What is the difference in the constructors?

A good answer might be:

Each constructor requires the user to supply different data.

Multiple Constructors

Any of the three constructors can be used to instantiate a Point. (Remember that "instantiate" means "create an object.") It is a matter of convenience which constructor you use. Here is a program that instantiates some points: 
import java.awt.*;      // import the class library where Point is defined
class pointEg1
{

  public static void main ( String arg[] )
  {
    Point a, b, c;              // reference variables

    a = new Point();            // create a Point at ( 0,  0); save the reference in "a"
    b = new Point( 12, 45 );    // create a Point at (12, 45); save the reference in "b"
    c = new Point( b );
  }
}

For the compiler to be able to use the definition of Point in the class library, an import must be used. The statement
import java.awt.* says to use the AWT library that is part of java. The "*" says that everything defined in the library can be used (although this program only uses the Point class.)

QUESTION 4:

Say that the program has just been loaded into main memory and is just about to start running.
How many reference variables are there?
How many objects are there?

Click Here after you have answered the question