   
5. Can static methods call directly non static methods of the same class?
   Answer – No. They cannot directly call. If they need, they will have to create object.
   
6. From an overridden method of the sub class, how can you call the overridden base class method ?
   Answer – call the method by using 'super' keyword.
   
7. Can protected methods be accessed by classes in different package.
   Answer – Yes, provided they are subclasses. Otherwise no.
   
8. Can a subclass reference hold a superclass object.
   Eg: Class A, Class B.
   If B extends A. Can we say B b = new A()
   Answer – No. Viceversa is true (if A a = new B() is fine).
   
9. If a super class method is throwing an IOException, what should the overriding sub class method throw?
   Answer – It should either
   Throw the same IOException
   Throw a sub class of IOException.
   Throw nothing
   
10. What are the two ways of making a class non-extensible?
    Make the class Final
    Make the constructor private
    

Brief uses and advantages of java.util.Arrays

Hi Folks,

In this post i want to introduce you guys about one common utility class that is very helpful in sorting and searching of values in an array of any type like int,long,String etc. Simply we can state it as java.util.Arrays which is very useful in manipulating arrays such as searching,sorting and viewing all values as a list at a time without any iteration etc.

This class contains various methods to manipulate arrays of any type. For example, you have an array of string values like below

String s[] = {"hi", "ramu", "cris"};

and you want to sort these values then you don't need to write/implement any sorting algorithm instead you can simply use statement

Arrays.sort(s[]);

to sort those values. This java.util.Arrays.sort(Object[] a) method is useful to sort array of objects. Here our s[] is String type of object so we can simply use this method to sort our array.

If you want to print all the values using at a time then also you don'e need to iterate instead you can use

System.out.println(Arrays.asList(s[]);

This method java.util.Arrays.asList(T... a) is used to back the values to a List.

Like these there are many more methods by which you can easily manipulate arrays.

Hibernate With Examples: Hibernate Hello World Program

In this post i want to give some reference which is intuitive for beginners.

Hibernate With Examples: Hibernate Hello World Program