Develop Reference

Getting run time input in Abstract class in Java

Problem Statement is "To develop a Java Program to create an abstract class named Shape that contains two integers and an empty method named printArea(). Provide three classes named Rectangle, Triangle and Circle such that each one of the classes extends the class Shape. Each one of the classes contains only the method printArea() that prints the area of the given shape."
In this program, I want to get the two integer values contained by the abstract class Shape, from the user (run time) instead of compile time.
This is my code
abstract class Shape
{
abstract void Printarea();
int a=10,b=2;;
}
class Rectangle extends Shape
{
void Printarea()
{
System.out.println("area of rectangle is "+(a*b));
}
}
class Triangle extends Shape
{
void Printarea()
{
System.out.println("area of triangle is "+(0.5*a*b));
}
}
class Circle extends Shape
{
void Printarea()
{
System.out.println("area of circle is "+(3.14*a*a));
}
}
class Main
{
public static void main(String []args)
{
Shape=b;
b=new Circle();
b.Printarea();
b=new Rectangle();
b.Printarea();
b=new Triangle();
b.Printarea();
}
}

Add Setter and getter method for variables a,b ;
here's my code
package com.docker.container.controllers;
/**
* #author atwa Jul 29, 2018
*/
public abstract class Shape {
abstract void Printarea();
int a = 10, b = 2;
/**
* #return the a
*/
public int getA() {
return a;
}
/**
* #param a
* the a to set
*/
public void setA(int a) {
this.a = a;
}
/**
* #return the b
*/
public int getB() {
return b;
}
/**
* #param b
* the b to set
*/
public void setB(int b) {
this.b = b;
}
static public class Rectangle extends Shape {
void Printarea()
{
System.out.println("area of rectangle is " + (a * b));
}
}
static class Triangle extends Shape
{
void Printarea()
{
System.out.println("area of triangle is " + (0.5 * a * b));
}
}
static class Circle extends Shape
{
void Printarea()
{
System.out.println("area of circle is " + (3.14 * a * a));
}
}
// area of circle is 314.0
// area of rectangle is 20
// area of triangle is 10.0
public static void main(String[] args)
{
Shape b = new Circle();
b.setA(5);
b.setB(5);
b.Printarea();
b = new Rectangle();
b.Printarea();
b = new Triangle();
b.Printarea();
}
}

you can use Scanner class
like this
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
int i = scan.nextInt();
}

Some quick code but works as expected and would give you idea:
import java.util.Scanner;
abstract class Shape {
int a = 10, b = 2;
Shape(int a, int b){
this.a=a;
this.b=b;
}
abstract void Printarea();
}
class Rectangle extends Shape {
Rectangle(int a, int b) {
super(a, b);
}
void Printarea() {
System.out.println("area of rectangle is " + (a * b));
}
}
class Triangle extends Shape {
Triangle(int a, int b) {
super(a, b);
}
void Printarea(){
System.out.println("area of triangle is " + (0.5 * a * b));
}
}
class Circle extends Shape {
Circle(int a, int b) {
super(a, b);
}
void Printarea() {
System.out.println("area of circle is " + (3.14 * a * a));
}
}
class Z {
public static void main(String[] args){
Shape shape=null;
String input;
int width, height;
while (true) {
Scanner scanner = new Scanner(System.in);
System.out.println("which shape? circle/rectangle/triangle (write any other thing for quitting): ");
input = scanner.nextLine();
if(!"circle".equalsIgnoreCase(input) && !"rectangle".equalsIgnoreCase(input) && !"triangle".equalsIgnoreCase(input) ){
System.exit(0);
}
System.out.println("height: ");
height = scanner.nextInt();
System.out.println("width: ");
width = scanner.nextInt();
if("circle".equalsIgnoreCase(input)){
shape=new Circle(width, height);
}
else if("rectangle".equalsIgnoreCase(input)){
shape=new Rectangle(width, height);
}
else{ // == triangle
shape=new Triangle(width, height);
}
shape.Printarea();
}
}
}

Try with this:
public class Main {
public static void main(String[] args) {
Shape b;
Scanner in = new Scanner(System.in);
int x = in.nextInt();
int y = in.nextInt();
b = new Circle(x, y);
b.Printarea();
b = new Rectangle(x, y);
b.Printarea();
b = new Triangle(x, y);
b.Printarea();
}
private static int Abs(int a) {
return a < 0 ? -a : a;
}
}
abstract class Shape {
int a, b;
public Shape(int a, int b) {
this.a = a;
this.b = b;
}
abstract void Printarea();
}
class Rectangle extends Shape {
public Rectangle(int a, int b) {
super(a, b);
}
void Printarea()
{
System.out.println("area of rectangle is " + (a * b));
}
}
class Triangle extends Shape {
public Triangle(int a, int b) {
super(a, b);
}
void Printarea()
{
System.out.println("area of triangle is " + (0.5 * a * b));
}
}

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

Java - How to print methods of a certain object from ArrayList?

Basically I have an ArrayList of Objects. There are different types of objects, such as Triangles, Rectangles, and Spheres. Each object has its own method, such as getArea, getPerimeter, and getVolume. These methods are different for each object. How do I iterate through the ArrayList to print out all of the methods of each object?
So say I start with a Triangle. How do I print its getArea and getPerimeter methods with a for loop and a switch block / if statement?

You can use a simple for loop to iterate over your ArrayList, and then call the toString() method of the object:
for (int = 0; i < arrayList.size(); i++)
{
System.out.println(arrayList.get(i).toString());
}
To override the toString method of your class, just add the method, pretty simple:
class Rectangle
{
//Member variables
int width, height; //Example
//Member functions
getArea { ... }
//toString
public String toString()
{
return String.valueOf(getArea());
}
}

for(int i=0; i<listOfObjects.length; i++) {
Object obj = listOfObjects[i];
if (obj instanceof Triangle) {
Triangle t = (Triangle) obj;
t.getArea();
} else if (obj instanceof Rectangle) {
Rectangle r = (Rectangle) obj;
r.getPerimeter();
} else {
Sphere s = (Sphere) obj;
s.getSomeOtherThing();
}
}

Check this. An alternative to instanceof operator
ArrayList arr=new ArrayList();
arr.add(new Traingle());
arr.add(new Rectangle());
arr.add(new Sphere());
for(Object obj:arr){
int value=0;
switch (obj.getClass().getSimpleName()){
case "Rectangle":
value=((Rectangle) obj).getPerimeter();
break;
case "Traingle":
value=((Traingle) obj).getArea();
break;
case "Sphere":
value=((Sphere) obj).getVolume();
break;
default:
break;
}
System.out.println("Object "+obj.getClass().getSimpleName()+":"+value);
}

Why not use an Interface?
package com.spiderman;
public interface Shape {
public void getArea();
public void getPerimeter();
public void getVolume();
}
package com.spiderman;
public class Rectangle implements Shape {
#Override
public void getArea() {
System.out.println("area of Rectangle");
}
#Override
public void getPerimeter() {
System.out.println("perimiter of Rectangle");
}
#Override
public void getVolume() {
System.out.println("volume of Rectangle");
}
}
package com.spiderman;
public class Triangle implements Shape {
#Override
public void getArea() {
System.out.println("area of Triangle");
}
#Override
public void getPerimeter() {
System.out.println("perimiter of Triangle");
}
#Override
public void getVolume() {
System.out.println("volume of Triangle");
}
}
package com.prash;
public class Sphere implements Shape {
#Override
public void getArea() {
System.out.println("area of Sphere");
}
#Override
public void getPerimeter() {
System.out.println("perimiter of Sphere");
}
#Override
public void getVolume() {
System.out.println("volume of Sphere");
}
}
package com.spiderman;
import java.util.ArrayList;
import java.util.List;
public class Main {
public static void main(String[] args) {
List<Shape> list = new ArrayList<Shape>();
list.add(new Rectangle());
list.add(new Triangle());
list.add(new Sphere());
for (int i = 0; i < list.size(); i++) {
Shape shape = list.get(i);
shape.getArea();
shape.getPerimeter();
shape.getVolume();
System.out.println("------------------");
}
}
}
OUTPUT:
area of Rectangle
perimiter of Rectangle
volume of Rectangle
area of Triangle
perimiter of Triangle
volume of Triangle
area of Sphere
perimiter of Sphere
volume of Sphere

How to create an object from data in a file and assign it to an array?

I need to take information from a file and create them into objects and put them into an array so I can compare the areas of the objects and list in the array which object has the largest area and its location in the array.
I'm confused on how I take the information from the file and create each one into a object (circle or rectangle) and then assign that object into an array after it has been created. I think my other classes are fine, I'm just stuck on finishing the driver.
Normally, I would do something like Circle c1 = new Circle(); to create a new object, but how do I do that from a file with predefined information and assign it to an array?
Data:
“CIRCLE”, 1, “blue”, true
“RECTANGLE”, 1, 2, “blue”, true
“RECTANGLE”, 10, 2, “red”, true
“CIRCLE”, 2, “green”
“RECTANGLE”
“CIRCLE”
Driver:
import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.Scanner;
public class Driver {
public static void main(String[] args) throws FileNotFoundException {
Scanner input = new Scanner(new File("C:/Users/Charles/Desktop/GeometricObjectsData.txt"));
ArrayList<GeometricObject> list = new ArrayList<GeometricObject>();
while (input.hasNext()) {
String line = input.nextLine();
System.out.println(line);
}
}
}
GeometricObject:
public abstract class GeometricObject {
//class variables
private String color;
private boolean filled;
//constructors
public GeometricObject() {
super();
color = "white";
filled = false;
}
public GeometricObject(String color, boolean filled) {
super();
this.color = color;
this.filled = filled;
}
//mutators
public String getColor() {
return color;
}
public void setColor(String color) {
this.color = color;
}
public boolean isFilled() {
return filled;
}
public void setFilled(boolean filled) {
this.filled = filled;
}
//user-defined methods
public abstract double getArea();
public abstract double getPerimeter();
#Override
public String toString() {
return super.toString() + " \tColor=" + this.getColor() + " \tFilled=" + this.isFilled();
}
}
Circle:
public class Circle extends GeometricObject {
//class variables
private double radius;
//constructors
public Circle() {
super();
radius = 1;
}
public Circle(double radius, String color, boolean filled) {
super(color, filled);
this.radius = radius;
}
//mutators
public double getRadius() {
return radius;
}
public void setRadius(double radius) {
this.radius = radius;
}
//user-defined methods
#Override
public double getArea() {
//area of a circle
return (radius * radius * Math.PI);
}
#Override
public double getPerimeter() {
//perimeter of a circle
return (2 * radius * Math.PI);
}
#Override
public String toString() {
return super.toString() + "\nCircle: Radius=" + this.getRadius();
}
}
Rectangle:
public class Rectangle extends GeometricObject {
//class variables
private double height;
private double width;
//constructors
public Rectangle() {
super();
height = 1;
width = 1;
}
public Rectangle(double height, double width, String color, boolean filled) {
super(color,filled);
this.height = height;
this.width = width;
}
//mutators
public double getHeight() {
return height;
}
public void setHeight(double height) {
this.height = height;
}
public double getWidth() {
return width;
}
public void setWidth(double width) {
this.width = width;
}
//user-defined methods
#Override
public String toString() {
return super.toString() + "\nRectangle: Height=" + this.height + "\tWidth=" + this.width;
}
#Override
public double getArea() {
return (height * width);
}
#Override
public double getPerimeter() {
return (2 * height + 2 * width);
}
}

In your text file, you have special quotes around your shape items. This will make your life more difficult, so you should change that, if possible
Example of how to make objects (from your main method):
while (input.hasNext()) {
String line = input.nextLine();
System.out.println(line);
String[] parts = line.split(",");
if (parts[0].indexOf("Circle") != -1) {
Circle c = new Circle();
// ... parse the rest of the attributes to set up your circle
} else if ... // fill in the other shape cases
}

What's wrong with my getArea method?

This is a homework problem. There are a few other java files involved. Note that shapes.Rectangle and shapes.Oval contain a getArea method. I'm having a maddening time trying to figure this out any help is appreciated.
package model;
import java.awt.Color;
import java.awt.Container;
import shapes.Line;
import shapes.Oval;
import shapes.Rectangle;
import shapes.Shape;
import shapes.Triangle;
import interfaces.ComparableShape;
import interfaces.Resettable;
public class Model implements Resettable,ComparableShape {
private Container container;
private String message;
private String action = DRAW;
private boolean fill = false;
private String currentShapeType;
private Shape currentShape;
private Color fillColor = Color.gray;
public Color lineColor;
public final static String DRAW = "Draw";
public final static String MOVE = "Move";
public final static String REMOVE = "Remove";
public final static String RESIZE = "Resize";
public final static String FILL = "Fill";
public final static String CHANGE = "Change";
public final static String RECTANGLE = "Rectangle";
public final static String OVAL = "Oval";
public final static String LINE = "Line";
public final static String TRIANGLE = "Triangle";
public static String[] selections = {"Rectangle", "Oval", "Line", "Triangle"};
//project 9 begin
public Shape[] myShapes = new Shape[2];
//project 9 stop
public Shape createShape() {
if(currentShapeType == RECTANGLE){
currentShape = new Rectangle(0, 0, 0, 0, lineColor, fillColor, fill);
}
if(currentShapeType == OVAL) {
currentShape = new Oval(0,0,0,0, lineColor, fillColor, fill);
}
if(currentShapeType == LINE) {
currentShape = new Line(0,0,0,0, lineColor, fillColor, fill);
}
if(currentShapeType == TRIANGLE) {
currentShape = new Triangle(0,0,0,0, lineColor, fillColor, fill);
}
//project 9 start
if(myShapes[0] == null) {
myShapes[0]=currentShape;
}
else {
myShapes[1]=currentShape;
}
//project 9 stop
return currentShape;
}
public Shape getCurrentShape() {
return currentShape;
}
//project 9 begin
public Shape[] getMyShapearray() {
return myShapes;
}
//project 9 end
public String getCurrentShapeType(){
return currentShapeType;
}
public void setCurrentShapeType(String shapeType){
currentShapeType = shapeType;
}
public Model(Container container) {
this.container = container;
}
public void repaint() {
container.repaint();
}
public String getAction() {
return action;
}
public void setAction(String action) {
this.action = action;
}
public boolean isFill() {
return fill;
}
public void setFill(boolean fill) {
this.fill = fill;
}
public void setMessage(String msg) {
this.message = msg;
}
public String getMessage() {
return this.message;
}
public Color getLineColor() {
return this.lineColor;
}
public void setLineColor(Color c) {
this.lineColor = c;
}
public String toString() {
return "Model:\n\tAction: " + action + "\n\tFill: " + fill + "\n\tArea: " ;
}
public void resetComponents() {
action = DRAW;
currentShape = null;
myShapes = null;
if (container instanceof Resettable) {
((Resettable) container).resetComponents();
}
}
//Add a method to your model called compareShapes(),
//which will return either 0, 1, or 2--1 if the area of the first Shape is bigger than the second,
//2 if it is smaller, and 0 if the two Shapes are the same size.
//Create an interface named ComparableShape that will be used by the shape objects.
//The interface should require implementing classes to have a
//method getArea() capable of returning the area of the object. Obviously, only closed shapes can do this.
//The instanceof operator will be handy here.
public int getArea() {
return getWidth()*getHeight();
}
private int getHeight() {
///what goes here?!
return 0;
}
private int getWidth() {
//what goes here?!
return 0;
}
public int compareShapes(ComparableShape b) {
ComparableShape oneToCompare = null;
if (b instanceof ComparableShape) {
oneToCompare = (ComparableShape)b;
if (getArea() < oneToCompare.getArea()) return 2; // this one is smaller
if (getArea() > oneToCompare.getArea()) return 1; // this one is larger
return 0;
}
return 0;
}
}

Your getArea() should have something like this:-
If currentShapeType is not a LINE (since a line is not closed shape), then calculate and return area of currentShape based on the currentShapeType.

The area of a rectangle is length*width. It's different for the other shapes though. So for a rectangle you need access to its length and width. For a circle you would need its radius. The area of a circle is piR^2.
As someone mentioned below, for an ellipse:
The area of an ellipse is pi*a*b, where a and b are half the length of the major and minor axes. The area of a circle could be written as pi*r*r or pi*r^2 since a and b would be equal.