Random Equation

package uk.co.lhspro.src;

import java.util.Random;

public class Equation {

    //-----------------------------------------------------[Constant Properties]

    private final static int DEFAULT_RANGE = 10;
    private final static int DEFAULT_NUM_RANGE = 50;
    private final static int EXPRESSION_RANGE = 3;

    private final static int ADDITION = 0;
    private final static int SUBTRACTION = 1;
    private final static int MULTIPLICATION = 2;
    private final static int DIVISION = 3;


    //-----------------------------------------------------[Properties]

    private static Random rand = new Random();

    private int num1;
    private int x;
    private int num2;
    private int y;
    private char expression;
    private float answer;
    private final int range[] = {DEFAULT_RANGE, DEFAULT_NUM_RANGE};

    private char charX = 'x';
    private char charY = 'y';

    //-----------------------------------------------------[Constructors]

    public Equation(int range, int numRange, char x, char y){

        setX(rand.nextInt(range));
        setY(rand.nextInt(range));
        setNum1(rand.nextInt(numRange));
        setNum2(rand.nextInt(numRange));
        setExpression(rand.nextInt(EXPRESSION_RANGE));
        setCharX(x);
        setCharY(y);
        createEquation();
    }

    public Equation(char x, char y){

        this(DEFAULT_RANGE, DEFAULT_NUM_RANGE, x, y);
    }

    public Equation(boolean random){

        this(DEFAULT_RANGE, DEFAULT_NUM_RANGE, (char)(rand.nextInt(25) + 97), (char)(rand.nextInt(25) + 97));

        if(!random){
            System.err.println("Please use default constructor Equation()");
            setCharX('x');
            setCharY('y');
        }

    }

    public Equation(){

        this(DEFAULT_RANGE, DEFAULT_NUM_RANGE, 'x', 'y');
    }

    //-----------------------------------------------------[Private Methods]

    private void createEquation() {

        switch(this.expression){
        case '+':
            this.answer = (num1 * x) + (num2 * y);
            break;
        case '-':
            this.answer =  (num1 * x) - (num2 * y);
            break;
        case '*':
            this.answer = (num1 * x) * (num2 * y);
            break;
        case '/':
            this.answer = (float) (num1 * x) / (num2 * y);
        }
    }

    //-----------------------------------------------------[Getters & Setters]

    /**
     * @return the x
     */
    public int getX() {
        return this.x;
    }

    /**
     * @param x the x to set
     */
    private void setX(int x) {
        this.x = x;
    }

    /**
     * @return the y
     */
    public int getY() {
        return this.y;
    }

    /**
     * @param y the y to set
     */
    private void setY(int y) {
        this.y = y;
    }

    /**
     * @return the expression
     */
    public char getExpression() {
        return this.expression;
    }

    /**
     * @param num between 0 and 3 to generate an expression for the equation
     */
    private void setExpression(int num) {

        switch(num){

        case ADDITION:
            this.expression = '+';
            break;
        case SUBTRACTION:
            this.expression = '-';
            break;
        case MULTIPLICATION:
            this.expression = '*';
            break;
        case DIVISION:
            this.expression = '/';
            break;
        default:
            System.err.println("Not valid int to generate Expression");;
        }
    }

    /**
     * @param exp to set the expression
     */
    private void setExpression(char exp) {

        if(exp == '+' || exp == '-' || exp == '*' || exp == '/'){
            this.expression = exp;
        } else {
            System.err.println("Expression is invalid or not yet implemented.");
        }
    }

    /**
     * @return the charX
     */
    public char getCharX() {
        return this.charX;
    }

    /**
     * @param charX the charX to set
     */
    public void setCharX(char charX) {
        this.charX = charX;
    }

    /**
     * @return the charY
     */
    public char getCharY() {
        return this.charY;
    }

    /**
     * @param charY the charY to set
     */
    public void setCharY(char charY) {
        this.charY = charY;
    }


    /**
     * @return the num1
     */
    public int getNum1() {
        return this.num1;
    }


    /**
     * @param num1 the num1 to set
     */
    public void setNum1(int num1) {
        this.num1 = num1;
    }


    /**
     * @return the num2
     */
    public int getNum2() {
        return this.num2;
    }


    /**
     * @param num2 the num2 to set
     */
    public void setNum2(int num2) {
        this.num2 = num2;
    }

    public int getRange(){
        return this.range[0];
    }

    public int getNumRange(){
        return this.range[1];
    }

    @Override
    public String toString(){

        return (Integer.toString(this.num1) + this.charX
                + ' ' + this.expression + ' '
                + Integer.toString(this.num2) + this.charY
                + " = " + this.answer);
    }

    //-----------------------------------------------------[Test Driver]

    public static void main(String[] args){
        Equation eq = new Equation();
        System.out.println( "Num1: " + eq.getNum1()
                        +   "\nx: " + eq.getX()
                        +   "\nExpression: " + eq.getExpression()
                        +   "\nNum2: " + eq.getNum2()
                        +   "\ny: " + eq.getY()
                        +   "\nChar x: " + eq.getCharX()
                        +   "\nChar y: " + eq.getCharY()
                        +   "\nRange: " + eq.getRange()
                        +   "\nNum Range: " + eq.getNumRange()
                        );
        System.out.println(eq);
    }
}