Arbitrary? Number Modification

Question

A little background info: I'm trying to program an understanding of units of time, and be able to convert milliseconds to seconds to minutes to all the rest and back again.
The code below successfully converts the current time from milliseconds to seconds to milliseconds (most of the time) and prints the value after each step. My problem is that it sometimes adds a little bit to the end, and an example of the malformed output then one of the expected output are at the end of this post.
package jesdisciple.util.units;
public final class Type {
    public static final Type TIME = new Type();
package jesdisciple.util;
public final class JesAmount {
    private final JesUnit u;
    private final double v;
    public JesAmount(double value, JesUnit unit) {
        v = value;
        u = unit;
    public final boolean equals(JesAmount amount){
        return v == amount.v && u.equals(amount.u);
    public final JesAmount convertTo(JesUnit unit){
        if(!unit.type.equals(u.type)) throw new IllegalArgumentException("Cannot convert to a dissimilar unit type.");
        return new JesAmount(v * (u.factor / unit.factor), unit);
package jesdisciple.util;
import jesdisciple.util.units.*;
public final class JesUnit {
    public static final int MAXIMUM_PRECISION = 3; // I'm unsure what this value should be.
    public static final JesUnit SECOND = new JesUnit(Type.TIME, " s", -1);
     * Identifies what type of quantity this unit measures.
    public final Type type;
     * Describes what {@link JesAmount#toString() JesAmount.toString()} should append to the value,
     * such as " m" (for meters) or "$" (for dollars).
    public final String notation;
     * Describes how many digits after the decimal point should be retained.
    public final int precision;
     * Describes the numeric relation between the {@link #bases base unit(s)}
     * and this unit. (I.e., 12 is the factor of a foot to an inch, 1000 is
     * the factor of a kilometer to a meter, and 0.001 is the factor of a gram
     * to a kilogram.)
    public final double factor;
     * Describes where to put the notation. The default value is {@code true},
     * which renders the notation after the value, so {@code true} need not be
     * specified in any constructor. {@code false}, on the other hand, must be
     * specified.
    public final boolean after;
     * Holds representation(s) for the one or two units from which this is
     * derived.
    public final JesUnit[] bases = new JesUnit[2];
    private JesUnit(Type t, String notation, int precision, boolean after){
        this.type = t;
        this.factor = 1;
        this.notation = notation;
        this.precision = precision == -1 ? MAXIMUM_PRECISION : precision;
        this.after = after;
    private JesUnit(Type t, String notation, int precision){
        this(t, notation, precision, true);
    public JesUnit(JesUnit u, double factor, String notation, int precision, boolean after){
        this.type = u.type;
        this.notation = notation;
        this.precision = precision == -1 ? MAXIMUM_PRECISION : precision;
        this.bases[0] = u.getBase();
        this.factor = factor * (u.isBase() ? 1 : u.factor);
        this.after = after;
    public JesUnit(JesUnit u, double factor, String notation, int precision){
        this(u, factor, notation, precision, true);
    public final JesUnit getBase(){
        if(bases[0] == null){
            if(bases[1] == null) return this;
            else return bases[1].getBase();
        }else{
            if(bases[1] == null) return bases[0].getBase();
            else return this;
    public final boolean isBase(){
        return (bases[0] == null) == (bases[1] == null);
package jesdisciple.lang;
import jesdisciple.util.*;
public class JesMain {
    public static void main(String[] args) {
        JesUnit millisecond = new JesUnit(JesUnit.SECOND, 0.001, " ms", 0);
        JesAmount timeMillis = new JesAmount(System.currentTimeMillis(), millisecond);
System.out.println(timeMillis);
        JesAmount time = timeMillis.convertTo(JesUnit.SECOND);
System.out.println(time);
        timeMillis = time.convertTo(millisecond);
System.out.println(timeMillis);
init:
deps-jar:
compile:
run:
1.183856340906E12 ms
1.1838563409060001E9 s
1.1838563409060002E12 ms
BUILD SUCCESSFUL (total time: 0 seconds)Here is the expected and usual output:init:
deps-jar:
compile:
run:
1.183856340906E12 ms
1.183856340906E9 s
1.183856340906E12 ms
BUILD SUCCESSFUL (total time: 0 seconds)Can this be fixed somehow, or is it a bug in Java itself?

Answer 1

How do you suggest that I fix it? According to http://java.sun.com/developer/JDCTechTips/2003/tt0204.html#2,
There are several ways to fix the equality testing problem illustrated above. You could check that d and val2 are close in value rather than exactly equal. Or you could use the BigDecimal class, and opt out of floating-point arithmetic entirely.
Ironically, I tried BigDecimal earlier and got stranger numbers than shown above. JesAmount should have this method:    public final String toString(){
        String out = u.notation;
        out = u.after ? v + out : out + v;
        return out;
    }, but I deleted it as irrelevant earlier, and this algorithm instead of the other:    public final JesAmount convertTo(JesUnit unit){
        if(!unit.type.equals(u.type)) throw new IllegalArgumentException("Cannot convert to a dissimilar unit type.");
        return new JesAmount(v.multiply(new BigDecimal(u.factor).divide(new BigDecimal(unit.factor))), unit);
    }, and this constructor:    public JesAmount(BigDecimal value, JesUnit unit) {
        v = value;
        u = unit;
    }, and JesMain should have this one:    public static void main(String[] args) {
        JesUnit millisecond = new JesUnit(JesUnit.SECOND, 0.001, " ms", 0);
        JesAmount timeMillis = new JesAmount(new BigDecimal(System.currentTimeMillis()), millisecond);
System.out.println(timeMillis);
        JesAmount time = timeMillis.convertTo(JesUnit.SECOND);
System.out.println(time);
        timeMillis = time.convertTo(millisecond);
System.out.println(timeMillis);
    }, both classes now importing java.math.*. Here is the output from that:init:
deps-jar:
Compiling 1 source file to C:\Program Files\netbeans-5.5.1\projects\Jesdisciple\build\classes
compile:
run:
1183897140296 ms
1183897140.296000024644809948959345291541467304341495037078857421875000 s
Exception in thread "main" java.lang.ArithmeticException: Non-terminating decimal expansion; no exact representable decimal result.
        at java.math.BigDecimal.divide(BigDecimal.java:1514)
        at jesdisciple.util.JesAmount.convertTo(JesAmount.java:49)
        at jesdisciple.lang.JesMain.main(JesMain.java:33)
Java Result: 1
BUILD SUCCESSFUL (total time: 5 seconds)Message was edited by:
Jesdisciple