Chapter 7 What is Constant and How to get User Input in java Explain in Details

 Constant and User Input 

What is Constant in Java ?

• An element of program whose value can not be changed ( Static type) at the time of execution of program is called constant.
• It is also called literals.
• It may be int,float and character data type.

Note:- Guys Next Chapter discuss on Data Types Topics in Easy Way- Chapter 8

Rules for Constructing Integer Constant 

• It must have atleast one digit.
• It must not have a decimal point.
• It may be positive or negative.
• No comma or blank space are allowed in integer constant.

Rules for Constructing Floating Point Constant 

• It must have atleast one digit.
• It must have a decimal point.
• It may be positive or negative.
• No comma or blank space are allowed in floating point constant.

Rules for constructing Character constant

• It is a single alphabet,digit or special symbol.
• The length of character constant is 1 character.
• Character constant is enclosed within single quotes (Example char c='A';).

User input in Java 

1. Import Scanner in java:

• 1.Scanner is a predefined class which is used to take user input in java.
• 2.Scanner class is defined inside java.util package.
• 3.Scanner class consists of many function to take user input which is given below.

Some Important Point: 

• nextInt():Used to read integer value from the user.
• nextFloat():Used to read float value from the user.
• nextDouble():Used to read double value from the user.
• next():Used to read string value without space from the user.
• nextLine():Used to read string value from the user.
• nextByte():Used to read byte value from the user.
• nextShort():Used to read short value from the user.
• nextLong():Used to read long value from the user.

Example 1 : User Input in Java

• import java.util.Scanner; // Import the pakage for java

//Q1 Print Student Details

import java.util.Scanner;

class Stud{  

  public static void main(String[] args) {  

    String name;

    int rollno;

    float marks;

    //instance of class Scanner

    Scanner obj= new Scanner(System.in);  

// // Get the value by user

    System.out.println("Enter your name");

    name = obj.nextLine();  //taking string input

    System.out.println("Enter your rollno");

    rollno = obj.nextInt();//taking integer input

    System.out.println("Enter your marks");

    marks = obj.nextFloat();//taking float input

//printing the output

    System.out.println("Name=" + name);

    System.out.println("Rollno=" + rollno);

    System.out.println("Marks=" + marks);

  }

}

### OUETPUT###

   

    Enter your name

    Annu Priya

    Enter your rollno

    82006

    Enter your marks

    475

    Your Name=Annu Priya

    Your Roll Number=82006

    Your Marks=475.0

Q2. Addition two Number :  

import java.util.Scanner; //import the java pakage

class Addd{  

  public static void main(String[] args) {  

// Add of Two Number

Scanner sc= new Scanner(System.in);  

        System.out.println("Enter 1st Number:- ");

        int a= sc.nextInt();

        System.out.println("Enter 2nd Number:- ");

        int b= sc.nextInt();

        int c= a+b;

        System.out.println("Total Value: " +c);

  }

}

### OUETPUT###

   

    Enter 1st Number:-

    45

    Enter 2nd Number:-

    65

    Total Value: 110

2.Import ReaderStream in java

• 1.BufferedReader is a predefined class which is used to take user input in java.
• 2.It is defined inside the java.io package.

• //importing the package
• 
  
• import java.io. *; // use only 
• or 
• import java.io.BufferedReader;
• import java.io.InputStreamReader;

//importing the package

import java.io.*; // you can use only for

import java.io.BufferedReader;

import java.io.InputStreamReader;

class Easy

{

 public static void main(String[] args)

 {

  //creating the instance of class BufferedReader

 BufferedReader reader=new BufferedReader

(newInputStreamReader(System.in));

  String name;

   try {

  System.out.println("Enter your name");

  name=reader.readLine();//taking string input

  System.out.println("Name="+name);

    } catch (Exception e) {

    }

 }

} //I think this very difficult face so ignore this step

### Output ###

Enter your name :Shailesh

Name: Shailesh

3.Use Command Prompt in java:

If you want using command prompt get value by user then use cmd application :

Let's See Some Example for this: 

Example 3.1: Concatenation of value 

What is  concatenation in Java?

Concatenation in the Java programming language is the operation of joining two strings together. You can join strings using either the addition (+) operator or the String's concat() method.

class Cmd{

    public static void main(String as[]){

        System.out.print(as[0]);

        System.out.print(as[1]);

        System.out.println(as[1]+ as[0]);

    }

}

### Output ###

PS F:\Learning File\BCA\BCA 3rd Sem\JAVA OOP\javaclass> java Cmd

5Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: Index 1 out of bounds for length 1

        at Cmd.main(8thDInp.java:12)

• How to solve Index 1 out of bounds.............. problem:
• Note : Which time run program using java-file name  '' java Cmd''
• But Note Show your current value then time used 
• java-file name and value according to your arrays index
• for example :-    
  
  

  java Cmd 5 8      

  5885 // Current Output
• 
  
• So follow this step solve your index bounds problem.
• Your current value show concatenation type. 

Guys if you want solve Concatenation problem, how to get my exact value then using Wrapper class :

Example 3.2: Using Wrapper class solve concat() problem.

 

// Program : Addition of Two value

class Cmd1{

    public static void main(String ar[]){

        System.out.print( Integer. parseInt(ar[0]) + Integer. parseInt(ar[1]));   //find one line

    }

}

### Output ###

java Cmd1 5 8    

13

Example 3.3 : Using Wrapper but JavaScript Type

class Cmd2{

    public static void main(String ar[]){

        int a= Integer. parseInt(ar[0]);

        int b= Integer. parseInt(ar[1]);

        int c= a+b; // Find JavaScript Methods

        System.out.println("Addition = "+c);

    }

}

### Output ###

 java Cmd2 4 9    

Addition = 13

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