Added the ability to restrict conversion to customary->metric.

5 files changed, 333 insertions, 199 deletions

diff --git a/src/org/unitConverter/converterGUI/SearchBoxList.java b/src/org/unitConverter/converterGUI/SearchBoxList.java
index 1995466..10ef589 100644
--- a/src/org/unitConverter/converterGUI/SearchBoxList.java
+++ b/src/org/unitConverter/converterGUI/SearchBoxList.java
@@ -36,13 +36,13 @@ import javax.swing.JTextField;
  * @since v0.2.0
  */
 final class SearchBoxList extends JPanel {
-
+	
 	/**
 	 * @since 2019-04-13
 	 * @since v0.2.0
 	 */
 	private static final long serialVersionUID = 6226930279415983433L;
-
+	
 	/**
 	 * The text to place in an empty search box.
 	 * 
@@ -50,7 +50,7 @@ final class SearchBoxList extends JPanel {
 	 * @since v0.2.0
 	 */
 	private static final String EMPTY_TEXT = "Search...";
-
+	
 	/**
 	 * The color to use for an empty foreground.
 	 * 
@@ -58,94 +58,92 @@ final class SearchBoxList extends JPanel {
 	 * @since v0.2.0
 	 */
 	private static final Color EMPTY_FOREGROUND = new Color(192, 192, 192);
-
+	
 	// the components
 	private final Collection<String> itemsToFilter;
 	private final DelegateListModel<String> listModel;
 	private final JTextField searchBox;
 	private final JList<String> searchItems;
-
+	
 	private boolean searchBoxEmpty = true;
-
-	// I need to do this because, for some reason, Swing is auto-focusing my search box without triggering a focus
+	
+	// I need to do this because, for some reason, Swing is auto-focusing my
+	// search box without triggering a focus
 	// event.
 	private boolean searchBoxFocused = false;
-
+	
 	private Predicate<String> customSearchFilter = o -> true;
 	private final Comparator<String> defaultOrdering;
 	private final boolean caseSensitive;
-
+	
 	/**
 	 * Creates the {@code SearchBoxList}.
 	 * 
-	 * @param itemsToFilter
-	 *            items to put in the list
+	 * @param itemsToFilter items to put in the list
 	 * @since 2019-04-14
 	 */
 	public SearchBoxList(final Collection<String> itemsToFilter) {
 		this(itemsToFilter, null, false);
 	}
-
+	
 	/**
 	 * Creates the {@code SearchBoxList}.
 	 * 
-	 * @param itemsToFilter
-	 *            items to put in the list
-	 * @param defaultOrdering
-	 *            default ordering of items after filtration (null=Comparable)
-	 * @param caseSensitive
-	 *            whether or not the filtration is case-sensitive
+	 * @param itemsToFilter   items to put in the list
+	 * @param defaultOrdering default ordering of items after filtration
+	 *                        (null=Comparable)
+	 * @param caseSensitive   whether or not the filtration is case-sensitive
 	 * 
 	 * @since 2019-04-13
 	 * @since v0.2.0
 	 */
-	public SearchBoxList(final Collection<String> itemsToFilter, final Comparator<String> defaultOrdering,
+	public SearchBoxList(final Collection<String> itemsToFilter,
+			final Comparator<String> defaultOrdering,
 			final boolean caseSensitive) {
 		super(new BorderLayout(), true);
 		this.itemsToFilter = itemsToFilter;
 		this.defaultOrdering = defaultOrdering;
 		this.caseSensitive = caseSensitive;
-
+		
 		// create the components
 		this.listModel = new DelegateListModel<>(new ArrayList<>(itemsToFilter));
 		this.searchItems = new JList<>(this.listModel);
-
+		
 		this.searchBox = new JTextField(EMPTY_TEXT);
 		this.searchBox.setForeground(EMPTY_FOREGROUND);
-
+		
 		// add them to the panel
 		this.add(this.searchBox, BorderLayout.PAGE_START);
 		this.add(new JScrollPane(this.searchItems), BorderLayout.CENTER);
-
+		
 		// set up the search box
 		this.searchBox.addFocusListener(new FocusListener() {
 			@Override
 			public void focusGained(final FocusEvent e) {
 				SearchBoxList.this.searchBoxFocusGained(e);
 			}
-
+			
 			@Override
 			public void focusLost(final FocusEvent e) {
 				SearchBoxList.this.searchBoxFocusLost(e);
 			}
 		});
-
+		
 		this.searchBox.addCaretListener(e -> this.searchBoxTextChanged());
 		this.searchBoxEmpty = true;
 	}
-
+	
 	/**
 	 * Adds an additional filter for searching.
 	 * 
-	 * @param filter
-	 *            filter to add.
+	 * @param filter filter to add.
 	 * @since 2019-04-13
 	 * @since v0.2.0
 	 */
 	public void addSearchFilter(final Predicate<String> filter) {
 		this.customSearchFilter = this.customSearchFilter.and(filter);
 	}
-
+	
 	/**
 	 * Resets the search filter.
 	 * 
@@ -155,7 +153,7 @@ final class SearchBoxList extends JPanel {
 	public void clearSearchFilters() {
 		this.customSearchFilter = o -> true;
 	}
-
+	
 	/**
 	 * @return this component's search box component
 	 * @since 2019-04-14
@@ -164,11 +162,11 @@ final class SearchBoxList extends JPanel {
 	public final JTextField getSearchBox() {
 		return this.searchBox;
 	}
-
+	
 	/**
-	 * @param searchText
-	 *            text to search for
-	 * @return a filter that filters out that text, based on this list's case sensitive setting
+	 * @param searchText text to search for
+	 * @return a filter that filters out that text, based on this list's case
+	 *         sensitive setting
 	 * @since 2019-04-14
 	 * @since v0.2.0
 	 */
@@ -176,9 +174,10 @@ final class SearchBoxList extends JPanel {
 		if (this.caseSensitive)
 			return string -> string.contains(searchText);
 		else
-			return string -> string.toLowerCase().contains(searchText.toLowerCase());
+			return string -> string.toLowerCase()
+					.contains(searchText.toLowerCase());
 	}
-
+	
 	/**
 	 * @return this component's list component
 	 * @since 2019-04-14
@@ -187,7 +186,7 @@ final class SearchBoxList extends JPanel {
 	public final JList<String> getSearchList() {
 		return this.searchItems;
 	}
-
+	
 	/**
 	 * @return index selected in item list
 	 * @since 2019-04-14
@@ -196,7 +195,7 @@ final class SearchBoxList extends JPanel {
 	public int getSelectedIndex() {
 		return this.searchItems.getSelectedIndex();
 	}
-
+	
 	/**
 	 * @return value selected in item list
 	 * @since 2019-04-13
@@ -205,7 +204,7 @@ final class SearchBoxList extends JPanel {
 	public String getSelectedValue() {
 		return this.searchItems.getSelectedValue();
 	}
-
+	
 	/**
 	 * Re-applies the filters.
 	 * 
@@ -213,29 +212,30 @@ final class SearchBoxList extends JPanel {
 	 * @since v0.2.0
 	 */
 	public void reapplyFilter() {
-		final String searchText = this.searchBoxEmpty ? "" : this.searchBox.getText();
-		final FilterComparator comparator = new FilterComparator(searchText, this.defaultOrdering, this.caseSensitive);
+		final String searchText = this.searchBoxEmpty ? ""
+				: this.searchBox.getText();
+		final FilterComparator comparator = new FilterComparator(searchText,
+				this.defaultOrdering, this.caseSensitive);
 		final Predicate<String> searchFilter = this.getSearchFilter(searchText);
-
+		
 		this.listModel.clear();
 		this.itemsToFilter.forEach(string -> {
 			if (searchFilter.test(string)) {
 				this.listModel.add(string);
 			}
 		});
-
+		
 		// applies the custom filters
 		this.listModel.removeIf(this.customSearchFilter.negate());
-
+		
 		// sorts the remaining items
 		this.listModel.sort(comparator);
 	}
-
+	
 	/**
 	 * Runs whenever the search box gains focus.
 	 * 
-	 * @param e
-	 *            focus event
+	 * @param e focus event
 	 * @since 2019-04-13
 	 * @since v0.2.0
 	 */
@@ -246,12 +246,11 @@ final class SearchBoxList extends JPanel {
 			this.searchBox.setForeground(Color.BLACK);
 		}
 	}
-
+	
 	/**
 	 * Runs whenever the search box loses focus.
 	 * 
-	 * @param e
-	 *            focus event
+	 * @param e focus event
 	 * @since 2019-04-13
 	 * @since v0.2.0
 	 */
@@ -262,7 +261,7 @@ final class SearchBoxList extends JPanel {
 			this.searchBox.setForeground(EMPTY_FOREGROUND);
 		}
 	}
-
+	
 	/**
 	 * Runs whenever the text in the search box is changed.
 	 * <p>
@@ -276,10 +275,12 @@ final class SearchBoxList extends JPanel {
 		if (this.searchBoxFocused) {
 			this.searchBoxEmpty = this.searchBox.getText().equals("");
 		}
-		final String searchText = this.searchBoxEmpty ? "" : this.searchBox.getText();
-		final FilterComparator comparator = new FilterComparator(searchText, this.defaultOrdering, this.caseSensitive);
+		final String searchText = this.searchBoxEmpty ? ""
+				: this.searchBox.getText();
+		final FilterComparator comparator = new FilterComparator(searchText,
+				this.defaultOrdering, this.caseSensitive);
 		final Predicate<String> searchFilter = this.getSearchFilter(searchText);
-
+		
 		// initialize list with items that match the filter then sort
 		this.listModel.clear();
 		this.itemsToFilter.forEach(string -> {
@@ -287,11 +288,20 @@ final class SearchBoxList extends JPanel {
 				this.listModel.add(string);
 			}
 		});
-
+		
 		// applies the custom filters
 		this.listModel.removeIf(this.customSearchFilter.negate());
-
+		
 		// sorts the remaining items
 		this.listModel.sort(comparator);
 	}
+	
+	/**
+	 * Manually updates the search box's item list.
+	 * 
+	 * @since 2020-08-27
+	 */
+	public void updateList() {
+		this.searchBoxTextChanged();
+	}
 }
diff --git a/src/org/unitConverter/converterGUI/UnitConverterGUI.java b/src/org/unitConverter/converterGUI/UnitConverterGUI.java
index 5fe4ee5..75ab16d 100644
--- a/src/org/unitConverter/converterGUI/UnitConverterGUI.java
+++ b/src/org/unitConverter/converterGUI/UnitConverterGUI.java
@@ -56,6 +56,7 @@ import javax.swing.JTextField;
 import javax.swing.WindowConstants;
 import javax.swing.border.TitledBorder;
 
+import org.unitConverter.math.ConditionalExistenceCollections;
 import org.unitConverter.math.ObjectProduct;
 import org.unitConverter.unit.BaseDimension;
 import org.unitConverter.unit.BritishImperial;
@@ -129,6 +130,13 @@ final class UnitConverterGUI {
 		
 		private final Comparator<String> prefixNameComparator;
 		
+		// conditions for existence of From and To entries
+		// used for one-way conversion
+		private final MutablePredicate<String> fromExistenceCondition = new MutablePredicate<>(
+				s -> true);
+		private final MutablePredicate<String> toExistenceCondition = new MutablePredicate<>(
+				s -> true);
+		
 		/*
 		 * Rounding-related settings. I am using my own system, and not
 		 * MathContext, because MathContext does not support decimal place based
@@ -338,6 +346,16 @@ final class UnitConverterGUI {
 		}
 		
 		/**
+		 * @return a list of all the entries in the dimension-based converter's
+		 *         From box
+		 * @since 2020-08-27
+		 */
+		public final Set<String> fromEntries() {
+			return ConditionalExistenceCollections.conditionalExistenceSet(
+					this.unitNameSet(), this.fromExistenceCondition);
+		}
+		
+		/**
 		 * @return a comparator to compare prefix names
 		 * @since 2019-04-14
 		 * @since v0.2.0
@@ -437,6 +455,25 @@ final class UnitConverterGUI {
 		}
 		
 		/**
+		 * Enables or disables one-way conversion.
+		 * 
+		 * @param oneWay whether one-way conversion should be on (true) or off
+		 *               (false)
+		 * @since 2020-08-27
+		 */
+		public final void setOneWay(boolean oneWay) {
+			if (oneWay) {
+				this.fromExistenceCondition.setPredicate(
+						unitName -> !this.database.getUnit(unitName).isMetric());
+				this.toExistenceCondition.setPredicate(
+						unitName -> this.database.getUnit(unitName).isMetric());
+			} else {
+				this.fromExistenceCondition.setPredicate(unitName -> true);
+				this.toExistenceCondition.setPredicate(unitName -> true);
+			}
+		}
+		
+		/**
 		 * @param precision new value of precision
 		 * @since 2019-01-15
 		 * @since v0.1.0
@@ -463,6 +500,16 @@ final class UnitConverterGUI {
 		}
 		
 		/**
+		 * @return a list of all the entries in the dimension-based converter's To
+		 *         box
+		 * @since 2020-08-27
+		 */
+		public final Set<String> toEntries() {
+			return ConditionalExistenceCollections.conditionalExistenceSet(
+					this.unitNameSet(), this.toExistenceCondition);
+		}
+		
+		/**
 		 * Returns true if and only if the unit represented by {@code unitName}
 		 * has the dimension represented by {@code dimensionName}.
 		 * 
@@ -505,7 +552,7 @@ final class UnitConverterGUI {
 		 * @since 2019-04-14
 		 * @since v0.2.0
 		 */
-		public final Set<String> unitNameSet() {
+		private final Set<String> unitNameSet() {
 			return this.database.unitMapPrefixless().keySet();
 		}
 	}
@@ -579,8 +626,8 @@ final class UnitConverterGUI {
 					this.presenter.getPrefixNameComparator(), true);
 			this.unitTextBox = new JTextArea();
 			this.prefixTextBox = new JTextArea();
-			this.fromSearch = new SearchBoxList(this.presenter.unitNameSet());
-			this.toSearch = new SearchBoxList(this.presenter.unitNameSet());
+			this.fromSearch = new SearchBoxList(this.presenter.fromEntries());
+			this.toSearch = new SearchBoxList(this.presenter.toEntries());
 			this.valueInput = new JFormattedTextField(NUMBER_FORMATTER);
 			this.dimensionBasedOutput = new JTextArea(2, 32);
 			this.fromEntry = new JTextField();
@@ -630,15 +677,6 @@ final class UnitConverterGUI {
 		}
 		
 		/**
-		 * @return text inputted into dimension-based converter
-		 * @since 2019-04-13
-		 * @since v0.2.0
-		 */
-		public String getDimensionConverterText() {
-			return this.valueInput.getText();
-		}
-		
-		/**
 		 * @return selection in "From" selector in dimension-based converter
 		 * @since 2019-04-13
 		 * @since v0.2.0
@@ -717,6 +755,9 @@ final class UnitConverterGUI {
 			{ // pane with all of the tabs
 				masterPanel.add(this.masterPane, BorderLayout.CENTER);
 				
+				// update stuff
+				this.masterPane.addChangeListener(e -> this.update());
+				
 				{ // a panel for unit conversion using a selector
 					final JPanel convertUnitPanel = new JPanel();
 					this.masterPane.addTab("Convert Units", convertUnitPanel);
@@ -1080,17 +1121,25 @@ final class UnitConverterGUI {
 								.setBorder(new TitledBorder("Miscellaneous Settings"));
 						miscPanel.setLayout(new GridBagLayout());
 						
+						final JCheckBox oneWay = new JCheckBox(
+								"Convert One Way Only");
+						oneWay.setSelected(false);
+						oneWay.addItemListener(
+								e -> this.presenter.setOneWay(e.getStateChange() == 1));
+						miscPanel.add(oneWay, new GridBagBuilder(0, 0)
+								.setAnchor(GridBagConstraints.LINE_START).build());
+						
 						final JCheckBox showAllVariations = new JCheckBox(
 								"Show Symbols in \"Convert Units\"");
 						showAllVariations.setSelected(true);
 						showAllVariations.setEnabled(false);
-						miscPanel.add(showAllVariations, new GridBagBuilder(0, 0)
+						miscPanel.add(showAllVariations, new GridBagBuilder(0, 1)
 								.setAnchor(GridBagConstraints.LINE_START).build());
 						
 						final JButton unitFileButton = new JButton(
 								"Manage Unit Data Files");
 						unitFileButton.setEnabled(false);
-						miscPanel.add(unitFileButton, new GridBagBuilder(0, 1)
+						miscPanel.add(unitFileButton, new GridBagBuilder(0, 2)
 								.setAnchor(GridBagConstraints.LINE_START).build());
 					}
 				}
@@ -1153,6 +1202,18 @@ final class UnitConverterGUI {
 			JOptionPane.showMessageDialog(this.frame, message, title,
 					JOptionPane.ERROR_MESSAGE);
 		}
+		
+		public void update() {
+			switch (this.getActivePane()) {
+			case UNIT_CONVERTER:
+				this.fromSearch.updateList();
+				this.toSearch.updateList();
+				break;
+			default:
+				// do nothing, for now
+				break;
+			}
+		}
 	}
 	
 	public static void main(final String[] args) {
diff --git a/src/org/unitConverter/unit/SI.java b/src/org/unitConverter/unit/SI.java
index a4fbd5f..f36cf28 100644
--- a/src/org/unitConverter/unit/SI.java
+++ b/src/org/unitConverter/unit/SI.java
@@ -17,6 +17,7 @@
 package org.unitConverter.unit;

 

 import java.util.Arrays;

+import java.util.Collections;

 import java.util.HashSet;

 import java.util.Set;

 

@@ -91,6 +92,9 @@ public final class SI {
 		public static final BaseUnit DOLLAR = BaseUnit

 				.valueOf(BaseDimensions.CURRENCY, "dollar", "$");

 		

+		public static final Set<BaseUnit> BASE_UNITS = setOf(METRE, KILOGRAM,

+				SECOND, AMPERE, KELVIN, MOLE, CANDELA, BIT);

+		

 		// You may NOT get SI.BaseUnits instances!

 		private BaseUnits() {

 			throw new AssertionError();

@@ -210,6 +214,7 @@ public final class SI {
 	/// The units of the SI

 	public static final LinearUnit ONE = LinearUnit

 			.valueOf(ObjectProduct.empty(), 1);

+	

 	public static final LinearUnit METRE = BaseUnits.METRE.asLinearUnit()

 			.withName(NameSymbol.of("metre", "m", "meter"));

 	public static final LinearUnit KILOGRAM = BaseUnits.KILOGRAM.asLinearUnit()

@@ -228,10 +233,10 @@ public final class SI {
 			.withName(NameSymbol.of("bit", "b"));

 	public static final LinearUnit DOLLAR = BaseUnits.DOLLAR.asLinearUnit()

 			.withName(NameSymbol.of("dollar", "$"));

-	

 	// Non-base units

 	public static final LinearUnit RADIAN = METRE.dividedBy(METRE)

 			.withName(NameSymbol.of("radian", "rad"));

+	

 	public static final LinearUnit STERADIAN = RADIAN.times(RADIAN)

 			.withName(NameSymbol.of("steradian", "sr"));

 	public static final LinearUnit HERTZ = ONE.dividedBy(SECOND)

@@ -277,10 +282,10 @@ public final class SI {
 	// for dose equivalent

 	public static final LinearUnit KATAL = MOLE.dividedBy(SECOND)

 			.withName(NameSymbol.of("katal", "kat"));

-	

 	// common derived units included for convenience

 	public static final LinearUnit GRAM = KILOGRAM.dividedBy(1000)

 			.withName(NameSymbol.of("gram", "g"));

+	

 	public static final LinearUnit SQUARE_METRE = METRE.toExponent(2)

 			.withName(NameSymbol.of("square metre", "m^2", "square meter",

 					"metre squared", "meter squared"));

@@ -290,12 +295,12 @@ public final class SI {
 	public static final LinearUnit METRE_PER_SECOND = METRE.dividedBy(SECOND)

 			.withName(

 					NameSymbol.of("metre per second", "m/s", "meter per second"));

-	

 	// Non-SI units included for convenience

 	public static final Unit CELSIUS = Unit

 			.fromConversionFunctions(KELVIN.getBase(), tempK -> tempK - 273.15,

 					tempC -> tempC + 273.15)

 			.withName(NameSymbol.of("degree Celsius", "\u00B0C"));

+	

 	public static final LinearUnit MINUTE = SECOND.times(60)

 			.withName(NameSymbol.of("minute", "min"));

 	public static final LinearUnit HOUR = MINUTE.times(60)

@@ -324,7 +329,7 @@ public final class SI {
 			.withName(NameSymbol.of("tonne", "t", "metric ton"));

 	public static final LinearUnit DALTON = KILOGRAM.times(1.660539040e-27)

 			.withName(NameSymbol.of("dalton", "Da", "atomic unit", "u")); // approximate

-																								// value

+	// value

 	public static final LinearUnit ELECTRONVOLT = JOULE.times(1.602176634e-19)

 			.withName(NameSymbol.of("electron volt", "eV"));

 	public static final LinearUnit BYTE = BIT.times(8)

@@ -339,11 +344,11 @@ public final class SI {
 			.fromConversionFunctions(ONE.getBase(), pr -> 10 * Math.log10(pr),

 					dB -> Math.pow(10, dB / 10))

 			.withName(NameSymbol.of("decibel", "dB"));

-	

 	/// The prefixes of the SI

 	// expanding decimal prefixes

 	public static final UnitPrefix KILO = UnitPrefix.valueOf(1e3)

 			.withName(NameSymbol.of("kilo", "k", "K"));

+	

 	public static final UnitPrefix MEGA = UnitPrefix.valueOf(1e6)

 			.withName(NameSymbol.of("mega", "M"));

 	public static final UnitPrefix GIGA = UnitPrefix.valueOf(1e9)

@@ -358,10 +363,10 @@ public final class SI {
 			.withName(NameSymbol.of("zetta", "Z"));

 	public static final UnitPrefix YOTTA = UnitPrefix.valueOf(1e24)

 			.withName(NameSymbol.of("yotta", "Y"));

-	

 	// contracting decimal prefixes

 	public static final UnitPrefix MILLI = UnitPrefix.valueOf(1e-3)

 			.withName(NameSymbol.of("milli", "m"));

+	

 	public static final UnitPrefix MICRO = UnitPrefix.valueOf(1e-6)

 			.withName(NameSymbol.of("micro", "\u03BC", "u")); // mu

 	public static final UnitPrefix NANO = UnitPrefix.valueOf(1e-9)

@@ -376,10 +381,10 @@ public final class SI {
 			.withName(NameSymbol.of("zepto", "z"));

 	public static final UnitPrefix YOCTO = UnitPrefix.valueOf(1e-24)

 			.withName(NameSymbol.of("yocto", "y"));

-	

 	// prefixes that don't match the pattern of thousands

 	public static final UnitPrefix DEKA = UnitPrefix.valueOf(1e1)

 			.withName(NameSymbol.of("deka", "da", "deca", "D"));

+	

 	public static final UnitPrefix HECTO = UnitPrefix.valueOf(1e2)

 			.withName(NameSymbol.of("hecto", "h", "H", "hekto"));

 	public static final UnitPrefix DECI = UnitPrefix.valueOf(1e-1)

@@ -398,25 +403,29 @@ public final class SI {
 			.withName(NameSymbol.of("pebi", "Pi"));

 	public static final UnitPrefix EXBI = PEBI.times(1024)

 			.withName(NameSymbol.of("exbi", "Ei"));

-	

 	// sets of prefixes

-	public static final Set<UnitPrefix> ALL_PREFIXES = new HashSet<>(

-			Arrays.asList(DEKA, HECTO, KILO, MEGA, GIGA, TERA, PETA, EXA, ZETTA,

-					YOTTA, DECI, CENTI, MILLI, MICRO, NANO, PICO, FEMTO, ATTO, ZEPTO,

-					YOCTO, KIBI, MEBI, GIBI, TEBI, PEBI, EXBI));

-	public static final Set<UnitPrefix> DECIMAL_PREFIXES = new HashSet<>(

-			Arrays.asList(DEKA, HECTO, KILO, MEGA, GIGA, TERA, PETA, EXA, ZETTA,

-					YOTTA, DECI, CENTI, MILLI, MICRO, NANO, PICO, FEMTO, ATTO, ZEPTO,

-					YOCTO));

-	public static final Set<UnitPrefix> THOUSAND_PREFIXES = new HashSet<>(

-			Arrays.asList(KILO, MEGA, GIGA, TERA, PETA, EXA, ZETTA, YOTTA, MILLI,

-					MICRO, NANO, PICO, FEMTO, ATTO, ZEPTO, YOCTO));

-	public static final Set<UnitPrefix> MAGNIFYING_PREFIXES = new HashSet<>(

-			Arrays.asList(DEKA, HECTO, KILO, MEGA, GIGA, TERA, PETA, EXA, ZETTA,

-					YOTTA, KIBI, MEBI, GIBI, TEBI, PEBI, EXBI));

-	public static final Set<UnitPrefix> REDUCING_PREFIXES = new HashSet<>(

-			Arrays.asList(DECI, CENTI, MILLI, MICRO, NANO, PICO, FEMTO, ATTO,

-					ZEPTO, YOCTO));

+	public static final Set<UnitPrefix> ALL_PREFIXES = setOf(DEKA, HECTO, KILO,

+			MEGA, GIGA, TERA, PETA, EXA, ZETTA, YOTTA, DECI, CENTI, MILLI, MICRO,

+			NANO, PICO, FEMTO, ATTO, ZEPTO, YOCTO, KIBI, MEBI, GIBI, TEBI, PEBI,

+			EXBI);

+	

+	public static final Set<UnitPrefix> DECIMAL_PREFIXES = setOf(DEKA, HECTO,

+			KILO, MEGA, GIGA, TERA, PETA, EXA, ZETTA, YOTTA, DECI, CENTI, MILLI,

+			MICRO, NANO, PICO, FEMTO, ATTO, ZEPTO, YOCTO);

+	public static final Set<UnitPrefix> THOUSAND_PREFIXES = setOf(KILO, MEGA,

+			GIGA, TERA, PETA, EXA, ZETTA, YOTTA, MILLI, MICRO, NANO, PICO, FEMTO,

+			ATTO, ZEPTO, YOCTO);

+	public static final Set<UnitPrefix> MAGNIFYING_PREFIXES = setOf(DEKA, HECTO,

+			KILO, MEGA, GIGA, TERA, PETA, EXA, ZETTA, YOTTA, KIBI, MEBI, GIBI,

+			TEBI, PEBI, EXBI);

+	public static final Set<UnitPrefix> REDUCING_PREFIXES = setOf(DECI, CENTI,

+			MILLI, MICRO, NANO, PICO, FEMTO, ATTO, ZEPTO, YOCTO);

+	

+	// this method just calls Arrays.asList, which is itself safe.

+	@SafeVarargs

+	private static final <T> Set<T> setOf(T... args) {

+		return Collections.unmodifiableSet(new HashSet<>(Arrays.asList(args)));

+	}

 	

 	// You may NOT get SI instances!

 	private SI() {

diff --git a/src/org/unitConverter/unit/Unit.java b/src/org/unitConverter/unit/Unit.java
index 35b32fc..eb9b000 100644
--- a/src/org/unitConverter/unit/Unit.java
+++ b/src/org/unitConverter/unit/Unit.java
@@ -25,6 +25,7 @@ import java.util.Optional;
 import java.util.Set;
 import java.util.function.DoubleUnaryOperator;
 
+import org.unitConverter.math.DecimalComparison;
 import org.unitConverter.math.ObjectProduct;
 
 /**
@@ -35,209 +36,211 @@ import org.unitConverter.math.ObjectProduct;
  */
 public abstract class Unit {
 	/**
-	 * Returns a unit from its base and the functions it uses to convert to and from its base.
+	 * Returns a unit from its base and the functions it uses to convert to and
+	 * from its base.
 	 * 
 	 * <p>
-	 * For example, to get a unit representing the degree Celsius, the following code can be used:
+	 * For example, to get a unit representing the degree Celsius, the following
+	 * code can be used:
 	 * 
 	 * {@code Unit.fromConversionFunctions(SI.KELVIN, tempK -> tempK - 273.15, tempC -> tempC + 273.15);}
 	 * </p>
 	 * 
-	 * @param base
-	 *            unit's base
-	 * @param converterFrom
-	 *            function that accepts a value expressed in the unit's base and returns that value expressed in this
-	 *            unit.
-	 * @param converterTo
-	 *            function that accepts a value expressed in the unit and returns that value expressed in the unit's
-	 *            base.
+	 * @param base          unit's base
+	 * @param converterFrom function that accepts a value expressed in the unit's
+	 *                      base and returns that value expressed in this unit.
+	 * @param converterTo   function that accepts a value expressed in the unit
+	 *                      and returns that value expressed in the unit's base.
 	 * @return a unit that uses the provided functions to convert.
 	 * @since 2019-05-22
-	 * @throws NullPointerException
-	 *             if any argument is null
+	 * @throws NullPointerException if any argument is null
 	 */
-	public static final Unit fromConversionFunctions(final ObjectProduct<BaseUnit> base,
-			final DoubleUnaryOperator converterFrom, final DoubleUnaryOperator converterTo) {
+	public static final Unit fromConversionFunctions(
+			final ObjectProduct<BaseUnit> base,
+			final DoubleUnaryOperator converterFrom,
+			final DoubleUnaryOperator converterTo) {
 		return new FunctionalUnit(base, converterFrom, converterTo);
 	}
-
+	
 	/**
-	 * Returns a unit from its base and the functions it uses to convert to and from its base.
+	 * Returns a unit from its base and the functions it uses to convert to and
+	 * from its base.
 	 * 
 	 * <p>
-	 * For example, to get a unit representing the degree Celsius, the following code can be used:
+	 * For example, to get a unit representing the degree Celsius, the following
+	 * code can be used:
 	 * 
 	 * {@code Unit.fromConversionFunctions(SI.KELVIN, tempK -> tempK - 273.15, tempC -> tempC + 273.15);}
 	 * </p>
 	 * 
-	 * @param base
-	 *            unit's base
-	 * @param converterFrom
-	 *            function that accepts a value expressed in the unit's base and returns that value expressed in this
-	 *            unit.
-	 * @param converterTo
-	 *            function that accepts a value expressed in the unit and returns that value expressed in the unit's
-	 *            base.
-	 * @param ns
-	 *            names and symbol of unit
+	 * @param base          unit's base
+	 * @param converterFrom function that accepts a value expressed in the unit's
+	 *                      base and returns that value expressed in this unit.
+	 * @param converterTo   function that accepts a value expressed in the unit
+	 *                      and returns that value expressed in the unit's base.
+	 * @param ns            names and symbol of unit
 	 * @return a unit that uses the provided functions to convert.
 	 * @since 2019-05-22
-	 * @throws NullPointerException
-	 *             if any argument is null
+	 * @throws NullPointerException if any argument is null
 	 */
-	public static final Unit fromConversionFunctions(final ObjectProduct<BaseUnit> base,
-			final DoubleUnaryOperator converterFrom, final DoubleUnaryOperator converterTo, final NameSymbol ns) {
+	public static final Unit fromConversionFunctions(
+			final ObjectProduct<BaseUnit> base,
+			final DoubleUnaryOperator converterFrom,
+			final DoubleUnaryOperator converterTo, final NameSymbol ns) {
 		return new FunctionalUnit(base, converterFrom, converterTo, ns);
 	}
-
+	
 	/**
 	 * The combination of units that this unit is based on.
 	 * 
 	 * @since 2019-10-16
 	 */
 	private final ObjectProduct<BaseUnit> unitBase;
-
+	
 	/**
 	 * The primary name used by this unit.
 	 */
 	private final Optional<String> primaryName;
-
+	
 	/**
 	 * A short symbol used to represent this unit.
 	 */
 	private final Optional<String> symbol;
-
+	
 	/**
 	 * A set of any additional names and/or spellings that the unit uses.
 	 */
 	private final Set<String> otherNames;
-
+	
 	/**
 	 * Cache storing the result of getDimension()
 	 *
 	 * @since 2019-10-16
 	 */
 	private transient ObjectProduct<BaseDimension> dimension = null;
-
+	
 	/**
 	 * Creates the {@code AbstractUnit}.
 	 * 
-	 * @param unitBase
-	 *            base of unit
-	 * @param ns
-	 *            names and symbol of unit
+	 * @param unitBase base of unit
+	 * @param ns       names and symbol of unit
 	 * @since 2019-10-16
-	 * @throws NullPointerException
-	 *             if unitBase or ns is null
+	 * @throws NullPointerException if unitBase or ns is null
 	 */
 	protected Unit(final ObjectProduct<BaseUnit> unitBase, final NameSymbol ns) {
-		this.unitBase = Objects.requireNonNull(unitBase, "unitBase must not be null.");
-		this.primaryName = Objects.requireNonNull(ns, "ns must not be null.").getPrimaryName();
+		this.unitBase = Objects.requireNonNull(unitBase,
+				"unitBase must not be null.");
+		this.primaryName = Objects.requireNonNull(ns, "ns must not be null.")
+				.getPrimaryName();
 		this.symbol = ns.getSymbol();
 		this.otherNames = ns.getOtherNames();
 	}
-
+	
 	/**
 	 * A constructor that constructs {@code BaseUnit} instances.
 	 * 
 	 * @since 2019-10-16
 	 */
-	Unit(final String primaryName, final String symbol, final Set<String> otherNames) {
+	Unit(final String primaryName, final String symbol,
+			final Set<String> otherNames) {
 		if (this instanceof BaseUnit) {
 			this.unitBase = ObjectProduct.oneOf((BaseUnit) this);
 		} else
 			throw new AssertionError();
 		this.primaryName = Optional.of(primaryName);
 		this.symbol = Optional.of(symbol);
-		this.otherNames = Collections.unmodifiableSet(
-				new HashSet<>(Objects.requireNonNull(otherNames, "additionalNames must not be null.")));
+		this.otherNames = Collections.unmodifiableSet(new HashSet<>(Objects
+				.requireNonNull(otherNames, "additionalNames must not be null.")));
 	}
-
+	
 	/**
-	 * Checks if a value expressed in this unit can be converted to a value expressed in {@code other}
+	 * Checks if a value expressed in this unit can be converted to a value
+	 * expressed in {@code other}
 	 * 
-	 * @param other
-	 *            unit to test with
+	 * @param other unit to test with
 	 * @return true if the units are compatible
 	 * @since 2019-01-13
 	 * @since v0.1.0
-	 * @throws NullPointerException
-	 *             if other is null
+	 * @throws NullPointerException if other is null
 	 */
 	public final boolean canConvertTo(final Unit other) {
 		Objects.requireNonNull(other, "other must not be null.");
 		return Objects.equals(this.getBase(), other.getBase());
 	}
-
+	
 	/**
-	 * Converts from a value expressed in this unit's base unit to a value expressed in this unit.
+	 * Converts from a value expressed in this unit's base unit to a value
+	 * expressed in this unit.
 	 * <p>
-	 * This must be the inverse of {@code convertToBase}, so {@code convertFromBase(convertToBase(value))} must be equal
-	 * to {@code value} for any value, ignoring precision loss by roundoff error.
+	 * This must be the inverse of {@code convertToBase}, so
+	 * {@code convertFromBase(convertToBase(value))} must be equal to
+	 * {@code value} for any value, ignoring precision loss by roundoff error.
 	 * </p>
 	 * <p>
-	 * If this unit <i>is</i> a base unit, this method should return {@code value}.
+	 * If this unit <i>is</i> a base unit, this method should return
+	 * {@code value}.
 	 * </p>
 	 * 
-	 * @implSpec This method is used by {@link #convertTo}, and its behaviour affects the behaviour of
-	 *           {@code convertTo}.
+	 * @implSpec This method is used by {@link #convertTo}, and its behaviour
+	 *           affects the behaviour of {@code convertTo}.
 	 * 
-	 * @param value
-	 *            value expressed in <b>base</b> unit
+	 * @param value value expressed in <b>base</b> unit
 	 * @return value expressed in <b>this</b> unit
 	 * @since 2018-12-22
 	 * @since v0.1.0
 	 */
 	protected abstract double convertFromBase(double value);
-
+	
 	/**
-	 * Converts a value expressed in this unit to a value expressed in {@code other}.
+	 * Converts a value expressed in this unit to a value expressed in
+	 * {@code other}.
 	 * 
 	 * @implSpec If unit conversion is possible, this implementation returns
-	 *           {@code other.convertFromBase(this.convertToBase(value))}. Therefore, overriding either of those methods
-	 *           will change the output of this method.
+	 *           {@code other.convertFromBase(this.convertToBase(value))}.
+	 *           Therefore, overriding either of those methods will change the
+	 *           output of this method.
 	 * 
-	 * @param other
-	 *            unit to convert to
-	 * @param value
-	 *            value to convert
+	 * @param other unit to convert to
+	 * @param value value to convert
 	 * @return converted value
 	 * @since 2019-05-22
-	 * @throws IllegalArgumentException
-	 *             if {@code other} is incompatible for conversion with this unit (as tested by
-	 *             {@link Unit#canConvertTo}).
-	 * @throws NullPointerException
-	 *             if other is null
+	 * @throws IllegalArgumentException if {@code other} is incompatible for
+	 *                                  conversion with this unit (as tested by
+	 *                                  {@link Unit#canConvertTo}).
+	 * @throws NullPointerException     if other is null
 	 */
 	public final double convertTo(final Unit other, final double value) {
 		Objects.requireNonNull(other, "other must not be null.");
 		if (this.canConvertTo(other))
 			return other.convertFromBase(this.convertToBase(value));
 		else
-			throw new IllegalArgumentException(String.format("Cannot convert from %s to %s.", this, other));
+			throw new IllegalArgumentException(
+					String.format("Cannot convert from %s to %s.", this, other));
 	}
-
+	
 	/**
-	 * Converts from a value expressed in this unit to a value expressed in this unit's base unit.
+	 * Converts from a value expressed in this unit to a value expressed in this
+	 * unit's base unit.
 	 * <p>
-	 * This must be the inverse of {@code convertFromBase}, so {@code convertToBase(convertFromBase(value))} must be
-	 * equal to {@code value} for any value, ignoring precision loss by roundoff error.
+	 * This must be the inverse of {@code convertFromBase}, so
+	 * {@code convertToBase(convertFromBase(value))} must be equal to
+	 * {@code value} for any value, ignoring precision loss by roundoff error.
 	 * </p>
 	 * <p>
-	 * If this unit <i>is</i> a base unit, this method should return {@code value}.
+	 * If this unit <i>is</i> a base unit, this method should return
+	 * {@code value}.
 	 * </p>
 	 * 
-	 * @implSpec This method is used by {@link #convertTo}, and its behaviour affects the behaviour of
-	 *           {@code convertTo}.
+	 * @implSpec This method is used by {@link #convertTo}, and its behaviour
+	 *           affects the behaviour of {@code convertTo}.
 	 * 
-	 * @param value
-	 *            value expressed in <b>this</b> unit
+	 * @param value value expressed in <b>this</b> unit
 	 * @return value expressed in <b>base</b> unit
 	 * @since 2018-12-22
 	 * @since v0.1.0
 	 */
 	protected abstract double convertToBase(double value);
-
+	
 	/**
 	 * @return combination of units that this unit is based on
 	 * @since 2018-12-22
@@ -246,7 +249,7 @@ public abstract class Unit {
 	public final ObjectProduct<BaseUnit> getBase() {
 		return this.unitBase;
 	}
-
+	
 	/**
 	 * @return dimension measured by this unit
 	 * @since 2018-12-22
@@ -256,16 +259,16 @@ public abstract class Unit {
 		if (this.dimension == null) {
 			final Map<BaseUnit, Integer> mapping = this.unitBase.exponentMap();
 			final Map<BaseDimension, Integer> dimensionMap = new HashMap<>();
-
+			
 			for (final BaseUnit key : mapping.keySet()) {
 				dimensionMap.put(key.getBaseDimension(), mapping.get(key));
 			}
-
+			
 			this.dimension = ObjectProduct.fromExponentMapping(dimensionMap);
 		}
 		return this.dimension;
 	}
-
+	
 	/**
 	 * @return additionalNames
 	 * @since 2019-10-21
@@ -273,7 +276,7 @@ public abstract class Unit {
 	public final Set<String> getOtherNames() {
 		return this.otherNames;
 	}
-
+	
 	/**
 	 * @return primaryName
 	 * @since 2019-10-21
@@ -281,7 +284,7 @@ public abstract class Unit {
 	public final Optional<String> getPrimaryName() {
 		return this.primaryName;
 	}
-
+	
 	/**
 	 * @return symbol
 	 * @since 2019-10-21
@@ -289,25 +292,64 @@ public abstract class Unit {
 	public final Optional<String> getSymbol() {
 		return this.symbol;
 	}
-
+	
+	/**
+	 * Returns true iff this unit is metric.
+	 * <p>
+	 * "Metric" is defined by three conditions:
+	 * <ul>
+	 * <li>Must be an instance of {@link LinearUnit}.</li>
+	 * <li>Must be based on the SI base units (as determined by getBase())</li>
+	 * <li>The conversion factor must be a power of 10.</li>
+	 * </ul>
+	 * <p>
+	 * Note that this definition excludes some units that many would consider
+	 * "metric", such as the degree Celsius (fails the first condition),
+	 * calories, minutes and hours (fail the third condition).
+	 * <p>
+	 * All SI units (as designated by the BIPM) except the degree Celsius are
+	 * considered "metric" by this definition.
+	 * 
+	 * @since 2020-08-27
+	 */
+	public final boolean isMetric() {
+		// first condition - check that it is a linear unit
+		if (!(this instanceof LinearUnit))
+			return false;
+		final LinearUnit linear = (LinearUnit) this;
+		
+		// second condition - check that
+		for (final BaseUnit b : linear.getBase().getBaseSet()) {
+			if (!SI.BaseUnits.BASE_UNITS.contains(b))
+				return false;
+		}
+		
+		// third condition - check that conversion factor is a power of 10
+		return DecimalComparison
+				.equals(Math.log10(linear.getConversionFactor()) % 1.0, 0);
+	}
+	
 	@Override
 	public String toString() {
 		return this.getPrimaryName().orElse("Unnamed unit")
-				+ (this.getSymbol().isPresent() ? String.format(" (%s)", this.getSymbol().get()) : "")
-				+ ", derived from " + this.getBase().toString(u -> u.getSymbol().get())
-				+ (this.getOtherNames().isEmpty() ? "" : ", also called " + String.join(", ", this.getOtherNames()));
+				+ (this.getSymbol().isPresent()
+						? String.format(" (%s)", this.getSymbol().get())
+						: "")
+				+ ", derived from "
+				+ this.getBase().toString(u -> u.getSymbol().get())
+				+ (this.getOtherNames().isEmpty() ? ""
+						: ", also called " + String.join(", ", this.getOtherNames()));
 	}
-
+	
 	/**
-	 * @param ns
-	 *            name(s) and symbol to use
+	 * @param ns name(s) and symbol to use
 	 * @return a copy of this unit with provided name(s) and symbol
 	 * @since 2019-10-21
-	 * @throws NullPointerException
-	 *             if ns is null
+	 * @throws NullPointerException if ns is null
 	 */
 	public Unit withName(final NameSymbol ns) {
-		return fromConversionFunctions(this.getBase(), this::convertFromBase, this::convertToBase,
+		return fromConversionFunctions(this.getBase(), this::convertFromBase,
+				this::convertToBase,
 				Objects.requireNonNull(ns, "ns must not be null."));
 	}
 }
diff --git a/src/org/unitConverter/unit/UnitTest.java b/src/org/unitConverter/unit/UnitTest.java
index 2cf3126..ff83805 100644
--- a/src/org/unitConverter/unit/UnitTest.java
+++ b/src/org/unitConverter/unit/UnitTest.java
@@ -16,6 +16,7 @@
  */
 package org.unitConverter.unit;
 
+import static org.junit.Assert.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
@@ -105,6 +106,17 @@ class UnitTest {
 	}
 	
 	@Test
+	public void testIsMetric() {
+		final Unit metre = SI.METRE;
+		final Unit megasecond = SI.SECOND.withPrefix(SI.MEGA);
+		final Unit hour = SI.HOUR;
+		
+		assertTrue(metre.isMetric());
+		assertTrue(megasecond.isMetric());
+		assertFalse(hour.isMetric());
+	}
+	
+	@Test
 	public void testMultiplicationAndDivision() {
 		// test unit-times-unit multiplication
 		final LinearUnit generatedJoule = SI.KILOGRAM