How to take input in Java?

Java provides java.lang package and System class to take input from users and display output on an output device.

                               java.lang   (package)

                                                          Object     (Super Class)

                                                                     System      (Sub Class)
PrintStream(It is used to manage output operation)          InputStream(It is used to manage input operation)
print()                                                                                    read()
println()
PrintStream out;
out is the reference variable of PrintStream class which is used to access print() or println()

System.out.print()       // display output without new line char \n

System.out.println();  // display output with new line char  \n 
InputStream in;
"in" is the reference of InputStream class which will be used to call read() for input operation
System.in.read();
but read() return byte data and throw exception IOException hence System.in reference will be managed by the Scanner class which will store input data in an Object pattern.
Scanner sc = new Scanner(System.in);

note:-  Scanner is not used to take input, it will only manage input data of System.in reference hence Scanner is also called Input Manager Class.

Scanner class provides a predefined method to convert object type to another data type of Java.

int a = sc.nextInt()  //Scanner object data to integer
float b = sc.nextFloat()  //float
double d = sc.nextDouble()  //double
String s = sc.next();   //string
String s1 = sc.nextLine();  //paragraph
Example of System.in.read()?
import java.io.*;
class InputDemo
{
   public static void main(String args[]) throws IOException
   {
       int a = System.in.read();
       System.out.println((char)a);

    }
}

...................................................................................

Scanner class Example to manage integer and char input operation:-

import java.util.*;

class InputDemo

{

    public static void main(String scs[])

    {

        Scanner st = new Scanner(System.in);

        System.out.println("Enter int");

        int a1 =st.nextInt();

        System.out.println(a1);

        System.out.println("Enter char");

        char a2 =st.next().charAt(0);

        System.out.println(a2);

    }

}

Another Example of Scanner Class in Java:-

import java.util.Scanner;

class InputDemo
{
   public static void main(String args[])
   {
            Scanner sc = new Scanner(System.in);   // System.in is mandatory to pass under Scanner Objectg
       System.out.println("enter first number");
       int a = sc.nextInt();
       System.out.println("enter second number");
       int b = sc.nextInt();
       System.out.println(a+b);
    }
}
Scanner class Example with all datatype:-

import java.util.Scanner;

class AllInput

{

   public static void main(String args[])

   {

          int a;

          char ch;

          String s;

          float f;

          double d;

          Object o;

          Integer i;

          Float f1;

          Scanner sc = new Scanner(System.in);

          System.out.println("enter int, char, string, float, double, object, 

Integer, Float ");

         a = sc.nextInt();

         ch = sc.next().charAt(0);

         s = sc.next();

         f = sc.nextFloat();

         d = sc.nextDouble();

         o = sc.next();

         i = sc.nextInt();

         f1 = sc.nextFloat();

         System.out.println("a = "+a + "ch = "+ch + "s = "+s + "f = "+f + "d="+d+" 

o="+o+" i="+i + "f="+f1);

           }

}

......................................................................................................................................................................

Using Command Prompt:-

The command prompt is a very old approach to take input from users, this is used on command-line interface-based software.

DOS is the best example of command-line input,  we can manage all DOS operations using a set of commands.

The database also works using a terminal that is the command-based software system.

Java provides a parametrized String array under main() to handle command-line input.

Java can not create multiple types of main() hence it has created a single main() to perform all tasks.

public static void main(String args[])   //here args[] is the string array

{

}

 Create program:-

class InputExample2

{

   public static void main(String args[])

   {

        String s = args[0];

        String s1 = args[1];

        System.out.println("value is "+s + " value is "+s1);

   }

}

Compile

javac InputExample2.java

java InputExample2 "hello" "12.345"

Program of addition using Command Prompt Input

class InputExample2

{

   public static void main(String args[])

   {

        int s = Integer.parseInt(args[0]);

        int s1 =Integer.parseInt(args[1]);

        System.out.println(s+s1);

   }

}

Another Example of Command-Line input in java:-

class CommandInput

{

   public static void main(String args[])

   {

       // System.out.println(args[0] + "," + args[1] + " ," + args[2]);

        for(String s:args)

        {

            System.out.println(s);

        }   

    }

}

java provides the Wrapper class to convert the primitive data type to object type.

Integer, Float, Double, Character, Boolean is the Wrapper class of Java.

parseInt() method to convert Object to Integer  or String to integer using Integer.parseInt()

parseFloat() method to convert Object to float or String to float using Float.parseFloat().

Assignments of Command-Line Input In Java?

1)  WAP to calculate simple interest using Command Line Input?

2)  WAP to calculate the area of Triangle using Command Line Input?

3) WAP to calculate Area of Circle using Command Line Input?

4)  WAP to calculate the Swap program using Command Line Input?

5)  WAP to calculate Square and Cube using Command Line Input?

How to take input from user's in Stream Class:-

import java.io.*;

class StreamInput

{

   public static void main(String args[]) throws IOException

   {       

       InputStreamReader ir = new InputStreamReader(System.in);

       BufferedReader br = new BufferedReader(ir);

       String s = br.readLine();

       System.out.println(s); 

   }

}