Reddit's Score

Score.java

import java.time.Instant;
import java.util.Date;
import java.util.concurrent.TimeUnit;

public class Score {

    private final static Date epoch = Date.from(Instant.EPOCH);
    private final Z z = Z.V_50;
    private final int upvotes, downvotes;

    private final long timeDiff;
    private final int score;

    public Score(int upvotes, int downvotes, Date now) {
        this.upvotes = upvotes;
        this.downvotes = downvotes;
        this.timeDiff = TimeUnit.MILLISECONDS.toSeconds(now.getTime() - epoch.getTime());
        this.score = (upvotes - downvotes);
    }

    public double hot() {

        double order = Math.log10(Math.max(Math.abs(this.score), 1));
        double sign = 0;

        if(this.score > 0) {
            sign = 1;
        } else if(score < 0) {
            sign = -1;
        }

        return (sign * order + this.timeDiff / 45000);

    }

    public double controversy() {

        if(this.downvotes <= 0 || this.upvotes <= 0) {
            return 0;
        }

        int magnitude = this.upvotes + downvotes;
        double balance = (upvotes > downvotes ? Double.valueOf(downvotes) / upvotes : Double.valueOf(upvotes) / downvotes);

        return Math.pow(magnitude, balance);

    }

    public double confidence() {

        double n = upvotes + downvotes;

        if(n == 0) {
            return 0;
        }

        double z = this.z.value();
        double p = Double.valueOf(upvotes) / n;

        double left = p + 1 / (2 * n) * Math.pow(z, 2);
        double right = z * Math.sqrt(p * (1 - p) / n + z * z / (4 * n * n));
        double under = 1 +1 / n * z * z;

        return (left - right) / under;

    }

    public enum Z {

        V_50(0.67449D),
        V_75(1.15035D),
        V_80(1.282D),
        V_90(1.64485D),
        V_95(1.95996D),
        V_97(2.17009D),
        V_99(2.57583D),
        V_999(3.29053D);

        private final double z;

        Z(double z) {
            this.z = z;
        }

        public double value() {
            return this.z;
        }

    }

}