title: is System.in an object reference of InputStream class?
body: <p>InputStream is an Abstract class.Then how are we able to access System.in.And moreover int read() is an abstract method in InputStream class.Then how are we able to access System.in.read() method if read() is an abstract method.
  Like </p>
  
  <pre><code>int a=System.in.read();
  System.out.println((char)a); 
  </code></pre>