Difference between instantiate object in class and in constructor of class?

in the first one, your cl is a member variable and every method in the class will have access to it.

In the second one, cl is only available to the scope of the constructor so other methods won't be able to access it. 


What I usually do is I declare the object as a member variable and instantiate it with "new" in the constructor.  This way, you could instantiate for different constructors

public class classA
{
   private classB m_myClass;
 
   public classA()
   {
      m_myClass = new classB();
   }
  
   public classA(int Value)
   {
        m_myClass = new classB(Value);
   }
}