I'm currently undertaking a Java class (one of my final ones for my bachelor, yay) and I'm having a really difficult time trying to understand classes and do this problem below. The textbook I'm currently using is quite confusing and I've tried to use other online resources to figure out what I'm doing wrong but I still seem stuck on the question below. Whenever I try and run the program all I get is 0.00.0 for my answer, is this due to myself incorrectly assigning values to cylinder1? Also, for the toString() class how do I even go about doing this? I'm always getting errors on converting doubles to Strings no matter what I can do.
Any help would be appreciated it.
Thanks.
Prompt
Implement the class called Cylinder shown in UML below. The constructor accepts and initializes the radius and height for the Cylinder, while accessors and mutators allow them to be changed after object construction. The class also include methods that calculate and return the volume and surface area of the Cylinder. Lastly, it contains a toString method that returns the name of the shape, its radius, and its height. Create a main method which instantiates 4 Cylinder objects (any parameters), display them with toString(), change one parameter (your choice) in each, and display them again. [15 points]
UML
Code
import java.util.*;
import java.text.*;
import java.io.*;
import java.lang.*;
class Cylinder
{
private double radius, height, area, volume;
public Cylinder(double height, double radius) {
radius = 0.0;
height = 0.0;
}
public double getRadius() {
return radius;
}
public double getHeight() {
return height;
}
public double getArea() {
double area = (2 * Math.PI * radius * height) + (2 * Math.PI * Math.pow(radius, 2));
return area;
}
public void setRadius(double r) {
radius = r;
}
public void setHeight(double h) {
height = h;
}
public double calcVolume() {
double volume = Math.PI * Math.pow(radius, 2) * height;
return volume;
}
public String toString (){
StringBuilder StBuild = new StringBuilder();
StBuild.append(radius).append(height);
return StBuild.toString();
}
public static void main(String[] args) {
Cylinder cylinder1 = new Cylinder(5, 5);
System.out.println(cylinder1);
}
}
Since this is obviously homework I won't give you the answers, but I'll try to explain a few things.
This:
public Cylinder(double height, double radius) {
radius = 0.0;
height = 0.0;
}
is a constructor. When you create an object (and instance of a class) you call this. You call it by doing:
Cylinder cylinder1 = new Cylinder(5, 5);
But what happens in your class? When you call the constructor are you really saving the values you want?
As for the toString method, you could either call the toString for the double (height.toString) or you could just do what I always end up doing which is just cheat by adding a string to it.
public String toString (){
return "Cylinder [ h: " + height + " - r: " + radius + " - v: " + calcValume() + "]";
}
in class Cylinder change the constructor to:
public Cylinder(double height, double radius) {
this.radius = radius;
this.height = height;
}
In void main() :
Cylinder cylinder1 = new Cylinder(5, 5);
System.out.println(cylinder1.calcVolume());
This will work.
But you should shift the main method to some other class.
In the constructor you are setting the radius and height to 0.0. Try:
public Cylinder(double height, double radius) {
this.radius = radius.
this.height = height;
}
Related
I am new to Java and currently doing a small project to learn.
These are the requirements for the project:
Create a class named Circle with a field named radius.
Include default constructor
Include a default constructor that sets the radius to 1 by default.
Include another constructor that receives the radius and sets the radius to the value
received.
Include a method that returns the area of the circle.
-Include another method that returns the circumference of the circle.
Use the PI constant of the Math class for this calculation.
Create a class named TestCircle whose main() method declares 5 Circle objs and stores them in an array
5 circle objects will have different radius values
Using a loop, iterate the objects and display areas and circumference of the objects from the array
if the radius is one, display a message saying "This is a unit circle".
I managed to complete some of the requirements to the best of my ability but I don't know how to
Using a loop, iterate the objects and display areas and circumference of the objects from the array. If the radius is one, display a message saying "This is a unit circle".
class Circle {
double radius;
//constructor to default radius to 1
public Circle() {
this.radius = 1;
}
//constructor to receive values and set it as radius
public Circle(double [] circlesRad) {
this.radius = circlesRad[0];
}
public double computeArea(){
return Math.PI * (radius * radius);
}
public double computeCircumference() {
return Math.PI *2*radius;
}
}
public class TestCircle {
public static void main(String[] args) {
Circle c1 = new Circle();
double circlesRad[] = {1, 34, 56, 23, 93, 18};
for (double rad : circlesRad) {
System.out.println("Circle:"+"\nArea: "+ c1.computeArea()+"\nCircumference: "+ c1.computeCircumference());
if (rad == 1){
System.out.println("Circle:"+"\nArea: "+ c1.computeArea()+"\nCircumference: "+ c1.computeCircumference());
System.out.println("This is a unit circle.");
}
}
}
}
I know its very wrong, and I apologise.
Any help would be much appreciated.
Below is the code:-
class Circle {
double radius;
//constructor to default radius to 1
public Circle() {
this.radius = 1;
}
//you should consider this as just passing a radius value.
public Circle(double circlesRad) {
this.radius = circlesRad;
}
public double getRadius() {
return radius;
}
public void setRadius(double radius) {
this.radius = radius;
}
public double computeArea(){
return Math.PI * (radius * radius);
}
public double computeCircumference() {
return Math.PI *2*radius;
}
}
public class TestCircle {
public static void main(String[] args) {
Circle[] circles = {new Circle(1), new Circle(34), new Circle(56),
new Circle(23), new Circle(93), new Circle(18)};
for (Circle circle : circles) {
System.out.println("Circle:"+"\nArea: "+ circle.computeArea()+"\nCircumference: "+ circle.computeCircumference());
if (circle.getRadius() == 1){
System.out.println("This is a unit circle.");
}
}
}
}
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.
I have a home work in a java... I tried many ways, but, apparently, stackoverflow is a last :(
So, I have this class:
public final class Span {
private final double length;
public Span(){
this(0);
}
public Span(double length) {
this.length= length;
}
public double getLength(){
return length;
}
}
public final class Circle {
private Span radius;
//radius with double
public Circle(double radius) {
}
// span
public Circle(Span radius){
this.radius= radius;
}
//calculate area.....
public double area(double radius){
return Math.PI * (radius * radius);
}
But:
**private Span radius**; <---- This is necessary :(
I have to create Span(type) radius (in Circle class), Span diameter and Span perimeter.
public final class Circle {
private Span radius;
//radius with double
public Circle(double radius) {
this.radius = new Span(radius);
}
// span
public Circle(Span radius){
this.radius= radius;
}
//calculate area.....
public double area(){
return Math.PI * (radius.getLength() * radius.getLength());
}
It's hard to see much value in the Span class over and above a raw double. I can think of two features you could add that would make it more useful:
Negative lengths make no sense. I'd add a check in the Span constructor to the throw an IllegalArgumentException if a length less than zero is passed it prior to assignment.
Encapsulating units along with the length (cm, m, inches, feet, etc.) would be an improvement.
Having those, you just need to be able to calculate using spans:
double perimeter = 2.0*Math.PI*Span.getLength();
You should not be setting radius once you construct the Circle. Let it tell you what the area is using the original Span.
I'm supposed to find the volume of a cylinder using a Circle object I made in another class. When I create my getVolume method, it tells me I can't multiply a Circle and double, and wanted to know how to fix it. I can't make a getArea method in the Cylinder class, just make a new Circle using a user-inputted radius. Here's the code (first for the Circle class, and second the Cylinder class):
public class Circle {
private double radius;
public Circle(double r) {
radius = r;
}
public double getArea() {
return Math.PI * radius * radius;
}
}
public class Cylinder {
private Circle base;
private double height;
public Cylinder(double r, double h) {
base = new Circle(r);
height = h;
}
public double getVolume() {
return base * height;
}
}
So the getVolume method is my problem. How can I get the program to recognize "base" as a double while it is still a Circle object?
You wanted to write
public double getVolume() {
return base.getArea() * height;
}
Right?
Otherwise, just by thinking of it: do you multiply a circle with a length? No, you multiply an area with a length to get the volume...
Also, if the circle would have a name attribute too, what should be multiplied? There is no magic, the JVM does what you tell it to do.
You need to multiply the area of the circle by the height. But you can't multiply a Circle and a double. Call getArea() on your Circle.
return base.getArea() * height;
return base.getArea() * height
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.