title: what is Difference between keyword new and :(colon) symbol while creating the new instance of a class
body: <p>I have 2 class i want to import one class in </p>
  
  <p>Class students</p>
  
  <pre><code>export class students {
    public avr=123;
    constructor(a,b,c){}
  }
  </code></pre>
  
  <p>class college</p>
  
  <pre><code>import {students} from './commonwork'
  export class college{
    constructor(public abc:students){}
  }
  </code></pre>
  
  <p>This way works fine.</p>
  
  <p>But</p>
  
  <p>when I try to create the instance of class with new keyword in College class either in constructor or any where inside the class</p>
  
  <pre><code>var studentinstance= new student(){}
  </code></pre>
  
  <p>I get the error as "Expected 3 arguments, but got 0.ts(2554)"</p>
  
  <p>Can some one please explain the difference creating the instance with new keyword and :(colon) </p>