class B {} // some class

class A
{
  B b = new B(); // composition - every A instance contains a B object

  void someMethod()
  {
    B c = new B();
    // not composition - it is a local variable
    // a B object is temporarily constructed on the stack when this method executes
    // and ends when this method ends.
    // It is not part of an A object

  }
}