title: How to read input with multiple lines in Java
body: <p>Our professor is making us do some basic programming with Java, he gave a website and everything to register and submit our questions, for today I need to do this one example I feel like I'm on the right track but I just can't figure out the rest. Here is the actual question:</p>
  
  <pre><code>**Sample Input:**
  10 12
  10 14
  100 200
  
  **Sample Output:**
  2
  4
  100
  </code></pre>
  
  <p>And here is what I've got so far :</p>
  
  <pre><code>public class Practice {
  
      public static int calculateAnswer(String a, String b) {
          return (Integer.parseInt(b) - Integer.parseInt(a));
      }
  
      public static void main(String[] args) {
          System.out.println(calculateAnswer(args[0], args[1]));
      }
  }
  </code></pre>
  
  <p>Now I always get the answer <code>2</code> because I'm reading the single line, how can I take all lines into account? thank you</p>
  
  <p>For some strange reason every time I want to execute I get this error:</p>
  
  <pre><code>C:\sonic&gt;java Practice.class 10 12
  Exception in thread "main" java.lang.NoClassDefFoundError: Fact
  Caused by: java.lang.ClassNotFoundException: Fact.class
          at java.net.URLClassLoader$1.run(URLClassLoader.java:20
          at java.security.AccessController.doPrivileged(Native M
          at java.net.URLClassLoader.findClass(URLClassLoader.jav
          at java.lang.ClassLoader.loadClass(ClassLoader.java:307
          at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.
          at java.lang.ClassLoader.loadClass(ClassLoader.java:248
  Could not find the main class: Practice.class.  Program will exit.
  </code></pre>
  
  <p>Whatever version of answer I use I get this error, what do I do ?</p>
  
  <p>However if I run it in eclipse Run as > Run Configuration -> Program arguments </p>
  
  <pre><code>10 12
  10 14
  100 200
  </code></pre>
  
  <p>I get no output</p>
  
  <p><strong>EDIT</strong> </p>
  
  <p>I have made some progress, at first I was getting the compilation error, then runtime error and now I get wrong answer, so can anybody help me what is wrong with this:</p>
  
  <pre><code>import java.io.BufferedReader;
  import java.io.IOException;
  import java.io.InputStreamReader;
  import java.math.BigInteger;
  
  public class Practice {
  
      public static BigInteger calculateAnswer(String a, String b) {
          BigInteger ab = new BigInteger(a);
          BigInteger bc = new BigInteger(b);
          return bc.subtract(ab);
      }
  
      public static void main(String[] args) throws IOException {
          BufferedReader stdin = new BufferedReader(new InputStreamReader(System.in)); 
          String line; 
  
          while ((line = stdin.readLine()) != null &amp;&amp; line.length()!= 0) { 
              String[] input = line.split(" "); 
              if (input.length == 2) { 
                  System.out.println(calculateAnswer(input[0], input[1])); 
              } 
          } 
      }
  }
  </code></pre>