Reading Data from Keyboard in Java

There are many ways to read data from the keyboard. For example:

1. InputStreamReader
2. Console
3. Scanner
4. DataInputStream etc.

InputStreamReader class: InputStreamReader class can be used to read data from keyboard.It performs two tasks:

• connects to input stream of keyboard
• converts the byte-oriented stream into character-oriented stream

BufferedReader class:

BufferedReader class can be used to read data line by line by readLine() method.

Example of reading data from keyboard by InputStreamReader and BufferdReader class:

In this example, we are connecting the BufferedReader stream with the InputStreamReader stream for reading the line by line data from the keyboard.

import java.io.*;  

class G5{  

public static void main(String args[])throws Exception{  

  

InputStreamReader r=new InputStreamReader(System.in);  

BufferedReader br=new BufferedReader(r);  

  

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

String name=br.readLine();  

System.out.println("Welcome "+name);  

 }  

}  

Output:Enter your name

       Amit

       Welcome Amit

Another Example of reading data from keyboard by InputStreamReader and BufferdReader class until the user writes stop:

In this example, we are reading and printing the data until the user prints stop.

import java.io.*;  

class G5{  

public static void main(String args[])throws Exception{  

  

 InputStreamReader r=new InputStreamReader(System.in);  

 BufferedReader br=new BufferedReader(r);  

  

 String name="";  

  

  while(name.equals("stop")){  

   System.out.println("Enter data: ");  

   name=br.readLine();  

   System.out.println("data is: "+name);  

  }  

 br.close();  

 r.close();  

 }  

}  

Output:Enter data: Amit

       data is: Amit

       Enter data: 10

       data is: 10

       Enter data: stop

       data is: stop

Java Console class: The Java Console class is be used to get input from console. It provides methods to read text and password. If you read password using Console class, it will not be displayed to the user. The java.io.Console class is attached with system console internally. The Console class is introduced since 1.5.

Let's see a simple example to read text from console.

String text=System.console().readLine();  

System.out.println("Text is: "+text);  

Methods of Console class

Let's see the commonly used methods of Console class.

Method	Description
1) public String readLine()	is used to read a single line of text from the console.
2) public String readLine(String fmt,Object... args)	it provides a formatted prompt then reads the single line of text from the console.
3) public char[] readPassword()	is used to read password that is not being displayed on the console.
4) public char[] readPassword(String fmt,Object... args)	it provides a formatted prompt then reads the password that is not being displayed on the console.

How to get the object of Console

System class provides a static method console() that returns the unique instance of Console class.

1. public static Console console(){}  

Let's see the code to get the instance of Console class.

1. Console c=System.console();  

Java Console Example

import java.io.*;  

class ReadStringTest{  

public static void main(String args[]){  

Console c=System.console();  

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

String n=c.readLine();  

System.out.println("Welcome "+n);  

}  

}  

Output:

Enter your name: james gosling

Welcome james gosling

Java Console Example to read password

import java.io.*;  

class ReadPasswordTest{  

public static void main(String args[]){  

Console c=System.console();  

System.out.println("Enter password: ");  

char[] ch=c.readPassword();  

String pass=String.valueOf(ch);//converting char array into string  

System.out.println("Password is: "+pass);  

}  

}   

Output:

Enter password:

Password is: sonoo

Java Scanner class: There are various ways to read input from the keyboard; the java.util.Scanner class is one of them. The Java Scanner class breaks the input into tokens using a delimiter that is whitespace bydefault. It provides many methods to read and parse various primitive values. Java Scanner class is widely used to parse text for string and primitive types using regular expression. Java Scanner class extends Object class and implements Iterator and Closeable interfaces.

Commonly used methods of Scanner class:  There is a list of commonly used Scanner class methods.

Method	Description
public String next()	it returns the next token from the scanner.
public String nextLine()	it moves the scanner position to the next line and returns the value as a string.
public byte nextByte()	it scans the next token as a byte.
public short nextShort()	it scans the next token as a short value.
public int nextInt()	it scans the next token as an int value.
public long nextLong()	it scans the next token as a long value.
public float nextFloat()	it scans the next token as a float value.
public double nextDouble()	it scans the next token as a double value.

Java Scanner Example to get input from console

Let's see the simple example of the Java Scanner class which reads the int, string and double value as an input:

import java.util.Scanner;  

class ScannerTest{  

 public static void main(String args[]){  

   Scanner sc=new Scanner(System.in);  

     

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

   int rollno=sc.nextInt();  

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

   String name=sc.next();  

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

   double fee=sc.nextDouble();  

   System.out.println("Rollno:"+rollno+" name:"+name+" fee:"+fee);  

   sc.close();  

 }  

}   

Output:

       Enter your rollno

       111

       Enter your name

       Ratan

       Enter

       450000

       Rollno:111 name:Ratan fee:450000

Java Scanner Example with delimiter

Let's see the example of Scanner class with delimiter. The \s represents whitespace.

import java.util.*;  

public class ScannerTest2{  

public static void main(String args[]){  

     String input = "10 tea 20 coffee 30 tea buiscuits";  

     Scanner s = new Scanner(input).useDelimiter("\\s");  

     System.out.println(s.nextInt());  

     System.out.println(s.next());  

     System.out.println(s.nextInt());  

     System.out.println(s.next());  

     s.close();   

 }

}  

Output:

10

tea

20

coffee