BackCoding

First Java Program


Let's see what is the meaning of class, public, static, void, main, String[], System.out.println().


class :- keyword is used to declare a class in Java.

public:- keyword is an access modifier that represents visibility. It means it is visible to all.

static :- is a keyword. If we declare any method as static, it is known as the static method. The core advantage of the static method is that there is no need to create an object to invoke the static method. The main() method is executed by the JVM, so it doesn't require creating an object to invoke the main() method. So, it saves memory.

void:- is the return type of the method. It means it doesn't return any value.

main:- represents the starting point of the program.

String[]:- args or String args[] is used for command line argument. We will discuss it in coming section.

System.out.println():- is used to print statement. Here, System is a class, out is an object of the PrintStream class, println() is a method of the PrintStream class. We will discuss the internal working of System.out.println() statement in the coming section.





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Parameters used in First Java Program

Java User Input 

The Scanner class is used to get user input, and it is found in the java.util package. 

To use the Scanner class, create an object of the class and use any of the available methods found in the Scanner class documentation. In our example, we will use the nextLine() method, which is used to read Strings:


Input Types

In the example above, we used the nextLine() method, which is used to read Strings. To read other types, look at the table below:-

Method                      Description
------------------------------ ---------------------------------------------
nextBoolean()         Reads a boolean value     
                                    from the user.

nextByte()                 Reads a byte value from  
                                     the user.

nextDouble()           Reads a double value 
                                    from the user.

nextFloat()               Reads a float value from 
                                    the user.

nextInt()                  Reads a int value from      
                                    the user.

nextLine()                Reads a String value 
                                    from the user.

nextLong()              Reads a long value from 
                                    the user.

nextShort()              Reads a short value from 
                                    the user.










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How to get input from user in Java

Java Basic:
Write a Java program which accepts students name, id, and marks and display the highest score.

Output:
Roll=44
Name=Roshan
Total Marks=142
Percentage=47.33














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Java || Accepts students name, id, and marks and display the highest score

In Java, the most searching program is of employee . An employee is an entity that can have several attributes like id, name, and Selary, etc. In order to create a java employee  program, we need to create a class for the employee entity and create properties of the employees.

Output:

Enter ID:-
10
Enter name:-
Roshan
Enter Selary:-
10000





ID=10
Name=Roshan
Selary=10000.0



















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Java Program for Employee using Class and Object

Login Form Java


In Java, a form access the Login page is referred to as a Login form. A login form contains only two fields, i.e., username and password. Each user should have a unique username 

After login form, the underlying code of the form checks whether the credentials are authentic or not to allow the user to access the Login page. If the users provide unauthentic credentials, they will not be able to forward the login form.









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Java Program to Create Login Page

Definition And Usage

The this keyword refers to the current object in a method or constructor. The most common use of the this keyword is to eliminate the confusion between class attributes and parameters with the same name because a class attribute is shadowed by a method or constructor parameter

this can also be used to

Invoke current class constructor
Invoke current class method
Return the current class object
Pass an argument in the method call
Pass an argument in the constructor call

















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this keyword in Java

Loops

Loops can execute a block of code as long as a specified condition is reached.

Loops are handy because they save time, reduce errors, and they make code more readable.





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Using while loop in java || Java

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#Java #BufferedReader class is used to read the text from a character-based# input stream. It can be used to read data line by line by readLine() method. It makes the performance fast. 


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Input System in user BufferedReader class || java

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A abstract class is a class that is declared abstract—it may or may not include abstract methods. Abstract classes cannot be instantiated, but they can be subclassed.

An abstract method is a method that is declared without an implementation (without braces, and followed by a semicolon), like this:

abstract void moveTo(double deltaX, double deltaY);


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java in Object need different implementations of same method (abstract class)

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The java.util.StringTokenizer class allows you to break a String into tokens. It is simple way to break a String. It is a legacy class of #Java.

It doesn't provide the facility to differentiate numbers, quoted strings, identifiers etc. like StreamTokenizer class. We will discuss about the StreamTokenizer class in I/O chapter. 

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BufferedReader in java (StringTokenizer in Accepting Defferent Type for Input)

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Child class, we can use members of Father and Mother interface without any confusion. The height() method can be implemented in Child class to calculate child's height which we assume being the average height both of its parents.

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Multiple inheritance by Interface in Java

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getClass() is the method of Object class. This method returns the runtime class of this object. The class object which is returned is the object.

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Java Object getClass() Method

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A Factory Pattern or Factory Method Pattern says that just define an interface or class for creating an object but let the subclasses decide which class to instantiate. In other words, subclasses are responsible to create the instance of the class.


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Factory Method Pattern in java

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#Java program to add two #matrices – The following Java Code will let you know how to perform two matrix addition using Java. Soon we will add compiler to execute the Program below each method


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Java Program to multiply two matrices

write the Java programs to check if a number is positive or negative. We have used the following ways to check the number is positive, negatively


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Check if a Number is Positive or Negative||  java

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Java defines the connection between two classes that are set up through their objects. Association manages one-to-one, one-to-many, and many-to-many relationships. In Java, the multiplicity between objects is defined by the Association.



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Relationship Between Objects in java

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Finding a year is a leap or not is a bit tricky. We generally assume that if a year number is evenly divisible by 4 is a leap year. But it is not the only case. A year is a leap year if 

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Accept a Year number from the keyboard and test if is leap year in java

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Java Collection framework provides a Stack class that models and implements a Stack data structure. The class is based on the basic principle of last-in-first-out. In addition to the basic push and pop operations, the class provides three more functions of empty, search, and peek.

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Java Collection framework provides a Stack class

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An IP(Internet Protocol) address is an identifier assigned to each computer and another device (e.g., router, mobile, etc) connected to a TCP/IP network that is used to locate and identify the node in communication with other nodes on the network. IP addresses are usually written and displayed in human-readable notation such as 192.168.1.35 in IPv4(32-bit IP address).


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Java program to find IP address of Website

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Socket and ServerSocket classes are used for connection-oriented socket programming and ServerSocket classes are used for connection-less socket programming.



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Java socket programming where server sends a text and client receives and prints it.

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Java Calendar class is an abstract class that provides methods for converting date between a specific instant in time and a set of calendar fields such as MONTH, YEAR, HOUR, etc. It inherits Object class and implements the Comparable interface.



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Using Calendar Class in java (Date and Time )#shorts

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In this section, we will learn what is a luck number and also create Java programs to check if the given number is a lucky number or not. The lucky number program frequently asked in Java coding two class create first one class name Lucky and second class name MainClass .

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Lucky Number in Java

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Palindrome number in java: A palindrome number is a number that is same after reverse. For example 545, 151, 34543, 343, 171, 48984 are the palindrome numbers. It can also be a string like LOL, MADAM etc.


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Palindrome Program in Java

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Let's see the prime number program in java. In this java program, we will take a number variable and check whether the number  is prime or not ⬆️ program.

Prime number in Java: Prime number In other words, prime numbers 

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Prime Number Program in Java

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In Java programming, we often required to generate random numbers while we develop applications. Many applications have the feature to generate numbers randomly, such as to verify the user many applications use the OTP. The best example of random numbers is dice. Because when we throw it, we get a random number between 1 to 6.

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Generate Random Number in Java

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ArrayList is a part of collection framework and is present in java.util package. It provides us with dynamic arrays in Java. Though, it may be slower than standard arrays but can be helpful in programs where lots of manipulation in the array is needed. This class is found in java.util package. 





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ArrayList in Java

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Since a LinkedList acts as a dynamic array and we do not have to specify the size while creating it, the size of the list automatically increases when we dynamically add and remove items. And also, the elements are not stored in a continuous fashion. Therefore, there is no need to increase the size. Internally, the LinkedList is implemented using the doubly linked list data structure. The main difference between a normal linked list and a doubly LinkedList is that a doubly linked list contains an extra pointer, typically called the previous pointer, together with the next pointer and data which are there in the singly linked list. 

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LinkedList in Java

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The HashMap class has many useful methods. For example, to add items to it, use the put() method:





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Java Program to Get key from HashMap using the value

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The Java URL class represents an URL. URL is an acronym for Uniform Resource Locator. It points to a resource on the World Wide Web

1)Protocol: In this case, http is the protocol.

2)Server name or IP Address: In this case, www.google.com is the server name.

3)Port Number: It is an optional attribute. If we write http//wwwgoogle.com/index.html/ , 80 is the port number. If port number is not mentioned in the URL, it returns -1.

4)File Name or directory name: In this case, index.html is the file name.



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Java URL Class – Learn how to Address your resources on Internet

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Hashtable is similar to HashMap which can store elements in the form of key-value pairs. But Hashtable is synchronized assuring proper results even if multiple threads act on it simultaneously We can write Hashtable class as:

we did not mention any capacity for the Hashtable. The default initial capacity of this Hashtable 

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Java Program to Get key from Hashtable  using the value

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When computing devices such as laptops, desktops, smartphones, and tablets.

using Inet Address class

Local Host Print: IP Address print 



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Internet Address Class for java

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Integers: Integers are numbers whose base value is 10. The Integer or int data type is a 32-bit signed two’s complement integer. Its value-range lies between – 2,147,483,648 (-2^31) to 2,147,483,647 (2^31 -1)

Binary Numbers: A binary number is a number expressed in the base-2 numeral. Binary consists of only 2 digits 0 and 1

Use the + Integer.toHexString() method in Java to convert integer to hexadecimal.

The Integer.toOctalString() method converts decimal to octal string. The signature of toOctalString() method is given below:



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Java Program integer number convert it into other number system

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The stack is a linear data structure that is used to store the collection of objects. It is based on Last-In-First-Out (LIFO). Java collection framework provides many interfaces and classes to store the collection of objects. One of them is the Stack class that provides different operations such as push, pop, search, etc.

In Java, Stack is a class that falls under the Collection framework that extends the Vector class. It also implements interfaces List, Collection, Iterable, Cloneable, Serializable. It represents the LIFO stack of objects. Before using the Stack class, we must import the java.util package. The stack class arranged in the Collections framework hierarchy, as shown below.


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Stack Class In Java

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  java paylist-https://youtube.com/playlist?list=PLEFbQVymq9q7Md2FspfMp_4zFKzIunWRM
Maine driven program in Java
----------------------
1) even or odd, we calculate its remainder using % operator and check if it is divisible by 2 or not. For this, we use if...else statement in Java. If num is divisible by 2 , we print num is even. Else, we print num is odd.

2)Palindrome Program in Java
Palindrome number in java: A palindrome number is a number that is same after reverse. For example 545, 151, 34543, 343, 171, 1234321 are the palindrome numbers.

3)Prime Number Program in Java
Prime number in Java: Prime number is a number that is greater than 1 and divided by 1 or itself only. In other words, prime numbers can't be divided by other numbers than itself or 1. For example 2, 3, 5, 7, 11, 13, 17.... are the prime numbers.

4) Exit program
C paylist-https://youtube.com/playlist?list=PLEFbQVymq9q7Ob-7XYNLfHyNEfXbITvsi

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Menu driven program in Java (Basic program)

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Antony and his friends plan to create an application. They decide to create a login page. Users need to register their details and login before using the application.

They need to create a login page where only the registered user can login Create a Java program to help them create a simple model for their application by getting registration details, storing them and verifying the login process.


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 Convert binary number to a decimal number
Binary numbers are numbers consisting only of 2 digits: 0 and 1. They can be expressed in the base 2 numeral system.


Decimal numbers are numbers consisting of 10 digits: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9. They can be expressed in the base 10 numeral system.

writing a Java program that will convert a binary number into decimal

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Java Program to Convert Binary Number to Decimal Number

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Java  program enhances the coding skill, logic, and looping concepts. It is mostly asked in Java interview to check the logic and thinking of the programmer. We can print a Java pattern program in different designs.a pattern program, we must have a deep knowlede.

Each program has two or more than two loops. The number of the loop depends on the complexity of pattern or logic. The first for loop works for the row and the second loop works for the column. In the pattern programs, Java for loop is widely used.


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Print Shape Number in Java

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we need to create a binary search tree, insert a node from the tree, and display the nodes of the tree by traversing the tree using in-order traversal.

In Binary Search Tree, all nodes which are present to the left of root will be less than root node and nodes which are present to the right will be greater than the root node.

insert() will insert the new value into a binary search tree:

It checks whether root is null, which means tree is empty. New node will become root node of tree.
If tree is not empty, it will compare value of new node with root node. If value of new node is greater than root, new node will be inserted to right subtree. Else, it will be inserted in left subtree.

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Java program to construct a Binary Search Tree and perform insert and In-order traversal

binomial coefficients are the positive integers that occur as coefficients in the binomial theorem. Commonly, a binomial coefficient is indexed by a pair of integers n ≥ k ≥ 0 and is written is the coefficient of the xk term in the polynomial expansion of the binomial power (1 + x)n; this coefficient can be computed by the multiplicative formula.

formula : n!/k!(n-k)!


For example, (x+y)3=1⋅x3+3⋅x2y+3⋅xy2+1⋅y3, and the coefficients 1, 3, 3, 1 form row three of Pascal's Triangle. For this reason the numbers (nk) are usually referred to as the binomial coefficients.

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Binomial Coefficient in Java

The idea is to check whether the last bit of the number is set or not. If last bit is set then the number is odd, otherwise even.
As we know bitwise AND Operation of the Number by 1 will be 1, If it is odd because the last bit will be already set. Otherwise, it will give 0 as output

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Java Program to Check Whether a Number is Even or Odd ( bit manipulation)

Link to the github:https://github.com/Back-Coding/Sum-of-natural-numbers-using-recursion/blob/master/Recusion.java
vscode the IDE used in this video:https://code.visualstudio.com/
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Sum of natural numbers using recursion

Selection sort is a simple and efficient sorting algorithm that works by repeatedly selecting the smallest (or largest) element from the unsorted portion of the list and moving it to the sorted portion of the list. The algorithm repeatedly selects the smallest (or largest) element from the unsorted portion of the list and swaps it with the first element of the unsorted portion. This process is repeated for the remaining unsorted portion of the list until the entire list is sorted. One variation of selection sort is called “Bidirectional selection sort” which goes through the list of elements by alternating between the smallest and largest element, this way the algorithm can be faster in some cases.

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Selection Sort in Java

GitHub link 🔗:- https://github.com/Back-Coding/Marge-Sort-Algorightm/blob/master/MargeSort.java
vscode the IDE used in this video:https://code.visualstudio.com/
Merge sort is divide and conquer approach to sort the elements. It is one of the most popular and efficient sorting algorithm. It divides the given list into two equal halves, calls itself for the two halves and then merges the two sorted halves. We have to define the merge() function to perform the merging.

The sub-lists are divided again and again into halves until the list cannot be divided further. Then we combine the pair of one element lists into two-element lists, sorting them in the process. The sorted two-element pairs is merged into the four-element lists, and so on until we get the sorted list.

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Merge Sort Algorithm

GitHub link 🔗:-https://github.com/Back-Coding/Marge-Sort-Algorightm/blob/master/MargeSort.java
vscode the IDE used in this video:https://code.visualstudio.com/
Merge sort is divide and conquer approach to sort the elements. It is one of the most popular and efficient sorting algorithm. It divides the given list into two equal halves, calls itself for the two halves and then merges the two sorted halves. We have to define the merge() function to perform the merging.

The sub-lists are divided again and again into halves until the list cannot be divided further. Then we combine the pair of one element lists into two-element lists, sorting them in the process. The sorted two-element pairs is merged into the four-element lists, and so on until we get the sorted list.

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Merge Sort – Data Structure and Algorithms

The key process in quickSort is a partition(). The target of partitions is to place the pivot (any element can be chosen to be a pivot) at its correct position in the sorted array and put all smaller elements to the left of the pivot, and all greater elements to the right of the pivot.

Partition is done recursively on each side of the pivot after the pivot is placed in its correct position and this finally sorts the array.

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QuickSort – Data Structure and Algorithm

GitHub link 🔗:https://github.com/Back-Coding/Pivot-Rotated-Search-Array-DSA/blob/master/PivotRotatedSearch.java

website 🔗 link: https://www.geeksforgeeks.org/search-an-element-in-a-sorted-and-pivoted-array/


Find out the pivot point using binary search. We will set the low pointer as the first array index and high with the last array index.
From the high and low we will calculate the mid value. 
If the value at mid-1 is greater than the one at mid, return that value as the pivot.
Else if the value at the mid+1 is less than mid, return mid value as the pivot.
Otherwise, if the value at low position is greater than mid position, consider the left half. Otherwise, consider the right half.
Divide the array into two sub-arrays based on the pivot that was found.
Now call binary search for one of the two sub-arrays.
If the element is greater than the 0th element then search in the left array
Else search in the right array.
If the element is found in the selected sub-array then return the index
Else return -1.

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Java program pivot rotated search array -DSA

Website :-https://www.geeksforgeeks.org/bubble-sort/
Bubble sort works on the repeatedly swapping of adjacent elements until they are not in the intended order. It is called bubble sort because the movement of array elements is just like the movement of air bubbles in the water. Bubbles in water rise up to the surface; similarly, the array elements in bubble sort move to the end in each iteration.
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