Develop Reference

Must implement inherited abstract method error

I'm getting an error for Sphere.java that says
The type sphere must implement the inherited abstract method GeometricObjects.hit(Ray)
Though I don't see how I am getting this error as I've defined the hit method as shown below.
Below is the Sphere.java code:
package Objects;
import Utility.*;
public class Sphere extends GeometricObjects {
Point3d center;
double radius;
public Sphere(Point3d center, double radius, Color color) {
this.center = new Point3d(center);
this.radius = radius;
this.color = new Color(color);
}
public double hit(Ray ray) {
double a = ray.direction.dot(ray.direction);
double b = 2*ray.origin.sub(center).dot(ray.direction);
double c = ray.origin.sub(center).dot(ray.origin.sub(center)) - radius*radius;
double discriminant = b*b - 4*a*c;
if (discriminant < 0.0){
return 0.0;
}
else {
double t = (-b - Math.sqrt(discriminant)) / (2*a);
if (t > 10E-9) {
return t;
}
else {
return 0.0;
}
}
}
}
This is the GeometricObjects.java code:
package Objects;
import Utility.*;
public abstract class GeometricObjects {
public Color color;
public abstract double hit(Ray ray);
}
And heres the Ray.java code:
package Utility;
public class Ray {
public Point3d origin;
public Vector direction;
public Ray(Point3d origin, Vector direction) {
this.origin = new Point3d(origin);
this.direction = new Vector(direction);
}
}

Java - Cannot resolve constructor

I am new to Java programming. I have three classes which are Main, Point and Rectangle. I can use all constructors in Rectangle class except this one: Rectangle(Point p, int w, int h). Java compiler gives: "Cannot resolve constructor 'Rectangle(java.awt.Point, int, int)'" error. Thanks.
Here my classes:
Main.java
import java.awt.*;
import java.awt.Point;
import java.awt.Rectangle;
public class Main {
public static void main(String[] args) {
Point originOne = new Point(5,10);
Rectangle rectOne = new Rectangle(originOne, 100, 200);
}
}
Point.java
public class Point {
public int x = 0;
public int y = 0;
//contructor
public Point(int a, int b){
x = a;
y = b;
}
}
Rectangle.java
public class Rectangle {
public Point origin;
public int width = 0;
public int height = 0;
//four contructors
public Rectangle() {
origin = new Point(0, 0);
}
public Rectangle(Point p){
origin = p;
}
public Rectangle(int w, int h){
origin = new Point(0,0);
width = w;
height = h;
}
public Rectangle(Point p, int w, int h) {
origin = p;
width = w;
height = h;
}
// a method for moving the rectangle
public void move(int x, int y) {
origin.x = x;
origin.y = y;
}
//a method for computing the area of rectangle
public int getArea() {
return width * height;
}
}

Your answer is fairly simple. You've imported the wrong import, rather than import java.awt.Rectangle, import your own class.
By doing:
import <nameOfTheProject>.Rectangle;
If I had a project in Eclipse called MyShapes and had the same classes. I would import it like:
import MyShapes.Rectangle;
Now this obviously depends on how your file structure is, but if it's inside a sub-folder (sub-package), I would do like:
import MyShapes.ShapesClasses.Rectangle;
This also applies to the Point class if you're planning on using your own Point class and not Java.awt's one!

How to implement one generic method for two classes in java

I have an interface that has one ordinary method and one generic method. I have implemented ordinary method for two different classes, but do not now how to do that with generic method. Here is my code:
Sphere.java:
public class Sphere implements GeometricShape<Sphere> {
private double radius;
public Sphere (double radius) {
this.radius = radius;
}
public double volume() {
return (4.0 / 3.0) * Math.PI * radius * radius * radius;
}
public void describe() {
System.out.println("Sphere[radius=" + radius + "]");
}
#Override
public Sphere supersize()
{
this.radius*=2;
return new Sphere(radius);
}
}
Rectangle.java
public class Rectangle implements TwoDShape {
private double width, height;
public Rectangle (double width, double height) {
this.width = width;
this.height = height;
}
public double area()
{
return width * height;
}
public double perimeter()
{
return 2.0 * (width + height);
}
public void describe()
{
System.out.println("Rectangle[width=" + width + ", height=" + height + "]");
}
#Override
public Rectangle supersize()
{
this.width*=2;
this.height*=2;
return new Rectangle(width, height);
}
}
TwoDShape.java:
public interface TwoDShape extends GeometricShape
{
public double area();
}
ThreeDShape.java:
public interface ThreeDShape extends GeometricShape<ThreeDShape>
{
public double volume();
}
GeometricShape.java:
public interface GeometricShape<T extends GeometricShape<T>>
{
public void describe();
public T supersize();
}
and finally main class ArrayListExample.java:
import java.util.ArrayList;
public class ArrayListExample {
public static void describe_all( ArrayList<? extends GeometricShape> shapes )
{
for(int i=0;i<shapes.size();i++)
{
shapes.get(i).describe();
}
System.out.println("Total number of shapes:"+ shapes.size());
}
public static void main(String[] args) {
System.out.println("The describe() method:");
System.out.println();
System.out.println("Example rectangles");
ArrayList<Rectangle> rects = new ArrayList<Rectangle>();
rects.add(new Rectangle(2.0, 3.0));
rects.add(new Rectangle(5.0, 5.0));
describe_all(rects);
System.out.println();
ArrayList<Sphere> spheres = new ArrayList<Sphere>();
spheres.add(new Sphere(10.0));
spheres.add(new Sphere(50.0));
spheres.add(new Sphere(0.0));
System.out.println("Example spheres");
describe_all(spheres);
System.out.println();
System.out.println("The supersize() method:");
System.out.println();
ArrayList<Rectangle> double_rects = supersize_list(rects);
describe_all(double_rects);
System.out.println();
ArrayList<Sphere> double_spheres = supersize_list(spheres);
describe_all(double_spheres);
}
}
How can I implement supersize_list method that it takes supersize method from both rectangle and sphere and outputs like
Rectangle[width=4.0, height=6.0]
Rectangle[width=10.0, height=10.0]
Total number of shapes: 2
Sphere[radius=20.0]
Sphere[radius=100.0]
Sphere[radius=0.0]
Total number of shapes: 3
Could you help me with this, please? I greatly appreciate your help!

The class hierarchy looks inconsistent. For example, you have ThreeDShape extends GeometricShape<ThreeDShape> and TwoDShape extends GeometricShape at the same time, for no obvious reason. It's not fun to write a generic method for these types.
Here's a less-confusing version. (I hope) Note: I choose not to change the size of the shape itself in supersize method, instead let it return a bigger shape while keeping the original unchanged.
1. GeometricShape
/**
* A geometric shape interface. You can do two things with it.
* 1. Ask it to describe itself (to stdout);
* 2. Ask it to return a bigger version of itself (double the size).
*/
public interface GeometricShape<T extends GeometricShape<T>> {
/**
* Print a description to STDOUT
*/
void describe();
/**
* Returns a bigger shape.
* #return Something that's a GeometricShape
*/
T supersize();
}
2. Shape2D and Rectangle
/**
* A 2-dimensional shape.
* It has area.
* Its supersize() method should return a Shape2D instance.
*/
public interface Shape2D<T extends Shape2D<T>> extends GeometricShape<T> {
double area();
}
/**
* A rectangle.
*/
public final class Rectangle implements Shape2D<Rectangle> {
private final double width;
private final double height;
public Rectangle(double width, double height) {
this.width = width;
this.height = height;
}
#Override
public String toString() {
return "Rectangle{" +
"width=" + width +
", height=" + height +
'}';
}
#Override
public void describe() {
System.out.println(this);
}
#Override
public Rectangle supersize() {
return new Rectangle(width*2, height*2);
}
#Override
public double area() {
return width * height;
}
}
3. Shape3D and Sphere
/**
* A 3-dimensional shape.
* It has volume.
* Its supersize() method should return a Shape3D instance.
*/
public interface Shape3D<T extends Shape3D<T>> extends GeometricShape<T> {
double volume();
}
/**
* A sphere
*/
public final class Sphere implements Shape3D<Sphere> {
private final double radius;
public Sphere(double radius) {
this.radius = radius;
}
#Override
public String toString() {
return "Sphere{" +
"radius=" + radius +
'}';
}
#Override
public void describe() {
System.out.println(this);
}
#Override
public Sphere supersize() {
return new Sphere(radius*2);
}
#Override
public double volume() {
return 4*Math.PI*Math.pow(radius, 3)/3;
}
}
Now the generic method that transforms a list
public static <T extends GeometricShape<T>>
List<T> supersize_list(List<T> list) {
List<T> result = new ArrayList<>();
for (T shape : list) {
result.add(shape.supersize());
}
return result;
}

You do not need to return a new Object. For Rectangle for example
#Override
public void supersize()
{
this.width*=2;
this.height*=2;
}
is sufficient

Inheritance casting

I have two class.
class Vector{
........
Vector(int x, int y, int z){...........}
public Vector sum(Vector vc){
Vector result;
...........//all working and store to Vector result.
return result;
}
public Vector subtract(Vector vc){................//codes}
}
class Velocity extends Vector{
Velocity(int x, int y, int z){......}
................
}
class Test{
public static void main(String args){
Velocity v1=new Velocity(14,14,14);
Velocity v2=new Velocity(14,14,14);
Vector result=v1.sum(v2); //here I want to get this result as Velocity
//I don't know how to get it....
}
}
In similar manner I have Acceleration, Force, Momentum, Displacement class which extends Vector class....And all have same problem......besides this

Vector.java:
public interface Vector<T extends Vector> {
public int getX();
public int getY();
public int getZ();
public T sum(T other);
}
BaseVector.java:
public abstract class BaseVector<T extends Vector> implements Vector<T> {
private final int x;
private final int y;
private final int z;
public BaseVector(int x, int y, int z) {
this.x = x;
this.y = y;
this.z = z;
}
protected abstract T createNew(int x, int y, int z);
#Override
public T sum(T other) {
return createNew(x + other.getX(), y + other.getY(), other.getZ());
}
#Override
public int getX() {
return x;
}
#Override
public int getY() {
return y;
}
#Override
public int getZ() {
return z;
}
#Override
public String toString() {
return "BaseVector [x=" + x + ", y=" + y + ", z=" + z + "]";
}
}
Velocity.java:
public class Velocity extends BaseVector<Velocity> {
public Velocity(int x, int y, int z) {
super(x, y, z);
}
#Override
protected Velocity createNew(int x, int y, int z) {
return new Velocity(x, y, z);
}
}
Test.java:
public static void main(String[] args) {
Velocity v1 = new Velocity(14, 14, 14);
Velocity v2 = new Velocity(14, 14, 14);
Velocity result = v1.sum(v2);
System.out.println(result);
}
}

Vector result = ((Velocity)v1).sum(v2);
=========================================================
This will not help, because you defined sum in Vector, returning Vector. To make result a Velocity you would need a sum method returning type Velocity, rather than the one in Vector that returns a Vector.
A better alternative might be to provide a Velocity constructor that takes a Vector
Velocity result = new Velocity(v1.sum(v2));

circle object constructor not defined

I am trying to make class circle extend the Shape class but keep getting a error from JUnit saying the constructor Circle(Point, int) is undefined how would i define the Circle constructor differently from public Circle(Point[] center, int aradius)?
import java.awt.Point;
public abstract class Shape {
private String name;
private Point[] points;
protected Shape(){};
protected Shape(String aName) {
name = aName;
}
public final String getName() {
// TODO Implement method
return name;
}
protected final void setPoints(Point[] thePoints) {
points = thePoints;
}
public final Point[] getPoints() {
// TODO Implement method
return points;
}
public abstract double getPerimeter();
public static double getDistance(Point one, Point two) {
double x = one.getX();
double y = one.getY();
double x2 = two.getX();
double y2 = two.getY();
double x3 = x - x2;
double y3 = y - y2;
double ypow = Math.pow(y3, 2);
double xpow = Math.pow(x3, 2);
double added = xpow + ypow;
double distance = Math.sqrt(added);
return distance;
}
}
Circle.java
import java.awt.Point;
public class Circle extends Shape{
private double radius;
public Circle(Point[] center, int aradius) {
if(radius < 0){
radius = 0;
}
else{
radius = aradius;
}
this.setPoints(center);
}
#Override
public double getPerimeter() {
double perim = 2 * Math.PI * radius;
return perim;
}
public double getRadius(){
return radius;
}
}

Just pass it a single Point, not an array.
public Circle(Point center, int aradius)