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Creating an abstract class to get perimeter and area?

The problem I was given:
Write an abstract superclass encapsulating a shape: a shape has 2 abstract methods: one returning the perimeter of the shape, another returning the area of the shoe. It also has a constant field named PI. This class has two non-abstract subclasses: one encapsulating a circle, and the other encapsulating a rectangle. A circle has one additional attribute, its radius. A rectangle has 2 additional attributes, its width and height. You also need to include a client class to test these two classes.
Here's the work I've done:
Shape.java
public abstract class Shape
{
public abstract double getPerimeter();
public abstract double getArea();
}
Circle.java
public class Circle extends Shape
{
private double radius;
final double pi = Math.PI;
//Defualt Constructor, calls Shape default constructor
public Circle()
{
//Set default value to radius
this.radius = 1;
}
public Circle(double radius)
{
this.radius = radius;
}
public double getArea()
{
//Return πr^2 (area formula)
//Use Math.pow method (page 141) in order to calculate exponent
return (pi * Math.pow(radius, 2));
}
public double getPerimeter()
{
//Return 2πr (perimeter formula)
return (2 * pi * radius);
}}
Rectangle.java
public class Rectangle extends Shape
{
private double width, height;
public Rectangle()
{
//set default value to width and height
this.width = 1;
this.height = 1;
}
public Rectangle(double width, double height)
{
this.width = width;
this.height = height;
}
public double getArea()
{
return width * height;
}
public double getPerimeter()
{
return 2 * (width + height);
}}
ShapeClient.java
public class ShapeClient {
public static void main(String [] args)
{
// To test Rectangle...
double width = 13, length = 9;
Shape rectangle = new Rectangle(width, length);
System.out.println("The rectangle width is: " + width
+ " and the length is: " + length
+ "The area is: " + rectangle.getArea()
+ "and the perimeter is: " + rectangle.getPerimeter() + ".");
//To test Circle...
double radius = 3;
Shape circle = new Circle(radius);
System.out.println("The radius of the circle is: " + radius
+ "The area is: " + circle.getArea()
+ "and the perimeter is: " + circle.getPerimeter() + ".");
}}
My question is: Does the constant field for PI need to be in the Shape class rather than the Circle class? If so, how should I about taking it out of the circle class and how should I place it in the Shape class?

The abstract class should only contain fields & methods that are general to all shapes such as getArea and getPerimeter.
In this case PI is only specific to the Circle shape or to rephrase, the square has no use for the constant PI. PI should therefore only reside in the 'Circle' class and not the Shape class.

The PI attribute definitely needs to be on the Circle class. The abstract Shape class should contain attributes and methods that all of its sub-classes are going to use or implement. In this case, the Rectangle class has no need for the PI attribute.

just move the constant to the abstract class.

Printf Statement

Is there a way to have the radius shown in this printf statement located at the bottom? So far, I only have the area shown.
public class Circle
{
private double radius;
private double Area;
public void setRadius(double rad)
{
radius = rad;
}
public void calculateArea( )
{
Area=Math.PI*(radius*radius);
}
public void printArea( )
{
System.out.printf("A Circle of radius has area %.4f", Area);
System.out.println();
}
}

I am assuming you want to show the radius in the print statement. You are already having it in the field 'radius' right..so can you not do something like
System.out.println("A Circle of radius " + radius + " has area " + Area);

You can use the following code
System.out.printf("A Circle of radius %4f has area %.4f", radius, Area);
Also to effectively use printf and format methods, just check out the documentation

How to assign an object property value to a variable in Java?

The following code is what I'm having issues understanding:
public class Rectangle {
public Rectangle() {
double width = 1;
double height = 1;
}
public Rectangle(double w, double h) {
double width = w;
double height = h;
}
public double getArea(double w, double h) {
return (w*h);
}
public double getPerimeter(double w, double h) {
return ((2*w)+(2*h));
}
public static void main(String[] args) {
Rectangle oldRectangle = new Rectangle(4, 40);
Rectangle newRectangle = new Rectangle(3.5, 35.9);
double height1 = oldRectangle.height;
double height2 = newRectangle.height;
double width1 = oldRectangle.width;
double width2 = newRectangle.width;
System.out.println("Width of Rectangle 1 is: " + 4);
System.out.println("Height of Rectangle 1 is: " + 40);
System.out.println("Area of Rectangle 1 is: " + oldRectangle.getArea(4, 40));
System.out.println("Perimeter of Rectangle 1 is: " + oldRectangle.getPerimeter(4, 40));
System.out.println("Width of Rectangle 1 is: " + 3.5);
System.out.println("Height of Rectangle 1 is: " + 35.9);
System.out.println("Area of Rectangle 1 is: " + newRectangle.getArea(3.5, 35.9));
System.out.println("Perimeter of Rectangle 1 is: " + newRectangle.getPerimeter(3.5, 35.9));
}
}
I was instructed to create two constructors for a Rectangle class—one with no arguments but assigned a default value of 1 for both variables width and height. The second constructor was to contain parameters that would take in two doubles that would get assigned to their appropriate variable.
I was then told to create two 'get()' methods that returned their respective values—in my case, they were perimeter and area of said Rectangle.
I was then instructed to create two Rectangle instances, one with a width of 4 and a height of 40—and another with a width of 4.5 and a height of 35.9. So, I did just that and made two new Rectangle objects, as you can see.
Lastly, I was instructed to print out the Width, Height, Perimeter, and Area of both Rectangle objects. My issue is that I don't know of a way to reference them. I took a beginners tutorial class for JavaScript and if I'm not mistaken, I recall there was a way to reference a property value of an object by assigning it to a variable. Again, I'm saying "If I'm not mistaken", so I could be wrong. It's been a while...
I do realize that Java and Java Script are entirely different things in their own right. Java Script was a scripting language developed and based off of Java.
Anyway, any help will be grand.
Please feel free to help me understand how I can implement what I'm trying to do by giving examples. You don't have use my exact code, but I'd like to be able to get my code to make more sense.. I'm using Eclipse btw.

You are on the right track. What you are looking to do is something like this:
public double getArea(Rectangle r){
return r.width*r.height;
}
public double getPerimeter(Rectangle r){
return (2*r.width + 2*r.height);
}
For the print statements you are hard-coding in values which you dont have to do.
System.out.println("Width of Rectangle 1 is: " + oldRectangle.width);
System.out.println("Height of Rectangle 1 is: " + oldRectangle.height);
System.out.println("Area of Rectangle 1 is: " + getArea(oldRectangle));
System.out.println("Perimeter of Rectangle 1 is: " + getPerimeter(oldRectangle));

My issue is that I don't know of a way to reference them
As Java is a strong-typed language, to store the references to each Rectangle (or any object) attribute, you must create variables that match the field.
First, you need your rectangle have attributes:
public class Rectangle {
public double width;
public dobule height;
// constructors here...
After, methods to calculate area and perimeter:
public double getArea() {
return (width*height);
}
public double getPerimeter() {
return ((2*width)+(2*height));
}
Now, to reference them (i guess you still mean area and perimeter):
double area1 = getArea(newRectangle);
double area2 = getArea(oldRectangle);
and
double perimeter1 = getPerimeter(newRectangle);
double perimeter2 = getPerimeter(oldRectangle);

There are no width and height properties in your class, they are only defined inside the constructor, declare them in the class and not inside the constructors so you can acces them like this:
public class Rectangle {
double width;
double height;
public Rectangle() {
width = 1;
height = 1;
}
public Rectangle(double w, double h) {
width = w;
height = h;
}
public double getArea(double w, double h) {
return (w*h);
}
public double getPerimeter(double w, double h) {
return ((2*w)+(2*h));
}
//....
}
Note: It's better to declare them as private and use getters and setters to acces them, take a look at Adding Setter and Getter Methods for further information.
EDIT:
In your case you don't need to pass parameters to your methods (because the calculation needs this rectangle width and height), just calculate them using your class fields, like this:
public double getArea() {
return (width*height);
}
public double getPerimeter() {
return ((2*width)+(2*height));
}
Here's what you need to do to acces your variables:
public static void main(String[] args) {
Rectangle oldRectangle = new Rectangle(4, 40);
Rectangle newRectangle = new Rectangle(3.5, 35.9);
//In the following you access all the object variables and methods
System.out.println("Width of Rectangle 1 is: " + oldRectangle.width);
System.out.println("Height of Rectangle 1 is: " + oldRectangle.height);
System.out.println("Area of Rectangle 1 is: " + oldRectangle.getArea());
System.out.println("Perimeter of Rectangle 1 is: " + oldRectangle.getPerimeter());
System.out.println("Width of Rectangle 1 is: " + newRectangle.width);
System.out.println("Height of Rectangle 1 is: " + newRectangle.height);
System.out.println("Area of Rectangle 1 is: " + newRectangle.getArea());
System.out.println("Perimeter of Rectangle 1 is: " + newRectangle.getPerimeter());
}
You can test the DEMO here.
And to answer your question about using constructor, calling the parametrized constructor like this:
Rectangle oldRectangle = new Rectangle(4, 40);
Is equivalent to:
// create the object
Rectangle oldRectangle = new Rectangle();
//And then assigning the values 4 and 40 to its width and height
oldRectangle.width=4;
oldRectangle.height=40;

Cannot find symbol: Circle Error

I have written the following code and keep getting the error:
error: cannot find symbol
Circle first = new Circle();
^
symbol: class Circle
location: class TestCircle
error: cannot find symbol
Circle first = new Circle();
^
symbol: class Circle
location: class TestCircle
This is repeated for the second and third as well. Here are the codes:
public class TestCircle {
/**
* #param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
// Create three Circle objects
Circle first = new Circle();
Circle second = new Circle();
Circle third = new Circle();
// Initialize radius for first and second circles
first.setRadius(6.0);
second.setRadius(15.0);
// Display circle Info
first.displayCircle();
second.displayCircle();
third.displayCircle();
}
}
public class Circle {
//
private double radius; // circle radius
private double diameter; // circle diameter
private double area; // circle area
private final double pi = 3.14159265358979; // value of pi
Circle() // Constructor
{
radius = 1;
diameter = 2 * radius;
area = pi * radius * radius;
}
void setRadius(double rad) // method to set radius and calculate the other two values
{
radius = rad;
diameter = 2 * radius;
area = pi * radius * radius;
}
double getRadius() // method to get radius
{
return radius;
}
void displayCircle() // method to display circle parameters
{
System.out.println("Circle Info");
System.out.println("Radius: " + radius);
System.out.println("Diameter: " + diameter);
System.out.println("Area: " + area);
}
}
Any help in solving this is appreciated.

You need to make your constructor public.
If you don't make it public, then it can only be accessed within the package which is the reason for your error.

It appears that Circle is probably in a different package than TestCircle. If that's the case (if Circle.java has package abcde; or something at the top), then TestCircle will need to import it:
import abcde.Circle;
And, the constructor and all the methods in Circle have to be made public, since the default access ("package-private") doesn't work for a class that's in a different package.
If Circle doesn't have a package statement, then things should work if TestCircle.java and Circle.java are in the same directory. If they're in different directories, but they don't have package statements, then I think you will need to set the CLASSPATH so that it can refer to all the directories where classes exist, or if you're using an IDE, configure it to find things in a different directory. But I'd recommend either using packages or putting things in the same directory.

It's not mandatory to add public before the package. But for a best practice you should make each class in a separate file. And it will work. Try this:
Circle class :
public class Circle {
private double radius; // circle radius
private double diameter; // circle diameter
private double area; // circle area
private final double pi = 3.14159265358979; // value of pi
public Circle() { // Constructor
radius = 1;
diameter = 2 * radius;
area = pi * radius * radius;
}
void setRadius(double rad) // method to set radius and calculate the other two values
{
radius = rad;
diameter = 2 * radius;
area = pi * radius * radius;
}
double getRadius() // method to get radius
{
return radius;
}
void displayCircle() // method to display circle parameters
{
System.out.println("Circle Info");
System.out.println("Radius: " + radius);
System.out.println("Diameter: " + diameter);
System.out.println("Area: " + area);
}
}
TestCircle class:
public class TestCircle {
/**
* #param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
// Create three Circle objects
Circle first = new Circle();
Circle second = new Circle();
Circle third = new Circle();
// Initialize radius for first and second circles
first.setRadius(6.0);
second.setRadius(15.0);
// Display circle Info
first.displayCircle();
second.displayCircle();
third.displayCircle();
}
}
Notice
If you want to use a single file don't forget to remove the word public before class Circle. Because each class which declared as public should be in a new separate file.

Java object returning zeros for calculated variables

this is my first question here and I'm very new to programming so please bear with me.
I'm taking a java class, and in my current assignment I have to create three instances of a circle, compute their diameters and areas, and print the values. The first two instances are supposed to have the radius set by a setRadius method, while the third is supposed to retain the default calculations based on a radius of 1.
edit: The problem is this: the first two objects, on which I used the setRadius method, returned correct values, but the third was intended to return default values of the constructor, and instead it returned all zeros.
Here is the code, thanks in advance!
//this class implements the Circle class
public class TestCircle
{
public static void main(String[] args)
{
Circle Circle1 = new Circle();
Circle Circle2 = new Circle();
Circle Circle3 = new Circle();
Circle1.setRadius(2);
Circle2.setRadius(10);
Circle1.display();
Circle2.display();
Circle3.display();
}
}
import java.lang.Math.*;
public class Circle
{
double radius;
double diameter;
double area;
public void Circle()
{
radius = 1;
diameter = radius * 2;
area = (radius * radius) * Math.PI;
}
public void setRadius(double rad)
{
this.radius = rad;
diameter = radius * 2;
area = (radius * radius) * Math.PI;
}
public void display()
{
System.out.println("Radius: " + radius);
System.out.println("Diameter: " + diameter);
System.out.println("Area: " + area);
}
}

This
public void Circle()
is just a method with a void return type. For a constructor, you need
public Circle() // notice there is no return type
Because you didn't actually provide a constructor, the following
Circle Circle1 = new Circle();
Circle Circle2 = new Circle();
Circle Circle3 = new Circle();
used a default constructor provided by the compiler. It has an empty body and thus the field values are all initialized to 0 by default.
And since you only call setRadius() on two of them, the other one will only show values of 0.
Read up on constructors here.
Java naming conventions state that variable names should start with lowercase letters and follow a camelCase format. You can do some further reading on this subject here.