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Aug 7, 2014

How to capture user input in Java or interact with user via command line

#1: Using the System.console( ) . This will not work within eclipse IDE. You can try it on a DOS or Unix command-line.

package com.user.input;

import java.io.Console;

public class Example1 {
 
  public static void main(String[] args) {
   Console console = System.console();
   String input = console.readLine("What is your name:");
   System.out.println("User input = " + input);
 }
}

The output:

C:\temp>java -cp C:\Users\akumaras\workspace\test\bin com.user.input.Example1

What is your name:Arul
User input = Arul

C:\Users\akumaras\workspace\test\bin\com\user\input>


#2: The Scanner class.

package com.user.input;

import java.io.Console;
import java.util.Scanner;

public class Example2 {
 
  public static void main(String[] args) {
   Scanner reader = new Scanner(System.in);
   System.out.println("Enter first operand?");
   int operand1=reader.nextInt();
   
   System.out.println("Enter second operand?");
   int operand2=reader.nextInt();
   
   System.out.println("The sum is: " + (operand1 + operand2));
 }
}


The output:

Enter first operand?
5
Enter second operand?
6
The sum is: 11


#3: Decorating System.in with BufferedReader and SystemInputReader.

package com.user.input;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Example3 {
 
  public static void main(String[] args) throws NumberFormatException, IOException {
   //System.in is decorated with InputStreamReader and BufferedReader
   //buffering is required for efficiency
   BufferedReader br = new BufferedReader( new InputStreamReader(System.in));
   
   System.out.println("Enter first operand?");
   int operand1 = Integer.parseInt(br.readLine());
  
     
   System.out.println("Enter second operand?");
   int operand2=Integer.parseInt(br.readLine());
   
   System.out.println("The sum is: " + (operand1 + operand2));
 }
}


The output:

package com.user.input;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Example3 {
 
  public static void main(String[] args) throws NumberFormatException, IOException {
   //System.in is decorated with InputStreamReader and BufferedReader
   //buffering is required for efficiency
   BufferedReader br = new BufferedReader( new InputStreamReader(System.in));
   
   System.out.println("Enter first operand?");
   int operand1 = Integer.parseInt(br.readLine());
  
     
   System.out.println("Enter second operand?");
   int operand2=Integer.parseInt(br.readLine());
   
   System.out.println("The sum is: " + (operand1 + operand2));
 }
}


Note: You can also decorate it with DataInputStream. A good example of the decorator design pattern implemented in the Java I/O API.


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