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Answer:

The different constructors require different parameters. (Different types of data are supplied to the constructors.)

Multiple Constructors

Any of the three constructors can be used to create a Point. It is a matter of convenience which constructor you use. Here is an example:

import java.awt.*;      // import the package that contains Point
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 );         // create a Point containing data equivalent
                                // to the data referenced by "b"
  }
}

To use the definition of class Point, import the package that contains it. The statement:

import java.awt.*

says to use the AWT package that comes with Java. The * says that everything defined in the package 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?