(Nov 27, 2016 09:16 PM)Goodies Wrote:  Not much of a java guy to be honest, but does something like this work?

I made this abstract class:

PHP Code


<?php 
public abstract class Maths {
    abstract double sqrt(double value, int sigfigs);
    abstract double abs(double value);
} 


And this interface:

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<?php 
public interface Rounder {
    double round(double value, int places);
} 


And this class called "Stuff" to use both of them.

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<?php 
public class Stuff extends Maths implements Rounder {
    public double round(double value, int places) {
        // truncates a java double into `places` places after the decimal
        long pow = (long)Math.pow(10, places);
        return (long)Math.round(value * pow) / (double)pow;
    }

    @Override
    double abs(double value) {
        // return the absolute value of a number
        return (value >= 0 ? value : -value);
    }

    @Override
    double sqrt(final double value, final int sigfigs) {
        // a simple implementation of the babylonian method of determining the square root of a number
        double prev = -1, curr = sigfigs * 100;
        while(round(prev, sigfigs) != round(curr, sigfigs)) {
            prev = curr;
            curr = (prev + (value / prev)) / 2;
        }
        return round(curr, sigfigs);
    }
} 


And here's an example unit test you can write:

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<?php 
import org.junit.Test;
import org.junit.Assert;

public class Tester {
    @Test
    public void checkRounderRound(){
        final double
                input1 = 123.456, target1 = 123.46, epsilon1 = 0.0,
                input2 = 999999.999999, target2 = 1000000.0, epsilon2 = 0.0,
                input3 = 73737.3737, target3 = 73737.37, epsilon3 = 0.0;

        final int
                sigfigs1 = 2,
                sigfigs2 = 5,
                sigfigs3 = 2;

        Rounder rounder = new Stuff(); // works fine because it implements rounder
        Assert.assertEquals(rounder.round(input1, sigfigs1), target1, epsilon1);
        Assert.assertEquals(rounder.round(input2, sigfigs2), target2, epsilon2);
        Assert.assertEquals(rounder.round(input3, sigfigs3), target3, epsilon3);
    }

    @Test
    public void checkMathsSqrt(){
        final double
                input1 = 100.0, target1 = 10.0, epsilon1 = 0.0,
                input2 = 125348, target2 = 354.04519485512014, epsilon2 = 0.0,
                input3 = 1, target3 = 1, epsilon3 = 0.0;

        final int
                sigfigs1 = 5,
                sigfigs2 = 15,
                sigfigs3 = 5;

        Maths maths = new Stuff(); // works fine because it extends Maths
        Assert.assertEquals(maths.sqrt(input1, sigfigs1), target1, epsilon1);
        Assert.assertEquals(maths.sqrt(input2, sigfigs2), target2, epsilon2);
        Assert.assertEquals(maths.sqrt(input3, sigfigs3), target3, epsilon3);
    }

    @Test
    public void checkMathsAbs(){
        final double
                input1 = 100, target1 = 100, epsilon1 = 0.0,
                input2 = -12345, target2 = 12345, epsilon2 = 0.0,
                input3 = 0, target3 = 0, epsilon3 = 0.0;

        Maths maths = new Stuff();  // works fine because it extends Maths
        Assert.assertEquals(maths.abs(input1), target1, epsilon1);
        Assert.assertEquals(maths.abs(input2), target2, epsilon2);
        Assert.assertEquals(maths.abs(input3), target3, epsilon3);
    }
}