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Create a simple math game using java objects

I am trying to create a Simple math game using Java objects. My goal is to create a question class, which contains a method to show a question with random numbers, a method to check the answer, a question constructure.
How can I generate 10 random questions using these objects? With additions, substraction and multiplication questions. And print the how many correct answers, at the end.
I have created my question class and my first method shows a random question using the variables "a" and "b". and store the answer.
My second method check the answer with the user input and print the result. So far when I run my program it only shows the same question over and over again.
This is my Question class
import java.util.*;
public class Question {
private int a;
private int b;
private String Question;
private int correct;
Random rand = new Random();
Scanner input = new Scanner(System.in);
int count = 0;
Question(int c, int d) {
x = rand.nextInt(20);
y = rand.nextInt(20);
}
public void askQuestion() {
if (a > b) {
System.out.println("What is " + a + " - " + b + " ?\n");
correct = a - b;
} else {
System.out.println("What is " + a + " + " + b + " ?\n");
correct = a + b;
}
}
public void Check() {
int response = Integer.parseInt(input.next());
if (response == correct) {
System.out.printf("yes.\n");
count++;
} else {
System.out.printf("No. It is " + correct + ".\n");
}
}
}
my main method looks like this
public class Main {
public static void main(String[] args) {
Question q1 = new Question(1,2);
for (int i = 1; i < 10; i++) {
q1.askQuestion();
q1.check();
}
}
}
In my output it shows the question with two random numbers but it prints the same question over and over again. EX:
What is 13 - 1 ?
12
That is correct.
What is 13 - 1 ?
12
That is correct.
What is 13 - 1 ?
3
Wrong!. The answer is 12.
What is 13 - 1 ?
Eventually I want my output to look like:
What is 4 + 6?
What is 7 - 3?
Any help to fix this? and make this game more interactive? Appreciate it.

Your problem is due to the fact that you are creating one Question object, that generates two random numbers (13 and 1 in your case). You then go through a loop of asking 10 Questions, but you use the same Question object - so you are using the same random numbers every time. To fix this, do the following changes:
In your Question constructor, get rid of the parameters, you do not need them. Assign to variables a and b:
private Question(){
a = rand.nextInt(20);
b = rand.nextInt(20);
}
So every time you create a Question, you will generate two random numbers which you assign to your variables you declared earlier in the code at the top (in your code, a and b are declared, but not used).
Then in your main, change it to the following:
public static void main(String[] args) {
for(int i = 0; i < 10; i++) {
Question q1 = new Question();
q1.askQuestion();
q1.check();
}
System.out.println("Number correct: " + count); //print amount correct, to use this make variable "count" static.
}
The changes are that now you are creating a new Question object every time you go through the loop, and get new random values. Every time it asks a new Question, it will create a new Question object with new random values and overwrite the old ones. It will ask the question 10 times after you give and check the answer, after which the program will output number of correct answers and stop.
Example output for 3 questions:
What is 17 - 15 ?
2
yes.
What is 8 + 11 ?
19
yes.
What is 9 - 0 ?
5
No. It is 9.
Number correct: 2

If you want a way to dynamically ask a question with random numbers and operators, you can create an Operator enum as seen below to handle calculating the result of a left-hand and right-hand value.
Also, the calls to System.out.print should be in the main program as much as possible. Instead, you should return strings from the Question.
All you need to do is pass the two randomly-generated numbers to the Operator enum and ask it to calculate the result.
Exam (main)
package exam;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
public class Exam {
private static int correctCount = 0;
private static List<Question> questions = randomQuestions(10);
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
questions.stream().forEach(question -> ask(question, input));
input.close();
stats();
}
private static void ask(Question question, Scanner input) {
System.out.print(question.askQuestion());
double guess = input.nextDouble();
boolean isCorrect = question.makeGuess(guess);
System.out.println(question.explain(isCorrect));
System.out.println();
correctCount += isCorrect ? 1 : 0;
}
private static void stats() {
double percentage = (correctCount * 1.0d) / questions.size() * 100;
System.out.printf("Correct: %.2f%% (%d/%d)%n", percentage, correctCount, questions.size());
}
private static List<Question> randomQuestions(int count) {
List<Question> questions = new ArrayList<Question>();
while (count --> 0) questions.add(new Question());
return questions;
}
}
Question (class)
package exam;
import java.util.Random;
public class Question {
private static final Random RAND = new Random(System.currentTimeMillis());
private double left;
private double right;
private Operator operator;
public Question(double left, double right, Operator operator) {
this.left = left;
this.right = right;
this.operator = operator;
}
public Question(int max) {
this(randInt(max), randInt(max), Operator.randomOperator());
}
public Question() {
this(10); // Random 0 -> 10
}
public String askQuestion() {
return String.format("What is %s? ", operator.expression(left, right));
}
public String explain(boolean correct) {
return correct ? "Correct" : String.format("Incorrect, it is: %.2f", calculate());
}
public boolean makeGuess(double guess) {
return compareDouble(guess, calculate(), 0.01);
}
private double calculate() {
return operator.calculate(left, right);
}
#Override
public String toString() {
return String.format("%s = %.2f", operator.expression(left, right), calculate());
}
private static boolean compareDouble(double expected, double actual, double threshold) {
return Math.abs(expected - actual) < threshold;
}
private static double randInt(int range) {
return Math.floor(RAND.nextDouble() * range);
}
}
Operator (enum)
package exam;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.Random;
public enum Operator {
ADD("+", (left, right) -> left + right),
SUB("-", (left, right) -> left - right),
MUL("*", (left, right) -> left * right),
DIV("/", (left, right) -> left / right);
private static final Random RAND = new Random(System.currentTimeMillis());
private static final List<Operator> VALUES = Collections.unmodifiableList(Arrays.asList(values()));
private static final int SIZE = VALUES.size();
public static Operator randomOperator() {
return VALUES.get(RAND.nextInt(SIZE));
}
private String symbol;
private Operation operation;
private Operator(String symbol, Operation operation) {
this.symbol = symbol;
this.operation = operation;
}
public double calculate(double left, double right) {
return operation.calculate(left, right);
}
public String expression(double left, double right) {
return String.format("%.2f %s %.2f", left, symbol, right);
}
#Override
public String toString() {
return symbol;
}
}
Operation (interface)
package exam;
public interface Operation {
double calculate(double left, double right);
}

How to use ArrayList in Java?

I am new trying to learn programing and java, I am currently working in a program but I need help starting it, I would really appreciate it if anyone could help me.
I have to Implement a class IrregularPolygon that contains an array list of Point2D.Double objects.
The Point2D.Double class defines a point specified in double precision representing a location in (x, y) coordinate space. For example, Point2D.Double(2.5, 3.1) constructs and initializes a point at coordinates (2.5, 3.1).
I'm going to be Using this declarations as a starting point for my lab work.
import java.awt.geom.*; // for Point2D.Double
import java.util.ArrayList; // for ArrayList
public class IrregularPolygon {
private ArrayList <Point2D.Double> myPolygon;
// constructors
public IrregularPolygon() { }
// public methods
public void add(Point2D.Double aPoint) { }
public double perimeter() { }
public double area() { }
}
I would like some tips on how to Write methods that compute the perimeter and the area of a polygon. To compute the perimeter, and to compute the distance between adjacent points, and total up the distances. The area of a polygon with corners is the absolute value of:

I suggest Math.hypot(point1.getX() - point2.getX(), point1.getY() - point2.getY()) for the distance of to adjacent points. For the perimeter (just as you stated) sum up all distances (don't forget to add the distance from the last to the first point). For the area see How do I calculate the surface area of a 2d polygon?.

I hope you can find this example helpful:
import java.awt.geom.*;
import java.util.ArrayList;
public class IrregularPolygon {
private ArrayList<Point2D.Double> myPolygon;
// constructors
public IrregularPolygon() {
this.myPolygon = new ArrayList<Point2D.Double>();
}
// public methods
public void add(Point2D.Double aPoint) {
this.myPolygon.add(aPoint);
}
public double perimeter() {
// compute perimeter
return 0;
}
public double area() {
// compute area
return 0;
}
#Override
public String toString() {
String result = "IrregularPolygon [";
for (Point2D.Double point : myPolygon) {
result += "|X: " + point.x + ". Y: " + point.y + "|";
}
result += "]";
return result;
}
public static void main(String[] args) {
IrregularPolygon irregularPolygon = new IrregularPolygon();
Point2D.Double point1 = new Point2D.Double(0, 2);
Point2D.Double point2 = new Point2D.Double(2, 4);
Point2D.Double point3 = new Point2D.Double(3, 5);
irregularPolygon.add(point1);
irregularPolygon.add(point2);
irregularPolygon.add(point3);
System.out.println(irregularPolygon.toString());
}
}
You can find in the toString() method how to use the ArrayList in Java, as well as in the add() method, so the implementation of the methods perimeter() and area() just depends on the specs you have. You just need to extrapolate that methods to complete the class.
Hope it helps.
Clemencio Morales Lucas.

this is what i have so far:
import java.awt.geom.*;
import java.util.ArrayList;
public class IrregularPolygon {
private ArrayList <Point2D.Double> myPolygon;
public IrregularPolygon()
{
myPolygon = new ArrayList < Point2D.Double > ();
}
public void add(Point2D.Double aPoint)
{
myPolygon.add(aPoint);
}
public void print()
{
for (Object element : myPolygon)
{
System.out.println(element);
}
}
public double distance(Point2D pt)
{
double distance = 0;
x.distance(y);
return distance;
}
public double perimeter()
{
double distance = 0;
for(int x = 0; x < aPoint; x++){ // cords given in groups might have to / by 2
get.point();
if(myPolygon[] != null){
get.nextPoint();
}
else{
distance += thePoint.distance(nextPoint)
}
}
return distance;
}
public double area()
{
double area = 0;
return area;
}
}
//that's irregular polygon. this is polygon application
import javax.swing.*;
import java.awt.geom.Point2D;
public class PolygonApplication
{
public static void main() {
String userInput;
int pointNumber = 1;
Point2D.Double nextPoint;
IrregularPolygon myPolygon = new IrregularPolygon();
do {
userInput = JOptionPane.showInputDialog("Enter x coordinate for point " + pointNumber);
if (userInput != null) {
double x = Double.parseDouble(userInput);
userInput = JOptionPane.showInputDialog("Enter y coordinate for point " +
pointNumber);
if (userInput != null) {
double y = Double.parseDouble(userInput);
nextPoint = new Point2D.Double(x,y);
myPolygon.add(nextPoint);
pointNumber += 1;
}
}
}
while (userInput != null);
myPolygon.print();
}
}

Setting up the compareTo() method in Java

Please Note:
I created a post earlier that had this question along with several others, but was told that since I was asking so many questions in the same post, it'd be better to break it up into individual questions. So please do not mark this as a duplicate, yes the instructions are the same and yes the same code is being used, but the question itself is different. Thanks.
I'm working on a program with the following instructions:
Write a class named Octagon that extends GeometricObject and implements the Comparable and Cloneable interfaces. Assume that all 8 sides of the octagon are of equal size. The area can be computed using the following formula
area = (2 + 4/square root of 2) * side * side
Write a program (driver) to read in a series of values from a file, display the area and perimeter, create a clone and compare the object and its clone (based on the area). In addition, your program should compare the current object (just read in) with the first object read in. The program ends when a negative number is read from the file.
Here is the code I have so far, This is my GeometricObject class:
public abstract class GeometricObject {
public abstract double getArea();
public abstract double getPerimeter();
}
My Octagon class:
public class Octagon extends GeometricObject implements Comparable<Octagon> {
private double side = 1.0;
protected native Object clone() throws CloneNotSupportedException;
private static int numberOfObjects = 0;
public Octagon() {
}
public Octagon(double side) {
this.side = side;
numberOfObjects++;
}
public double getSide() {
return side;
}
public void setSide(double side) {
this.side = side;
}
public double getArea() {
return (2 + (4 / (Math.sqrt(2))) * side * side);
}
public double getPerimeter() {
return side * 8;
}
public String toString() {
return "Octagon " + numCreated + ": Area: " + getArea() + "\nPerimeter: "
+ getPerimeter() + "\nClone Compare: " + Cloneable + "\nFirst Compare: "
+ comparisson;
}
public int compareTo(Octagon octagon) {
if(getArea() > octagon.getArea())
return 1;
else if(getArea() < octagon.getArea())
return -1;
else
return 0;
}
public interface Cloneable {
}
}
And my Driver or tester class: (this is where I need the most help)
import java.util.*;
import java.io.*;
public class Driver {
public static void main(String[] args) {
int comparisson = compareTo(octagon);
java.io.File file = new java.io.File("prog7.dat");
Scanner fin = new Scanner(file);
while(fin.hasNext()) {
double side = fin.nextDouble();
if(side < 0.0) break;
Octagon first = new Octagon(side);
System.out.println("Octagon 1: " + first);
}
}
}
And here is the file being used to get the input. Each line is one octagon:
5.0
7.5
3.26
0.0
-1.0
I'm having trouble setting up the compareTo() method. I've never used this before and while I've read the documentation and have a general idea of how it works, I'm having trouble figuring out how to implement it to my specific program.
Along these same lines, I know that the compareTo() method returns an integer value of either -1, 0, or 1 based on whether the current object is smaller, larger, or equal to the object it's being compared with. However, as you can see from the example output, rather than displaying this integer value, I"m supposed to display something like "The first is smaller". I'm pretty sure to do this I would need to assign the return value to a variable and then use if statements to determine what should be printed, but I'm having trouble figuring out how and at what point in my code this should be done?

Based on this line of your requirement: In addition, your program should compare the current object (just read in) with the first object read in. Here's some code to do that. Basically this reads Octagons until a negative number is read, and compares each one with the first Octagon read in.
Octagon first = null;
int i = 0;
while(fin.hasNext())
{
double side = fin.nextDouble();
if(side < 0.0)
break;
Octagon oct = new Octagon(side);
System.out.print("Octagon " + i + ": \"" + oct.toString() + "\"");
if (first == null)
first = oct;
else
{
// Here is where we compare the current Octagon to the first one
int comparison = oct.compareTo(first);
if (comparison < 0)
System.out.print(", less than first");
else if (comparison > 0)
System.out.print(", greater than first");
else System.out.print(", equal to first");
}
Octagon first = new Octagon(side);
System.out.println();
}

int compareTo(Object o)
or
int compareTo(String anotherString)
public class Test {
public static void main(String args[]) {
String str1 = "Strings are immutable";
String str2 = "Strings are immutable";
String str3 = "Integers are not immutable";
int result = str1.compareTo( str2 );
System.out.println(result);
result = str2.compareTo( str3 );
System.out.println(result);
result = str3.compareTo( str1 );
System.out.println(result);
}
}
This produces the following result:
0
10
-10
Also you can check -> http://www.javapractices.com/topic/TopicAction.do?Id=10

Java: cannot find symbol

in this class I'm making a catchFish method, it basically returns a random fish from the pond, the fish should be removed from the pond and returned from the method, If there are no fish then null will be returned
this is my code
import java.util.Random;
public class Pond {
private int MAX_FISH = 10;
private Fish[] fish = new Fish[MAX_FISH];
private int numFish;
public Pond (int numFish, Fish[] fish) {
this.numFish = numFish;
this.fish = fish;
}
public int getNumFish() {
return numFish;
}
boolean isFull(){
if (numFish < MAX_FISH) {
return false;
} else {
return true;
}
}
public String toString(){
return "Pond with " + numFish + " fish";
}
public void listFish() {
System.out.println("Pond with " + numFish + " as follows:");
for (int i = 0; i < numFish ; i++) {
Fish f = fish[i];
System.out.println("A " + f.getSize() + " cm " + f.getSpecies());
}
}
public void add(Fish f) {
if (isFull()) {
System.out.println("Sorry, the pond is full!");
} else {
numFish++;
fish[numFish-1] = f;
}
}
public Fish catchAFish() {
if (numFish == 0) {
System.out.println("Sorry, the pond is empty!");
return null;
} else {
Fish f = new Fish();
int r = (int)Math.random()*(numFish-1);
f = fish[r];
if (r == (numFish -1)) {
fish[r] = null;
} else {
fish[r] = fish[numFish-1];
}
numFish--;
return f;
}
}
}
and in catchAFish method the line
Fish f = new Fish(); gives an error:
java:55: cannot find symbol
symbol : constructor Fish()
location: class Fish
and I don't understand what I'm doing wrong?
EDIT:
fish class
public class Fish {
private String species;
private int size;
public Fish(int size, String species) {
this.size = size;
this.species = species;
}
public String toString() {
return " A " + size + " cm " + species;
}
public String getSpecies() {
return species;
}
public int getSize() {
return size;
}
}

Basically...Fish must have a non-empty constructor, requiring you to provide one or parameters when you create an instance of Fish.
Looking at the Fish code, the only constructor you provide is...
public Fish(int size, String species) {
There is no "default" constructor (which would allow you to use new Fish()).
But I'm not convinced that you actually need to create a new instance anyway, as you re-assign it almost immediately.
Fish f = new Fish();
int r = (int)Math.random()*(numFish-1);
// Overridden...
f = fish[r];
Instead, you could simply use...
int r = (int)Math.random()*(numFish-1);
Fish f = fish[r];

Java will create a default constructor, with no arguments, if you don't supply a constructor. So, if you cannot call a no-argument constructor, then you must have created a constructor that does take at least one argument.
Either supply the necessary arguments to call your existing Fish constructor, or create an explicit no-argument Fish constructor.

Since you haven't posted your Fish class I'm going to assume that it's the same as it was in your previous post.
You've defined a constructor for Fish with two parameters. Because you've supplied your own constructor Java will not supply the default no-args constructor. Either define a no-args constructor of your own or use your existing one.

Issue with interfaces in Java

I'm working through an exercise sheet regarding interfaces, generics and abstract classes in Java. No matter what way I seem to code it, the class Exercise1 won't work. The question asked are commented in the code. Any help would be appreciated, I'm not sure if the error is in the Exercise one code or the implementation of the interface in the classes Time and Point.
/*Exercise 2
(a) Write an interface Printable which has a single method put whose intention is to display a string representation of any object whose class implements Printable. Check it by compiling it. */
interface Printable {
public void put(Object o);
}
/*(b) Enhance classes Point and Time from Chapter 2 of the notes to implement Printable. Check them by compiling them. */
class Point implements Printable {
static Scanner sc = new Scanner(System.in);
private double x, y; // coordinates
Point(double x, double y){ // all-args constructor
this.x = x; this.y = y;
}
Point(){}; // no-args constructor (defaults apply)
void get() {
x = sc.nextDouble();
y = sc.nextDouble();
}
public String toString() {
return "(" + x + "," + y + ")";
}
double distance(Point r) { // distance from r
double xdist = x-r.x; double ydist = y-r.y;
return(Math.sqrt(xdist*xdist+ydist*ydist));
}
public void put(Object o) {
if(o==null) return;
Point p = (Point)o;
System.out.println(x + ":" + y);
}
}
class Time implements Order, Printable {
private int hours; // 0..23
private int mins; // 0..59
Time() { }
Time (int hours, int mins) {
this.hours = hours;
this.mins = mins;
}
public boolean lte(Object other) { // Note public
if (other==null) return false;
Time t = (Time) other;
return hours*60+mins<=t.hours*60+t.mins;
}
public void put(Object o) {
if(o==null) return;
Time t = (Time)o;
System.out.printf("%02d:%02d\n", t.hours, t.mins);
}
}
/*(c) Write a static method print which takes an array of objects whose class implements Printable, and prints each element in the array, one element per line. Check it by placing it in an otherwise empty class and compiling it. */
//this is the bit that is giving me grief, I've tried :
public class Exercise1 {
static void print(Printable[] a) {
for(int i = 0; i < a.length ; i++) {
a[i].put(); // put(java.lang.Object) in Printable cannot be applied to () //a[i].put();
}
}
public static void main(String[] args) {
Time[] t = new Time[10];
for(int i = 0; i < t.length; i++) {
t[i] = new Time();
}
print(t);
}
}
public interface Order {
boolean lte (Object obj); // Object for max generality
// is this object less than or equal to obj?
}

You want to print this, not some arbitrary object o.

I think the problem is the interface Printable. It doesn't match the question correctly.
to display a string representation of any object whose class implements Printable
This doesn't mean, that the put() method should have a parameter of type Object.
The object here refers to this, the object which class implements Printable. And the method put() should print out a string representation of this. So in the simplest case you can implement it with the help of toString().
interface Printable {
/**
* Display a string representation of this
*/
void put();
}
class Point implements Printable {
// ...
/**
* returns a string representation of this
*/
public String toString() {
return "(" + x + "," + y + ")";
}
public void put() {
// this is the same as System.out.println(this.toString());
System.out.println(this);
}
}
Then you can call put() for every Printable in your array.

What you want to do is make the interface Printable look something like this:
interface Printable {
public void print(); //The name of the method should be similar to the name of the interface
}
Then your classes will work like this:
public class Time implements Printable {
private int hours, minutes;
public void print() {
System.out.println( hours + ":" + minutes );
}
}
For Exercise 1, you would then call print() for each element of the array.
By the way: There's already an interface similar to Order. It's called Comparable, and it looks like this:
public interface Comparable<T> {
public void compareTo(T other); //Returns -1 if less than, 0 if equal, and 1 if greater than other object.
}
If no parameter T is given, it becomes Object.

you might want your Printable method to be print(Object object), not put.