Java Program to Display Odd Numbers From 1 to 100

In Java, the most popular way to read numbers from standard input is to use the Scanner class. Sometimes, we also use the class BufferedReader class to read a number. It provides different methods related to the input of different primitive types. In this section, we will learn how to create Java programs to read numbers from the user through the standard input, such as the keyboard.

We can use the following classes to read a number:

Using Scanner class
Using BufferedReader Class
Using Command-Line Arguments

Using Scanner class

The Scanner class is defined in the java.util package. So, it is mandatory to import the package while using the Scanner class. The class also provides the methods to take input of different primitive types, such as int, double, long, char, etc.

In order to read a number (integer) from the user, we first create an object of the Scanner class and then invoke the nextInt() method.

It is the most preferred method to take input of primitive types. Similarly, we can also use nextDouble(), nextLong(), nextFloat(), etc. method if we want to read double, long, and float type from standard \input.

ReadNumberExample1.java

import java.util.Scanner;
public class ReadNumberExample1
{
public static void main(String[] args) 
{
//object of the Scanner class
Scanner sc=new Scanner(System.in);
System.out.print("Enter a number: ");
//invoking nextInt() method that reads an integer input by keyboard
//storing the input number in a variable num
int num = sc.nextInt();
//closing the Scanner after use
sc.close();
//prints the number
System.out.println("The number entered by the user is: "+num);
}
}

Output:

Enter a number: 89
The number entered by the user is: 89

Using BufferedReader Class

Java BufferedReader class is used to read the text from a character-based input stream. It provides the method readLine() to read data line by line. It makes the performance fast. It inherits the Reader class. It is defined in the java.io package so, we must import the package at the starting of the program. The disadvantage to use this class is that it is difficult to remember.

To read a number, first, create a constructor of the BufferedReader class and parse a Reader as a parameter. We have parsed an object of the InputStreamReader class. After that, we have invoked the parseInt() method of the Integer class and parses the readLine() method of the BufferedReader class. The readLine() method reads a line of text.

ReadNumberExample2.java

import java.io.*;
public class ReadNumberExample2
{
public static void main(String args[]) throws IOException
{
//creating an object of InputStreamReader class
InputStreamReader read=new InputStreamReader(System.in);
//creating a constructor of the BufferedReader class
BufferedReader in=new BufferedReader(read);
System.out.print("Enter a number: ");
//reading a number from the keyboard
int number=Integer.parseInt(in.readLine());
//prints the number that we have entered
System.out.print("You have entered: "+number);
}
}

Output:

Enter a number: 23
You have entered: 23

In the above example, we can merge the following in a single line.

InputStreamReader read=new InputStreamReader(System.in);
BufferedReader in=new BufferedReader(read);

Using Command-Line Arguments

In the command line arguments, we read the number from the standard input at the execution time of the program. The arguments passed from the console can be received in the java program and it can be used as an input. When JVM receives the command line arguments, it wraps these numbers and transferred to args[].

In the following program, we have provided the number at the execution time and converted that numbers into the integer by using the Integer.parseInt() method. Because command line arguments accept only String type.

To run the program, follow the steps, given below:

Save the program with the name java
Compile the program by typing the command javac ReadNumberExample3.java
Run the program by typing the command java ReadNumberExample3 12 90

Where 12 and 90 are command-line arguments.

Note: You can provide your input.

ReadNumberExample3.java

public class ReadNumberExample3
{
public static void main(String args[])
{
int a,b,sum;
x=Integer.parseInt(args[0]);   //first input number 
y=Integer.parseInt(args[1]);  //second input number
sum=a+b; //adding two numbers
System.out.println("The sum of " + a + " and " + b +" is " +sum);
}
}

Output: