Discountable.java

package com.company;

public interface Discountable {
    public double discountedPrice(double price);
}

Main.java

package com.company;

class Main {
    public static void main(String[] args) {
        PercentageDiscount pd = new PercentageDiscount(20);
        ThresholdDiscount td = new ThresholdDiscount(20, 10);

        double perDiscount = pd.discountedPrice(200);
        double threshold = td.discountedPrice(200);
        System.out.println(perDiscount);
        System.out.println(threshold);
    }
}

PercentageDiscount.java

package com.company;

public class PercentageDiscount implements Discountable{
    private double percentage;

    public PercentageDiscount(double percentage) {
        this.percentage = percentage;
    }

    public double getPercentage() {
        return percentage;
    }

    public void setPercentage(double percentage) {
        this.percentage = percentage;
    }


    @Override
    public double discountedPrice(double price) {
        return (price - (price*percentage)/100);
    }
}

ThresholdDiscount.java

package com.company;

public class ThresholdDiscount implements Discountable {
    private double threshold;
    private double discount;

    public ThresholdDiscount(double threshold, double discount) {
        this.threshold = threshold;
        this.discount = discount;
    }

    public double getThreshold() {
        return threshold;
    }

    public void setThreshold(double threshold) {
        this.threshold = threshold;
    }

    public double getDiscount() {
        return discount;
    }

    public void setDiscount(double discount) {
        this.discount = discount;
    }

    @Override
    public double discountedPrice(double price) {
        return this.discount;
    }
}