|  Welcome to JShell -- Version 14.0.1
|  For an introduction type: /help intro

jshell> Rectangle r = new Rectangle(6,8);
|  Error:
|  cannot find symbol
|    symbol:   class Rectangle
|  Rectangle r = new Rectangle(6,8);
|  ^-------^
|  Error:
|  cannot find symbol
|    symbol:   class Rectangle
|  Rectangle r = new Rectangle(6,8);
|                    ^-------^

jshell> /open Shape.java

jshell> /open Rectangle.java

jshell> Rectangle r = new Rectangle(6,8);
r ==> Rectangle@1d56ce6a

jshell> r.area()
$4 ==> 48.0

jshell> r.diameter()
$5 ==> 10.0

jshell> r.perimeter()
$6 ==> 28.0

jshell> Shape s = new Rectangle(3,4);
s ==> Rectangle@238e0d81

jshell> s.area()
$8 ==> 12.0

jshell> s.perimeter()
$9 ==> 14.0

jshell> s.diameter()
$10 ==> 5.0

jshell> //Rectangle is a subtype of Shape.

jshell> //Shape is a supertype of Rectangle

jshell> /exit
|  Goodbye
(base) MAC:Mon Nov 09:14:04:shapeF> vi Rectangle.java
(base) MAC:Mon Nov 09:14:05:shapeF> javac Rectangle.java
Rectangle.java:28: error: class, interface, or enum expected
}
^
1 error
(base) MAC:Mon Nov 09:14:05:shapeF> !vi
vi Rectangle.java
(base) MAC:Mon Nov 09:14:05:shapeF> !j
javac Rectangle.java
(base) MAC:Mon Nov 09:14:05:shapeF> !vi
vi Rectangle.java
(base) MAC:Mon Nov 09:14:12:shapeF> javac *.java
(base) MAC:Mon Nov 09:14:12:shapeF> ls
Circle.class    Rectangle.class Shape.class     eat_shorts.py
Circle.java     Rectangle.java  Shape.java
(base) MAC:Mon Nov 09:14:12:shapeF> jshell
|  Welcome to JShell -- Version 14.0.1
|  For an introduction type: /help intro

jshell> Shape s = new Rectangle(6,8);
|  Error:
|  cannot find symbol
|    symbol:   class Shape
|  Shape s = new Rectangle(6,8);
|  ^---^
|  Error:
|  cannot find symbol
|    symbol:   class Rectangle
|  Shape s = new Rectangle(6,8);
|                ^-------^

jshell> /open Shape.java

jshell> /open Rectangle.java

jshell> /open Circle.java

jshell> Shape s = new Rectangle(6,8);
s ==> Rectangle(6.0, 8.0)

jshell> s.area()
$5 ==> 48.0

jshell> s = new Circle(10);
s ==> Circle(10.0)

jshell> ArrayList<Shape> al = new ArrayList<>();
al ==> []

jshell> al.add(new Circle(10));
$8 ==> true

jshell> al.add(new Rectangle(10,10));
$9 ==> true

jshell> double out;
out ==> 0.0

jshell> for(Shape t: al)
   ...> {
   ...> out += al.area();
   ...> }
|  Error:
|  cannot find symbol
|    symbol:   method area()
|  out += al.area();
|         ^-----^

jshell> for(Shape t: al)
   ...> {
   ...> out += t.area();
   ...> }

jshell> out
out ==> 414.1592653589793

jshell> /exit
|  Goodbye
(base) MAC:Mon Nov 09:14:16:shapeF> vi Triangle.java
(base) MAC:Mon Nov 09:14:29:shapeF> javac Triangle.java
(base) MAC:Mon Nov 09:14:30:shapeF> ls
Circle.class    Polygon.class   Rectangle.java  Shape.java      Triangle.java
Circle.java     Rectangle.class Shape.class     Triangle.class  eat_shorts.py
(base) MAC:Mon Nov 09:14:35:shapeF> javac *.java
(base) MAC:Mon Nov 09:14:35:shapeF> jshell
|  Welcome to JShell -- Version 14.0.1
|  For an introduction type: /help intro

jshell> /open Shape.java

jshell> /open Polygon.java
|  File 'Polygon.java' for '/open' is not found.

jshell> /open Polygon.java
|  File 'Polygon.java' for '/open' is not found.

jshell> /open Polygon.java
|  File 'Polygon.java' for '/open' is not found.

jshell> /exit
|  Goodbye
(base) MAC:Mon Nov 09:14:36:shapeF> ls
Circle.class    Polygon.class   Rectangle.java  Shape.java      Triangle.java
Circle.java     Rectangle.class Shape.class     Triangle.class  eat_shorts.py
(base) MAC:Mon Nov 09:14:36:shapeF> ls
Circle.class    Polygon.java    Shape.class     Triangle.java
Circle.java     Rectangle.class Shape.java      eat_shorts.py
Polygon.class   Rectangle.java  Triangle.class
(base) MAC:Mon Nov 09:14:37:shapeF> jshell
|  Welcome to JShell -- Version 14.0.1
|  For an introduction type: /help intro

jshell> /open Polygon.java

jshell> /open Shape.java

jshell> /open Circle.java

jshell> /open Triangle.java

jshell> /opewn Rectangle.java
|  Invalid command: /opewn
|  Type /help for help.

jshell> /open Rectangle.java

jshell> Shape s = new Rectangle(6,8)
s ==> Rectangle(6.0, 8.0)

jshell> s.area()
$7 ==> 48.0

jshell> s.toString()
$8 ==> "Rectangle(6.0, 8.0)"

jshell> s.diameter()
$9 ==> 10.0

jshell> Polygon p = new Triangle(3,4,5);
p ==> Triangle(3.0, 4.0, 5.0)

jshell> p.area()
$11 ==> 6.0

jshell> p.diameter()
$12 ==> 5.0

jshell> p.perimeter()
$13 ==> 12.0

jshell> p.numSides()
$14 ==> 3

jshell> Object o = new Triangle(3,6,7);
o ==> Triangle(3.0, 6.0, 7.0)

jshell> o.toString()
$16 ==> "Triangle(3.0, 6.0, 7.0)"

jshell>