Integer Input

(It would not be too surprising if you forgot that.) Here is a program that computes the square of a number that the user enters. It uses the one-line method of constructing a BufferedReader.

import java.io.*;
class EchoSquare
{
  public static void main (String[] args) throws IOException
  { 
    BufferedReader stdin = 
      new BufferedReader (new InputStreamReader(System.in));
 
    String inData;
    int    num, square;    // declare two int variables

    System.out.println("Enter an integer:");
    inData = stdin.readLine();
    
    num    = Integer.parseInt( inData ); // convert inData to int
    square = num * num ;                 // compute the square

    System.out.println("The square of " + inData + " is " + square);
  }
}

This program is the previous program with a few additions (in blue). You can copy-paste-and-run it. Better yet, study it for a while, then go to NotePad and see how much you can reconstruct. Now look at this statement:

num  = Integer.parseInt( inData );  // convert inData to int

This uses the method parseInt() of the Integer wrapper class. This method takes a String containing an integer in character form. It looks at those characters and calculates an int value. That value is assigned to num.

num = Integer.parseInt( "39" );