Forem: Ritvik Dubey

Most Introductory React Blog Ever

Ritvik Dubey — Wed, 22 Jan 2025 19:29:15 +0000

Hello all👋 I hope you are doing well. As you have read the title you might know what is going to be in this blog but wait, maybe you don't know it or you might find something which you had no idea. So give this short article a quick read.

Story behind writing this blog

A few years ago, when I was asked about react, my answer was that it’s just js. Yes, it is js but what next what it does do? Why is everyone around talking about it?
I was looking for a very elementary article or read about React. But I didn't find anything. And even now I see many of my colleagues or my friends going through the same, so I have decided to write articles on React which help them to initiate their react journey. I'll try my level best to make these articles very easy as I have done with my java or CSS articles.
So in this article, I'll try to give you guys an overview of what actually React is, won't take you to the coding part or tough technical terms will keep it simple and complete it in a few points.
Please add something from your side in the comment section.

Let's begin...

React is a JavaScript front-end JavaScript library created by Meta (formerly Facebook). Yes, it is a library, not a framework and Angular is a framework used to create user interfaces.
To use React you simply need to install it and create your user interface. Will talk about using it in the next articles, for now just keep in mind that to use it we just install it using a simple command.
When we use React it gives us a good mobile-like experience in our web application.
When we create our web application using React we do not need to wait for another page to load on clicking over any link, button, or tab.
React does not require us to reload the page, the data gets updated on the page itself without reloading it meaning we don't use any reload() method here though there is no such restriction to not use it because at the end it is JavaScript.
Web applications created using React are highly interactive and very smooth in usage. Also, the transitions happen here pretty instantly we don't need to wait for a new page to load.
In traditional websites with a click, we send a request to the server and the server returns us an HTML page in response, so there we may have some latency and need to wait for the page to load. While in this case, we are running JavaScript in the browser so we can run our logic in the browser which allows us to manipulate what the user sees. It does so using the DOM which is actually an HTML structure. That's why we don't need to request an HTML page to show something different to the user.
The main point about React is the declarative component-focused approach. Everything in React is a component. What is a React component? A React component is a block that works like a function, we pass some parameters to it and it returns a React element.
Now the question arises what a React element is? So as we all know we have elements in HTML (p, div, body), and using those elements we create the front-end of our applications. Now a React element is used the same way we use HTML elements but these React elements are created by us and those HTML are already created.
Now the question arises that how to create React elements? So to create React elements we use JSX. JSX stands for JavaScript XML. A JSX code is basically HTML code inside of JavaScript. We are not required to use JSX but it makes it easier to write React applications. Enough introduction to JSX for now, we will have a separate article on JSX.
Now the most important point why we use React is that it uses the SPA approach, Single Page Applications approach. In this approach, no new HTML page is loaded, the server sends the HTML page once thereafter React takes over and controls the UI of the application by manipulating the DOM elements on the existing page. The best example of this is the NetFlix website, you can visit it and observe on your own that no HTML page loading takes place here.
https://www.netflix.com/

So at the end I would say React is all about building modern reactive user interfaces.

Thank you for reading. See you soon with another elementary article

Please share your thoughts about it and correct me if I'm wrong.

I hope you liked it and found it helpful.

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If you like to read about Java or CSS do visit my blog https://dev.to/ritvikdubey27

Introduction to java.util Package

Ritvik Dubey — Sun, 12 Sep 2021 10:45:39 +0000

Hello all👋 I hope you are doing well. This is going to be a short introductory article about the most useful package in Java i.e., java.util package.

Let's begin...

Let's first understand package

What is a package?

In short a Java package is collection of similar type of classes.

A Package can be defined as a collection of similar types of classes, interfaces and sub-packages in the form of directory structure. You can read more about packages in one of my article here.

java.util

The basic utility classes required to a programmer are present in this package. It contains the collections framework, legacy collection classes, event model, date and time facilities, internationalization, and miscellaneous utility classes (a string tokenizer, a random-number generator, and a bit array).

To use any class you have to import java.util package at top of the program:-

import java.util.*;

import java.util.Class_name;

To make it easy let's take an example, let's suppose you want to print date and time in your program you will need to import java.util package.

import java.util.Date;
//or
//import java.util.*;

public class Demo {
    public static void main(String[] args) {
        Date date = new Date();
        System.out.println("The date is : " + date);
    }
}

You can run your code online here

What is use of java.util package?

For Java collections.
For random number generation.
For Calendar.
For string parsing.
For internationalization support by using the internationalization supported classes from java.util package (Locale).

Some important and generally used classes

Some important and generally used classes and interfaces which are present inside the java.util package are:-

Arrays :- This class contains various methods for manipulating arrays.
ArrayList :- This class is resizable-array implementation of the List interface.
Collections :- This class consists exclusively of static methods that operate on or return collections.
Date :- This class represents a specific instant in time, with millisecond precision.
EventObject :- This class is the root class from which all event state objects shall be derived.
Formatter :- An interpreter for printf-style format strings.
HashMap :- The HashMap class Hash table based implementation of the Map interface.
HashSet :- The HashSet class implements the Set interface, backed by a hash table (actually a HashMap instance).
HashTable :- The HashTable class implements a hash table, which maps keys to values.
LinkedList :- The LinkedList class Doubly-linked list implementation of the List and Deque interfaces.
Locale :- A Locale object represents a specific geographical, political, or cultural region.
Objects :- This class consists of static utility methods for operating on objects.
Random :- An instance of this class is used to generate a stream of pseudorandom numbers.
Scanner :- A simple text scanner which can parse primitive types and strings using regular expressions. (Read more)
StringTokenizer :- The string tokenizer class allows an application to break a string into tokens.
Timer :- A facility for threads to schedule tasks for future execution in a background thread.
TimerTask :- A task that can be scheduled for one-time or repeated execution by a Timer.
TreeMap :- The TreeMap class A Red-Black tree based NavigableMap implementation.
TreeSet :- The TreeSet class A NavigableSet implementation based on a TreeMap.

Resources-

Documentation ||
Tutorial

Okay so that's enough for now.

Thank you for reading.

Please share your thoughts about it and correct me if I'm wrong.

I hope you liked it and found it helpful.

Cover:- Rajat Gour

Connect with me on Twitter or LinkedIn

My personal blog blog.ritvikdubey.com

Java indexOf() Method

Ritvik Dubey — Sun, 05 Sep 2021 12:06:59 +0000

Hello all👋 I hope you are doing well. Again this is going to be a very short and very useful article. In this article I'll be writing about indexOf() method in Java. This is a one of the most useful methods.

Let's begin...

indexOf()

This method lets you find a string within another string. The indexOf() method searches for the first occurrence of a character or substring. This method returns the index position of the first occurrence of a specified string. This is a method of Java String class. In other words, this method retrieves the index value associated with a particular character or substring in a string. If the character or phrase does not occur in the string, indexOf() returns -1.

Syntax:-

stringName.indexOf(char ch);

There are different variations in which indexOf() can be used:-

1. indexOf(char ch)

In this variation we have printed the index value of first occurrence of character i

public class Demo {
    public static void main(String[] args) {
        String str = "We will find index of i in this";
        System.out.println("Index of the character i is : " + str.indexOf('i'));
    }
}

You can run your code online here

2. indexOf(char ch, int start)

In this variation we have printed the index value of character i but not at its first occurrence, the character i first occurs at index 4, so we gave it starting value greater than 4

public class Demo {
    public static void main(String[] args) {
        String str = "We will find index of i in this";
        System.out.println("Index of the character i is : " + str.indexOf('i', 5));
    }
}

You can run your code online here

3. indexOf(String str)

In this variation we have printed the index value of first occurrence of string in

public class Demo {
    public static void main(String[] args) {
        String str = "We will find index of in here";
        System.out.println("Index of the String in is : " + str.indexOf("in"));
    }
}

You can run your code online here

4. indexOf(String str, int start)

In this variation we have printed the index value of String in but not at its first occurrence, the String in first occurs at index 9, so we gave it starting value greater than 9

public class Demo {
    public static void main(String[] args) {
        String str = "We will find index of in here";
        System.out.println("Index of the String in is : " + str.indexOf("in", 10));
    }
}

You can run your code online here

A common scenario can be when a system admin wants to find the index of the ‘@’ character of the email Id of a client and then wants to get the remaining substring. In that situation, indexOf method can be used.

Okay so that's enough for now.

Thank you for reading.

Please share your thoughts about it and correct me if I'm wrong.

I hope you liked it and found it helpful.

Cover:- Rajat Gour

Connect with me on Twitter or LinkedIn

My personal blog blog.ritvikdubey.com

Java replace() Method

Ritvik Dubey — Sun, 29 Aug 2021 12:23:01 +0000

Hello all👋 I hope you are doing well. This is going to be a very short and very useful article. In this article I'll be writing about replace() method in Java. This is a one of the most useful methods.

Let's begin...

replace()

The replace() method will replace a character or substring with another character or string. This is a method of Java String class. It returns a string derived from the original string by replacing every occurrence of old-string or old-character with new-string or new-character. When working with a string in Java, you may encounter a situation where you want to replace a specific character or substring in that string with another character or another substring. In such situations replace() method comes in.

Syntax :-

stringName.replace(oldString, newString);

There are many variations in which replace() can be used.

1. replace(char oldChar, char newChar)

In this example we have replaced all the occurrences of char ‘l’ with char ‘c'.

public class Demo {
    public static void main(String[] args) {
        String strOld = "Hello world";
        System.out.println("Original string : " + strOld);
        String strNew = strOld.replace('l','c');
        System.out.println("Replaced string : " + strNew);
    }
}

You can run your code online here

2. replace(String oldString, String newString)

In this example we have replaced all the occurrence of String "lo" with String "ping".

public class Demo {
    public static void main(String[] args) {
        String strOld = "Hello world";
        System.out.println("Original string : " + strOld);
        String strNew = strOld.replace("lo","ping");
        System.out.println("Replaced string : " + strNew);
    }
}

You can run your code online here

3. replace(String emptyString, String newString)

In this example we have replaced all the occurrence of String "" (empty String) with String "A".

public class Demo {
    public static void main(String[] args) {
        String strOld = "Hello world";
        System.out.println("Original string : " + strOld);
        String strNew = strOld.replace("", "A");
        System.out.println("Replaced string : " + strNew);
    }
}

You can run your code online here

4. replace(String whitespace, String newString)

public class Demo {
    public static void main(String[] args) {
        String strOld = "Hello world";
        System.out.println("Original string : " + strOld);
        String strNew = strOld.replace(" ", "WHITESPACE");
        System.out.println("Replaced string : " + strNew);
    }
}

You can run your code online here

5. replaceFirst(String oldString, String newString)

public class Demo {
    public static void main(String[] args) {
        String strOld = "Hello world";
        System.out.println("Original string : " + strOld);
        String strNew = strOld.replaceFirst("l", "c");
        System.out.println("Replaced string : " + strNew);
    }
}

You can run your code online here

6. replaceAll(String regex, String newString)

public class Demo {
    public static void main(String[] args) {
        String strOld = "Hello world";
        System.out.println("Original string : " + strOld);
        String strNew = strOld.replaceFirst("\\s", "");
        System.out.println("Replaced string : " + strNew);
    }
}

You can run your code online here

Okay so that's enough for now.

Thank you for reading.

Please share your thoughts about it and correct me if I'm wrong.

I hope you liked it and found it helpful.

Cover:- Rajat Gour

Connect with me on Twitter or LinkedIn

My personal blog blog.ritvikdubey.com

split() Method

Ritvik Dubey — Sun, 22 Aug 2021 16:12:12 +0000

Hello all😀 I hope you are doing well. This is going to be a very short and very useful article. In this article I'll be writing about split() method in Java. This is a one of the most useful methods.

Let's begin...

split()

This is a method of Java String class. This method splits a given string around matches of the given regular expression. This method allows you to break a string based on specific Java string delimiter. More precisely this method splits string against given regular expression and returns a char array.

May be a few of you might have heard the word Delimiter for the first time, so, delimiter is one or more characters that separate text strings. Some very common delimiters are comma(,), semicolon (;), quotes ( ", ' ), braces ({}), pipes (|), or slashes ( / \ ).

General Syntax :-

string_name.split("delimter");

This 👆 is the general form in which you can use split() method. Let's see an example to make it clear.

public class Demo {
    public static void main(String[] args)
    {
        String str = "Hello, I'm a string";
        String[] arrOfStr = str.split(",");
        for (String a : arrOfStr) {
            System.out.println(a);
        }
    }
}

You can run your code online here

Here in this example you can see we the split string at delimiter that is at the comma.

There are two ways to split string :-

1. split(String regex)

This method takes a regular expression as a parameter and breaks the given string around matches of this regular expression regex. By default limit is 0. It returns an array of strings calculated by splitting the given string. Above example is also a type of this but we will see a more advanced example-

public class Demo {
    public static void main(String[] args)
    {
        String str = "Hello|I'm|your;String|exa#mple";
        String[] arrOfStr = str.split("[|;#]");
        for (String a : arrOfStr) {
            System.out.println(a);
        }
    }
}

You can run your code online here

Note that this takes a regular expression, so remember to escape special characters if necessary

2. split(String regex, int length)

Parameters for this are: regex (the delimiting regular expression) and limit (controls the number of times the pattern is applied and therefore affects the length of the resulting array). This returns the array of strings counted by splitting this string around matches of the given regular expression.

public class Demo {
    public static void main(String[] args) {
        String str = "8989-01214-1521654-544744";
        String[] arrOfStr = str.split("-", 2);
        for (String a : arrOfStr ) {
            System.out.println(a);
        }
    }
}

You can run your code online here

The PatternSyntaxException will be thrown if the provided regex's syntax is invalid.

Okay so that's enough for now there is lot more to learn about splitting, this article was to give you basic idea how split works.

Thank you for reading.

Please share your thoughts about it and correct me if I'm wrong.

I hope you liked it and found it helpful.

Cover:- Rajat Gour

Connect with me on Twitter or LinkedIn

My personal blog blog.ritvikdubey.com

Java contains() method

Ritvik Dubey — Sun, 15 Aug 2021 08:05:47 +0000

Hello all😀 I hope you are doing well. This is going to be a very short and very useful article. In this article I'll be writing about contains() method in Java. This method is very useful while you are doing competitive programming.

Let's begin...

contains()

This is a method of Java String class. This method returns a boolean value. This method checks if the specified substring is present in the given string. If substring is their then it returns true else it returns false. This method searches the sequence of characters in the given string. Remember this method is case-sensitive.

Syntax :-

stringVariableName.contains(substring);

Example :-

public class Demo {
    public static void main(String[] args){
        String str = "Hey, I'm the main string here!";
        System.out.println(str.contains("main string"));
    }
}

You can run your code online here

Remember it searches for the sequence of characters in the given string. This will be more clear from this example :-

public class Demo {
    public static void main(String[] args){
        String str = "Hey, I'm the main string here!";
        System.out.println(str.contains("Hey string"));
    }
}

You can run your code online here

This example will return true, we will pass an empty string in contains method but still it will return true because empty is a subset of any string.

public class Demo {
    public static void main(String[] args){
        String str = "Hey, I'm the main string here!";
        System.out.println(str.contains(""));
    }
}

You can run your code online here

If we pass null in the contains() it will throw a NullPointerException

public class Demo {
    public static void main(String[] args){
        String str = "Hey, I'm the main string here!";
        System.out.println(str.contains(null));
    }
}

You can run your code online here

There is one more way how you can use contains(), by passing string variable instead of passing a string itself.

public class Demo {
    public static void main(String[] args){
        String str = "Hey, I'm the main string here!";
        String subStr = "I'm the main";
        System.out.println(str.contains(subStr));
    }
}

You can run your code online here

We know that contains() method is case-sensitive, however there is a way you can check for the substring in the given string, using toUpperCase() or using toLowerCase() methods since both these methods and contains() method are the methods of same Java String class

public class Demo {
    public static void main(String[] args){
        String str = "Hey, I'm the main STRING here!";
        System.out.println(str.toLowerCase().contains("the main string"));
    }
}

You can run your code online here

Since contains() method returns boolean value we can use it with if else conditional statements

import java.util.Scanner;

public class Demo {
    public static void main(String[] args){
        String str = "Team Leader :- Ritvik Dubey";
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter team leader name");
        String subStr = sc.nextLine();
        sc.close();
        if(str.contains("Ritvik Dubey")) {
            System.out.println("Yes, team leader confirmed");
        }
        else {
            System.out.println("Team leader not confirmed");
        }
    }
}

You can run your code online here

Okay so that's enough for now follow my this journey to learn more about Java.

Thank you for reading.

Please share your thoughts about it and correct me if I'm wrong.

I hope you liked it and found it helpful.

Cover:- Rajat Gour

Connect with me on Twitter or LinkedIn

My personal blog blog.ritvikdubey.com

substring() Method

Ritvik Dubey — Sun, 08 Aug 2021 10:20:55 +0000

Hello All👋 I hope you all are doing well. I have published a few articles related to String in java, you can check them here. Lately I realized that I never wrote about substring. So, this is a short article about substring in Java.

Let's begin...

First, what is a String?

String is a collection of characters in sequence. In programming it is used to represent text rather than numbers. Numbers can also be considered as a string if they are specified correctly. To represent a string we enclose it in within quotes. To read more about string click here.

What is a substring?

So now we know what is a String let's learn about substring, in very short substring is a part of String or substring is a continuous sequence of characters in a string. It is a built-in method of Java String class. This method returns some part of the given String. Thus the return type of this method in Java is a String.

For example :-

Let's take a String -

"I love DEV community"

Now there can be many substrings here, few of them are -

"love" , "DEV community", "unity", "i" etc.

So a part of the given string is called substring, even a single character from the string can be printed using substring().

Let's look at some code

public class Demo {
    public static void main(String[] args) {
        String str = "I love DEV community";
        System.out.println("Original string is : " + str);
        String subStr = "";
        subStr = str.substring(7);
        System.out.println("Substring is : " + subStr);
    }
}

You can run your code online here

For your better understanding in above example I have written a little lengthy code.

Same code could be cut short to this, you don't need to declare a variable for substring always -

public class Demo {
    public static void main(String[] args) {
        String str = "I love DEV community";
        System.out.println("Original string is : " + str);
        System.out.println("Substring is : " + str.substring(7));
    }
}

You can run your code online here

And the output will be same -

Let's look at the two variants of substring()

1. substring(int startingIndex);

The above example is actually the example of this variant, in this variant we specify the starting index from which index we want to make a substring. This variant returns the substring that starts at the given index and then runs through the entire original String.

Let's look at a different example.

public class Demo {
    public static void main(String[] args) {
        String str = "Java is my favorite programming language";
        System.out.println("Original string is : " + str);
        System.out.println("Substring is : " + str.substring(7));
    }
}

You can run your code online here

2. substring(int startingIndex, int endingIndex);

In this variant we will take two inputs, first, starting index, this is the value of beginning index, inclusive and second the ending index, this is the value of ending index, exclusive, meaning the substring ends at the ending index – 1 index.

Let's look at its example.

public class Demo {
    public static void main(String[] args) {
        String str = "I love coding";
        System.out.println("Original string is : " + str);
        System.out.println("Substring is : " + str.substring(2, 6));
    }
}

You can run your code online here

Remember the index starts from 0.

There can be a exception thrown, IndexOutOfBoundException, if the value of starting index is greater than the length of the entire String or less than 0 or if starting index is greater than ending index and if the ending index is greater than the length of String.

Printing a single character using substring()

public class Demo {
    public static void main(String[] args) {
        String str = "I love coding";
        System.out.println("Original string is : " + str);
        System.out.println("Substring is : " + str.substring(4, 5));
    }
}

You can run your code online here

Printing a null string using substring()

public class Demo {
    public static void main(String[] args) {
        String str = "I love coding";
        System.out.println("Original string is : " + str);
        System.out.println("Substring is : " + str.substring(0, 0));
    }
}

You can run your code online here

This is not necessary if you pass starting index and ending index as 0 to print a null string, if there is 0 difference between both the index then also the output will be null.

public class Demo {
    public static void main(String[] args) {
        String str = "I love coding";
        System.out.println("Original string is : " + str);
        System.out.println("Substring is : " + str.substring(2, 2));
    }
}

You can run your code online here

Output is same in both the cases.

Okay so that's enough for now follow my this journey to learn more about Java.

Thank you for reading.

Please share your thoughts about it and correct me if I'm wrong.

I hope you liked it and found it helpful.

Cover:- Rajat Gour

Connect with me on Twitter or LinkedIn

My personal blog blog.ritvikdubey.com

printf() in Java

Ritvik Dubey — Sun, 01 Aug 2021 15:25:11 +0000

Hello People👋 I hope you are doing well. Yes so you have read the title of the article, printf() in Java, I have recently came across this method, I did some research about this and thought to write about it. So this is gonna be interesting as well as useful for competitive programming. This is actually a part of formatting in java.

Let's begin...

What is formatting

You all know there are two methods println and print to print standard output, but in java.io package there is this class PrintStream which has two formatting methods format and printf, these both methods can be used to replace print and println methods. Both these methods, fromat and printf are equivalent to one another. Both of these methods gives you more control over your print output when numbers are included in your output, soon you'll understand it better. In this article we will talk about printf only.

System.out.printf()

So now you already know this method is part of the java.io.PrintStream class, this method provides String formatting similar to the printf() function in C language. It is also an overloaded method of the PrintStream class. The method returns the output stream and it accepts up to three parameters depending on the overloading.

Let's first look at its syntax:-

System.out.printf(string); (the string parameter is simple as the printIn() method)

System.out.printf(format, arguments);

System.out.printf(locale, format, arguments);

Format

To specify the formatting rules we use the format parameter. This string is composed of literals and format specifiers. Rules start with the % character. Arguments are required only if there are format specifiers in the format string. Format specifiers include flags, width, precision, and conversion characters in the below sequence:-

%[flags][width][.precision]conversion-character

Specifiers in the brackets are optional.

Conversion Characters

d : formats decimal integer [byte, short, int, long]
f : formats floating-point number [float, double]
c : formats character Capital C will uppercase the letter
s : formats String Capital S will uppercase all the letters in the string
n : adds a new line character
t : formats date/time values.

There are many other conversion characters, we will see few more in examples

Flags

The [flags] define standard ways to modify the output.

- : left-justify ( default is to right-justify )
+ : output a plus ( + ) or minus ( - ) sign for a numerical value
0 : forces numerical values to be zero-padded ( default is blank padding )
** (space)** : display a minus sign if the number is negative or a space if it is positive.

Width

The [width] specifies the field width for outputting the argument. It represents the minimum number of characters to be written to the output.

Precision

The [.precision] specifies the number of digits of precision or the length of a substring to extract from a String. Numbers are rounded to the specified precision.

Examples

String Formatting

System.out.printf("%s", "Hello");

public class Demo {
   public static void main(String[] args) {
      System.out.printf("%s", "Hello");
   }
}

You can run your code online here

This one will change String into uppercase

System.out.printf("%S", "Hello");

public class Demo {
   public static void main(String[] args) {
      System.out.printf("%S", "Hello");
   }
}

You can run your code online here

*In this example I have used - flag *

public class Demo {
   public static void main(String[] args) {
      System.out.printf("'%-10s'", "Hello");
   }
}

You can run your code online here

Character Formatting

System.out.printf("%c", "e");

public class Demo {
   public static void main(String[] args) {
      System.out.printf("%c", 'e');
   }
}

You can run your code online here

This one will change character into uppercase

System.out.printf("%C", "e");

public class Demo {
   public static void main(String[] args) {
      System.out.printf("%C", 'e');
   }
}

You can run your code online here

Number Formatting

System.out.printf("%d", 10005);

public class Demo {
   public static void main(String[] args) {
      System.out.printf("%d", 10005);
   }
}

You can run your code online here

In this example we will use locale for a thousand separator

System.out.printf(Locale.US, "%,d %n", 100500);

import java.util.Locale;

public class Demo {
   public static void main(String[] args) {
      System.out.printf(Locale.US, "%,d %n", 100500);
   }
}

You can run your code online here

System.out.printf("%f", 55.1458);

public class Demo {
   public static void main(String[] args) {
      System.out.printf("%f", 55.1458);
   }
}

You can run your code online here

In this example we will reduce the length of decimal part

System.out.printf("%.3f", 55.1458);

public class Demo {
   public static void main(String[] args) {
      System.out.printf("%.3f", 55.1458);
   }
}

You can run your code online here

Date and Time Formatting

System.out.printf("%tT", date);

import java.util.Date;

public class Demo {
   public static void main(String[] args) {
      Date date = new Date();
      System.out.printf("%tT", date);
   }
}

You can run your code online here

In this example we will print Hours, Minutes and Seconds separately

System.out.printf("hours %tH: minutes %tM: seconds %tS%n", date, date, date);

import java.util.Date;

public class Demo {
   public static void main(String[] args) {
      Date date = new Date();
      System.out.printf("hours %tH: minutes %tM: seconds %tS%n", date, date, date);
   }
}

You can run your code online here

In this example we will print full day of the week using A, full month name using B and year in four digits using Y.

System.out.printf("%1$tA, %1$tB %1$tY %n", date);

import java.util.Date;

public class Demo {
   public static void main(String[] args) {
      Date date = new Date();
      System.out.printf("%1$tA, %1$tB %1$tY", date);
   }
}

You can run your code online here

Boolean Formatting

System.out.printf("%b", 5<4);

public class Demo {
   public static void main(String[] args) {
      System.out.printf("%b", 5<4);
   }
}

You can run your code online here

In this example we will print output in uppercase

System.out.printf("%B", 5<4);

public class Demo {
   public static void main(String[] args) {
      System.out.printf("%B", 5<4);
   }
}

You can run your code online here

New Line

System.out.printf("This%nline%nwill%nbreak");

public class Demo {
   public static void main(String[] args) {
      System.out.printf("This%nline%nwill%nbreak");
   }
}

You can run your code online here

Here is the problem where I found printf() very useful -

In each line of output there should be two columns:
The first column contains the String and is left justified using exactly 15 characters.
The second column contains the integer, expressed in exactly 3 digits; if the original input has less than three digits, you must pad your output's leading digits with zeroes.

Solution using printf()

import java.util.Scanner;

public class Demo {
    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        System.out.println("================================");
        for(int i=0;i<3;i++)
        {
            String s1=sc.next();
            int x=sc.nextInt();
            System.out.printf("%-15s%03d%n", s1, x); //
        }
        System.out.println("================================");
    }
}

You can run your code online here

Solution without using printf()

import java.util.Scanner;

public class Demo {
   public static void main(String[] args) {
      Scanner sc=new Scanner(System.in);
      System.out.println("================================");
      for(int i=0;i<3;i++){
         String s1=sc.next();
         int x = sc.nextInt();
         String newX = "";
         if(x>=0 && x<=9) {
            newX = "00";
         }
         else if(x>=10 && x<=99) {
            newX = "0";
         }
         else {
            newX = "";
         }
         int ct = s1.length();
         int space = 15 - ct;
         String bspc = "";
         for(int j=0; j<=space-1; j++) {
            bspc = bspc +" ";
         }
         System.out.println(s1 + bspc + newX+x);
      }
      System.out.println("================================");
   }
}

You can run your code online here

Here are few more formattings

Resources-

Video ||
pdf

Okay so that's enough for now follow my this journey to learn more about Java.

Thank you for reading.

Please share your thoughts about it and correct me if I'm wrong.

I hope you liked it and found it helpful.

Cover:- Rajat Gour

Connect with me on Twitter or LinkedIn

My personal blog blog.ritvikdubey.com

Comparing Strings

Ritvik Dubey — Sun, 25 Jul 2021 10:12:02 +0000

Hello all😀 I hope you are doing well. In this article I'll be writing about 4 ways to compare strings in Java. Before continuing this article I would suggest you to go through my last 2 articles, String class and String Methods, if you haven't been through them please check these two short reads.

Let's begin...

Before continuing let's understand why we need to compare Strings, if you want to check some character values or if you are making a simple application where there is login or pin feature you might need to compare strings there. So here are such 4 methods which will be of use while working with String.

1. == operator

Yes the first way to compare Strings is double equal to or equal to equal to (==) relational or comparison operator. This operator is used for checking if the value of two operands is the equal or not. This operator is used to compare two or more than two objects, if they are referring to the same object then it returns true. This operator compares objects references. In short we can say this operator checks values.

public class Demo {
    public static void main(String []args) {
        String str1 = "Lion";
        String str2 = "Lion";
        if(str1 == str2) {
            System.out.println("Same");
        }
        else {
            System.out.println("Not same"); 
        }
    }
}

You can run your code online here

2. equals()

I have already written about this method in my last article, this method returns true if and only if the object is a string and represents the same sequence of characters as this string. Returns true if the current object is the equal as the argument and returns false if objects are not equal. In short this method checks values of both the strings. This time let's understand this with some different example.

public class Demo {
    public static void main(String []args) {
        String str1 = "Lion";
        String str2 = "Lion";
        if(str1.equals(str2)) {
            System.out.println("Same");
        }
        else {
            System.out.println("Not Same");
        }
    }
}

You can run your code online here

3. equalsIgnoreCase()

This method works same as equals() method do, but this method ignores case of the string, it returns true even if the case of string is not same., which means equalsIgnoreCase() method is case insensitive in nature.

public class Demo {
    public static void main(String []args) {
        String str1 = "Lion";
        String str2 = "LiOn";
        if(str1.equalsIgnoreCase(str2)) {
            System.out.println("Same");
        }
        else {
            System.out.println("Not Same");
        }
    }
}

You can run your code online here

If same code is executed with equals() method the output will be "Not same".

public class Demo {
    public static void main(String []args) {
        String str1 = "Lion";
        String str2 = "LiOn";
        if(str1.equals(str2)) {
            System.out.println("Same");
        }
        else {
            System.out.println("Not Same");
        }
    }
}

You can run your code online here

4. compareTo()

This method compares strings on the basis of the Unicode value of each character in the strings. This method returns an integer values, these values may be less than, equal, or greater than zero. If two strings are different, they have different characters at same index, or their lengths are different, or both. In short we can say this method checks difference of Unicode values.

Let's understand this better with a few examples-

public class Demo {
    public static void main(String []args) {
        String str1 = "K";
        String str2 = "K";
        System.out.println("The difference is : " + str1.compareTo(str2));
    }
}

You can run your code online here

In the above example we compared two similar characters, character K whose Unicode value is 75. Hence the value which got printed is 0, i.e., there is no difference between Unicode values.

public class Demo {
    public static void main(String []args) {
        String str1 = "K";
        String str2 = "k";
        System.out.println("The difference is : " + str1.compareTo(str2));
    }
}

You can run your code online here

In the above example we compared two different cases of character K, that is we compared K and k whose Unicode values are 75 and 107. Hence the value which got printed is -32, i.e., difference between Unicode values of K and k.

public class Demo {
    public static void main(String []args) {
        String str1 = "k";
        String str2 = "K";
        System.out.println("The difference is : " + str1.compareTo(str2));
    }
}

You can run your code online here

In the above example we compared two different cases of character K, that is we compared K and k whose Unicode values are 75 and 107 but this time we changed the order. Hence the value which got printed is 32, i.e., difference between Unicode values of k and K.

public class Demo {
    public static void main(String []args) {
        String str1 = "AB";
        String str2 = "Ab";
        System.out.println("The difference is : " + str1.compareTo(str2));
    }
}

You can run your code online here

In the above example we compared two different strings, AB and Ab in which first character of both the strings are same but there is difference of case in second character. Hence the value which got printed is -32, i.e., difference between Unicode values of B and b and the difference between Unicode values of first character A is same so it didn't affected the final result.

public class Demo {
    public static void main(String []args) {
        String str1 = "Hello";
        String str2 = "Hi";
        System.out.println("The difference is : " + str1.compareTo(str2));
    }
}

You can run your code online here

In the above example we compared two different strings, Hello and Hi in which first character of both the strings are same but second character of both the Strings is different, i.e., e and i whose Unicode values are 101 and 105 respectively. Hence the value which got printed is -4, i.e., difference between Unicode values of e and i and the difference between Unicode values of first character H is same so it didn't affected the final result.

For reference you can check Unicode values here

Okay so that's enough for now follow my this journey to learn more about Java.

Thank you for reading.

Please share your thoughts about it and correct me if I'm wrong.

I hope you liked it and found it helpful.

Cover:- Rajat Gour

Connect with me on Twitter or LinkedIn

My personal blog blog.ritvikdubey.com

String Methods

Ritvik Dubey — Sun, 18 Jul 2021 18:21:12 +0000

Hello all😀 I hope you are doing well. In this article I'll be writing about some most commonly used methods of string class in java. May be I'll write one more article about the methods. In this article I'll go in some depth to make it easy to understand how to use String class methods. If you haven't read my last article then please go through that short read first it about String class.

Let's begin...

1. length()

This method returns the length of a specified string. This method returns count of total number of characters. This method returns integer value. This method is most commonly used while you are working on loops.

public class Test {
    public static void main(String []args)
    {
        String str = "This is a test string";
        System.out.println("The length of the String is :  " + str.length());
    }
}

You can run your code online here

There is this one length method also there in java. This method is used to find out the length of an array in java.

public class DemoArray {
    public static void main(String []args)
    {
        int[] arr = new int[69];
        System.out.println("The length of the array is : " + arr.length);
    }
}

You can run your code online here

2. isEmpty()

This method checks if a given string is empty or not. This method returns True if the string is empty which means if the length of the given string is 0. This method returns boolean value.

public class Demo {  
    public static void main(String []args) {  
        String str1="";  
        String str2="This is a test string";  
        System.out.println("This is for str1 : " + str1.isEmpty());  
        System.out.println("This is for str2 : " + str2.isEmpty());  
    }
}

You can run your code online here

There is this method isBlank(), this method is similar to isEmpty() but additionally checks for whitespace in the given String. This method was introduced in Java 11.

3. toUpperCase()

This method returns the UPPERCASE from of a specified string. This method converts all of the characters in this String to upper case. Since Java is a case-sensitive programming language this method have its own importance. This method is mostly used when dealing with validations.

public class Demo {
    public static void main(String []args) {
        String str = "this complete string was in lower case";
        String subStr = str.toUpperCase();
        System.out.println(subStr);
    }
}

You can run your code online here

There is this method toLowerCase() which is used to convert the given string into lower-case.

public class Demo {
    public static void main(String []args) {
        String str = "THIS COMPLETE STRING WAS IN UPPER CASE";
        String subStr = str.toLowerCase();
        System.out.println(subStr);
    }
}

You can run your code online here

4. equals()

This method returns true if and only if the object is a string and represents the same sequence of characters as this string. Returns true if the current object is the equal as the argument and returns false if objects are not equal.

public class Demo {
    public static void main(String []args) {
        String str = "First string";
        System.out.println(str.equals("First string"));
    }
}

You can run your code online here

There are several other methods to compare in Java, I'll write about those in a separate article.

5. charAt()

This method returns the character at the given index in the specified string. The indexing starts from 0 here, i.e., the first letter is at 0 index. This method returns a char value.

public class Demo {
    public static void main(String []args) {
        String str = "To find index of character at 15th index in the string";
    char result = str.charAt(15);
        System.out.println("Character at 15th index is : " + result);
    }
}

You can run your code online here

Okay so that's enough for now follow my this journey to learn more about Java.

Thank you for reading.

Please share your thoughts about it and correct me if I'm wrong.

I hope you liked it and found it helpful.

Cover:- Rajat Gour

Connect with me on Twitter or LinkedIn

My personal blog blog.ritvikdubey.com

String class in Java

Ritvik Dubey — Sun, 11 Jul 2021 09:43:49 +0000

Hello People😀 I hope you all are doing well. This short article will be introduction about String class in java.

Let's begin...

What is a String?

phrase = Hello

This is not considered as a string.

phrase = "Hello"

Since it is enclosed by quotes here this is a string.

number = 1234

This is not considered as a string, this is considered as a number or to be more precise in programming this is considered as integer vale or int. All arithmetic operations can be performed on it.

number = "1234"

Since it is enclosed by quotes so here this will be considered as a string.

Remember we are talking about Java so please do not forget :-

So in Java all those examples will look like:-

phrase = "Hello";
//and
number = "1234";

What is a String class?

In Java String is a class found in the java.lang package. String is a class and not a data type like int and char. The String class represents character strings. In Java Strings are treated as objects and all string objects in Java are the instance of this String class. Strings are immutable, once it is created a String object can not be changed. The String objects are backed internally by a char array it means an array of character in Java works same as a Java String.

This will be more clear from the example:-

char[] ch = {'H','e','l','l','o'};  
String st = new String(ch);

This works same as:-

String st = "Hello";

How String is created?

There are two ways String is created:-

1. Using literal syntax

Create a variable of type String and directly assign it a value in quotes:-

String phrase = "Hello People";

Complete Code:-

public class StringDemo {
    public static void main(String []args) {
        String phrase = "Hello People";
        System.out.println(phrase);
    }
}

You can run your code online here

Output:-

2. Using new keyword syntax

Create a new String object and add the literal in quotes.

String phrase = new String("Hello People");

Complete Code:-

public class StringDemo {
    public static void main(String []args) {
        String phrase = new String("This one using new keyword");
        System.out.println(phrase);
    }
}

You can run your code online here

Output:-

There are many String methods which can be used to find length of string or to add two strings or to split a string or to change it's case etc, in next article we will talk about some most used String methods. Also there's lot left to explore about String but I wanted to keep it and introductory article, so ending it here.

Okay so that's enough for now follow my this journey to learn more about Java.

Thank you for reading.

Please share your thoughts about it and correct me if I'm wrong.

I hope you liked it and found it helpful.

Cover:- Rajat Gour

Connect with me on Twitter or LinkedIn

My personal blog blog.ritvikdubey.com

Shut Down with Runtime class

Ritvik Dubey — Sun, 04 Jul 2021 17:21:53 +0000

Hello All👋 I hope you all are doing well. In this very short article I'll be writing about how you can shut down your system using Runtime class in Java.

Let's begin...

What is Runtime class?

Java Runtime class is used to interact with java runtime environment. Java Runtime class provides methods to execute a process, invoke GC, get total and free memory etc. There is only one instance of java.lang.Runtime class is available for one java application.

Let's not get much into Runtime class and see how to shut down your pc.

For doing so we must know a few things first:-

getRuntime() method

This method returns the runtime object associated with the current Java application. This is a static method of Runtime class, to know more about static method read my last article static keyword in Java, since this is a static method we will call this method without creating an object of the class.

Runtime.getRuntime();

exec() method

To execute a system command we pass the command string to the exec() method of the Runtime class. The exec() method returns a Process object that abstracts a separate process executing the command. From the Process object we can get outputs from and send inputs to the command. To use this method we will call it using method().method() syntax since both the methods are of same class.

Runtime.getRuntime().exec();

Let's see code to shutdown your pc

To shut down we will use the command shutdown -s. We can also specify the time after which you want to make your computer shut down.

import java.lang.Runtime;
import java.util.Scanner;

public class ShutDown {
    public static void main(String[] args)throws Exception {
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter Password");
        String pass = sc.next();
        if(pass.equals("xyz")) {
            System.out.println("Welcome, you entered correct password");
        }
        else {
            System.out.println("You entered wrong password, soon your machine will shut down automaticallly");
            run.exec("shutdown -s");
        }
    }
}

On compiling above code

On entering correct password

On entering incorrect password

Several other tasks you can perform instead of shut down

On replacing line number 14 with below code you can shut down your pc after specified time

run.exec("shutdown -s -t");

On replacing line number 14 with below code you can restart your pc

run.exec("shutdown -r");

On replacing line number 14 with below code you can restart your pc after specified time

run.exec("shutdown -r -t");

On replacing line number 14 with below code you can log out of your pc

run.exec("shutdown -l");

On replacing line number 14 with below code you can log out of your pc after specified time

run.exec("shutdown -l -t");

On replacing line number 14 with below code you can lock your pc

run.exec("c:/windows/system32/rundll32.exe user32.dll, LockWorkStation");

Apart from this you can run system applications(.exe) using it

import java.io.IOException;

public class SystemApp {
    public static void main(String[] args) {
        try {
            Runtime run = Runtime.getRuntime();
            String path = "C:\\Users\\hp\\AppData\\Local\\Programs\\Microsoft VS Code\\Code.exe";
            Process process = run.exec(path);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}