Hello World Program in Java

The first program a beginner writes in Java is the Hello World Program. However, on many occasions, we do not take into account the details of basic syntax. In this article, we discuss the details of the Hello world program in Java.  We will be covering the topics like Hello world program, analysis of syntax, how to compile the program, and how we can execute it. So, let's begin our article. And you can contact us for your Java training. Naresh I Technologies is the number one computer training institute in Hyderabad and among the top five computer training institutes in India. Contact us anytime for your Java training. 

Hello World Program in Java

Before we start curating the details, let's first have a look at the coding and check how the basic hello world program in Java can be coded.

public class demo {

    public static void main (String[] args) {

        System.out.println( "Hello World" );

    }

}

And that’s the first program written by most of the beginners. Hence let’s analyze this program syntax in detail.

Syntax Analysis

Public class Demo {

Here through the use of the Class keyword, we have declared a new class known as Demo. We all know that Java is an object-oriented programming language (OOPS), and the whole class definition including the members must be enclosed within the curly braces. Also, we have used the public keyword, and that means the class is accessible from outside the package as well. If we make use of the other scope specifiers like Private or Protected that will affect the accessibility of the class. And that we will see in a separate blog. Please do not worry about it for now. 

Second Line: public static void main (String[] args){

This line has a method known as main(String[] args). This is the main method. It’s the actual entry point for the Java compiler. And it starts the program execution from here onward. And hence, whenever we execute a program, the first method invoked is the main method. And various other methods are invoked from inside the main method. And in all standard Java applications, we must have one main method as the program execution is triggered through it.

Let’s now discuss each word of this line.

Public: This is an access modifier. And it sets the visibility. And since it's public, the JVM can execute the main method from anywhere.

Static: This keyword makes the class static. And the main method Is declared static as we don’t need to define an object to call the main method. It gets invoked by JVM without object creation. And this saves the memory.

Void: This represents the return type of the method. The java main method never returns any value and hence it's always declared void.

Main(): This is the name of the method configured in JVM. 

String[]: This means that the main method can take in a single line argument which is of a type string array. And it's the java command line arguments. There are various other main method signatures possible. And they are:

static public void main(String[] args)

final public static void main(String[] args) 

And there are various others possible. We will discuss them in a later blog post. Please do not worry about it hence, for now.

Third line: System.out.println(“Hello World”);

system: This is in Java.lang package, and is a pre-defined class that has various variables and methods.

out: This is of type Printstream and is a static member field.

println: This method is in PrintStream class and we use it for printing the arguments which are passed to the console, and it also prints a newline. You can omit this and use the print() method if you do not want a newline.

We can also make use of System.exit() here. And if we pass 0 to the exit method, it means successful termination. And 1 means unsuccessful termination.  This is available in java.lang package.

And that completes our analysis of our first Java program. Let's now discuss how we can compile the Hello world Java program.

Compiling the Program

You first require to type this program in a text editor and save it. The file name will be the class name that you have mentioned in your program... Here it will hence be demo.java.

And in the next step, we need to open the console window, and then we need to navigate to the directory where the program is saved.  For compiling the program we need to make use of the command:

javac demo.java

You need to understand that java is case sensitive, and hence make sure that you are typing the file name in correct format.

If the program is executed successfully, then a demo.class file gets generated, and this is independent of the machine and also portable by nature.

And now that we have done the program compilation successfully, we need to execute the Hello world program in Java for getting the output.

Executing the Program

For executing the Hello World java program via the command line, we require typing the below code, which is 

java demo

Congratulations, you have executed your first Java program successfully. 

If you are using any IDE, you can omit all these steps, and just tap on execute button there, and execute your first java program.

And that finishes our article on the first program written by any beginner in Java. If you want to learn more you can join our Java course. And for that, you can contact us anytime and from anywhere in the world.

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Introduction:

1. As we know that the Python is more powerful language which offer great tools for data crunching and preparation, as well as for complex scientific data analysis and modelling. 

2. Python today has multiple implementations including Jython, scripted in Java language for Java Virtual Machine.

3. IronPython is the new variety which is written in C# for the Common Language Infrastructure, and PyPy version written in RPython and translated into C. 

4. Most of the Python modules work on community development model and are open-source and free.

What is the use of self in Python?

1. In Python the self is used to represent the instance of the class. 

2. Using this keyword, we can be able to access the attributes and methods of the class.

3. It is also used for binding the attributes with the given arguments. 

4. It is more often called as self because the Python does not use the '@' syntax to refer to instance attributes.

5. Here in Python, if we need to access the methods which is used to passed the instances value automatically then we can use this technique.

6. This method does not used to receive the values of the instances automatically.

Let us consider the following example below which will let you know about the use of self in detailed manner.

Here I am going to write the example which is best support for Python 3.

Example:

class car(): 

      

    # init method or constructor 

    def __init__(self, model, color): 

        self.model = model

 self.color = color 

          

    def show(self): 

        print("Model is", self.model ) 

        print("color is", self.color ) 

          

# both objects have different self which contain their attributes 

audi = car("audi a4", "blue") 

ferrari = car("ferrari 488", "green") 

  

audi.show()     # same output as car.show(audi) 

ferrari.show()  # same output as car.show(ferrari) 

Note: 

1. It should be get noted that here Behind the scenes, in every instance method call, the Python is used to sends the instances also. 

2. The Self is a convention and not a real python keyword. 

3. The self is just a parameter in function like other parameters and if the user need then they are allowed to use another parameter name in place of it if they want.

4. But as per the convention it is advisable and recommended  to use self because if we are going to use the self in the coding then it increase the readability of code.

Here I am going to write the example which is best support for Python 3.

Example:

class this_is_class:  

    def show(in_place_of_self):  

        print("we have used another " "parameter name in place of self")  

          

object = this_is_class()  

object.show() 

 Python class self-Constructor:

As you know that the Python released version 3.0 which is also called as Python 3 on December 2008. Technically this version was mainly released in order to fix the major problems which are get found in Python 2. As you know that the Python 3 was incompatible with Python 2 in many aspects. It is backward incompatible and Some features of Python 3 have been backported to Python 2.x versions to make the migration process easy in Python 3.

1. Constructors are generally used for instantiating an object.

2. It is mainly used  to initialize(assign values) to the data members of the class.

3. When an object of class is created then the members are to be get initialised using the constructor.

4. In Python the __init__() method is called the constructor and is always called when an object is created.

Let us consider the following example which will let you know how the zip function is get applied in Python3.

Syntax:

def __init__(self):

    # body of the constructor

Example:

class Person: 

  

    # default constructor 

    def __init__(self): 

        self.name = "Smith"

   # a method for printing data members 

    def print_name(self): 

        print(self.name)

# creating object of the class 

obj = Smith() 

  

# calling the instance method using the object obj 

obj.print_name()

Is self in Python a Keyword?

As we have already discussed earlier above that the self is basically used in different places as a parameter to a function. But it is not a keyword.

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Achieving your dream goal is our motto. Our excellent team is working restlessly for our students to click their target. So, believe on us and our advice, and we assured you about your sure success.

Introduction:

As we have already discussed earlier that The Python is more powerful language which offer great tools for data crunching and preparation, as well as for complex scientific data analysis and modelling. Python is a popular programming language. It was created by Guido van Rossum, and released in 1991. It is basically used for:

• web application development (server-side),

• software development,

• mathematics,

• system scripting.

Being the programmer in python Everyone should know about linked lists and its operation. A python developer should know how to create and implement the variety of linked list in practical manner. Here I am going to discuss the various ways of implementing the linked list in python using the suitable methods. 

Most of the programmer during the programming always come across a common question such as, “Does Python have a built-in or ‘native’ linked list data structure?” or, “How do I write a linked list in Python?”. Here I am going to discuss the various approaches in detail.

1. The Python language doesn’t ship with a built-in linked list data type in the “classical” sense. 

2. The Python’s list type is implemented as a dynamic array as it has the concept of list, tuple and dictionary.

3. So we need here a typical scenarios to use a “proper” linked list data structure for performance reasons.

What is Linked List? And What are their characteristics?

A linked list is mainly defined as an ordered collection of values. In python the list is used to be get created in similar way like other programming language. In python  the Linked lists are get created in similar to arrays in the sense that they contain objects in a linear order. But they are get differ from traditional arrays approach in their memory layout.

The link list is a sequence of nodes having a similar data type, each node contains one data object and pointer to the next node.

A linked list is a linear data structure with the collection of multiple nodes. Where each element stores its own data and a pointer to the location of the next element. The last link in a linked list points to null, indicating the end of the chain. An element in a linked list is called a node. The first node is called the head. The last node is called the tail.

As we know that the Arrays are contiguous data structures which stores the similar kind of element under a single name  and they’re composed of fixed-size data records stored in adjoining blocks of memory.

The arrangement of the array is looks like as showed below.

In the similar way the Linked lists is also get created.  The linked list are made up of data records linked together by pointers. This means that the data records that hold the actual “data payload” can be stored anywhere in memory. The following diagram showed below shows the  implementation scenario of linked list.

There are two different kinds of linked lists: singly-linked lists and doubly-linked lists. The diagram showed above is the singly-linked list where each element in it has a reference to (a “pointer”) to the next element in the list.

Where as in a doubly-linked list, each element has a reference to both the next and the previous element. Why is this useful? Having a reference to the previous element can speed up some operations, like removing (“unlinking”) an element from a list or traversing the list in reverse order.

As you know that the Python 3.6 (CPython), doesn’t able to provide a dedicated linked list data type. 

Python does however include the collections.deque class which provides a double-ended queue and is implemented as a doubly-linked list internally. 

Now the main question get arises that how to create and write the linked list program in python. Here I am going to discuss below.

How to write a linked list program using Python?

If you want to stick with functionality built into the core language and into the Python standard library you have two options for implementing a linked list:

• You could either use the collections.deque class from the Python standard library and take advantage of the fact that it’s implemented as a doubly-linked list behind the scenes. 

• Alternatively, you could define your own linked list type in Python by writing it from scratch using other built-in data types. You’d implement your own custom linked list class or base your implementation of Lisp-style chains of tuple objects.

Implementing a Linked List

For creating a Linked List, we create a node object and create another class to use this node object.
Code for creating Node class.
The above program creates a linked list with three data elements.

class Node(object):

# Constructor to initilize class variables

def __init__(self, data=None, next_node=None):

self.data = data

self.next_node = next_node

#get data

def get_data(self):

return self.data

# get next value

def get_next(self):

return self.next_node

# set next data

def set_next(self, new_next):

self.next_node = new_next

When we are going to implement  the linked list then the Implementation of link list consists of the following

functionality in a linked list
1. Insert: This method is basically used to insert a new node in an existing linked list.
2. Size: This method is basically used to return the size of the linked list that how many elements does it contains.
3. Search: This method will return a node containing the data, else will raise an error
4. Delete: This method will delete a node containing the data, else will raise an error

Init method in a linked list:

This method is basically used to initialised the list with initial value. The code is as showed below.

class LinkedList(object):

def __init__(self, head=None):

self.head = head

Insertion of element into the linked list:

To insert the code into the linked list we need to use the following code. The segment of the program is as discussed below.

def insert(self, data):

new_node = Node(data) 

new_node.set_next(self.head) 

self.head = new_node

Predicting the Size of the list:

The following code is used to return the size of the list.

# Returns total numbers of node in list

def size(self):

current = self.head

count = 0

while current:

count += 1

current = current.get_next()

return count

Search the element form the list:

# Returns the node in list having nodeData, error occured if node not present

def search(self, nodeData):

current = self.head

isPresent = False

while current and isPresent is False:

if current.get_data() == nodeData:

isPresent = True

else:

current = current.get_next()

if current is None:

raise ValueError("Data not present in list")

return current

Delete the existing element from the list:

# Remove the node from linked list returns error if node not present

def delete(self, nodeData):

current = self.head

previous = None

isPresent = False

while current and isPresent is False:

if current.get_data() == nodeData:

isPresent = True

else:

previous = current

current = current.get_next()

if current is None:

raise ValueError("Data not present in list")

if previous is None:

self.head = current.get_next()

else:

previous.set_next(current.get_next())

When we are going to implement the delete method  it is used to traverses the list in the same way that search does, but in addition to keeping track of the current node, the delete method also remembers the last node is visited. When delete finally arrives at the node it wants to delete. It simply removes that node from the chain by “leapfrogging” it.

Python Linked Lists: Recap & Recommendations

We just looked at a number of approaches to implement a list in Python. You also saw some code examples of the standard operations and algorithms, for example how to reverse a linked list in-place.

You should only consider using a linked list in Python when you’ve determined that you absolutely need a linked data structure for performance reasons (or you’ve been asked to use one in a coding interview.)

In many cases the same algorithm implemented on top of Python’s highly optimized list objects will be sufficiently fast. If you know a dynamic array won’t cut it and you need a linked list, then check first if you can take advantage of Python’s built-in deque class.

Scope @ NareshIT:

1. At NareshIT’s Python application Development program you will be able to get the extensive hands-on training in front-end, middleware, and back-end technology.

2. It skilled you along with phase-end and capstone projects based on real business scenarios.

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