1 files changed, 33 insertions, 2 deletions
diff --git a/src/org/unitConverter/converterGUI/UnitConverterGUI.java b/src/org/unitConverter/converterGUI/UnitConverterGUI.java
index 75ab16d..38a9de1 100644
--- a/src/org/unitConverter/converterGUI/UnitConverterGUI.java
+++ b/src/org/unitConverter/converterGUI/UnitConverterGUI.java
@@ -21,7 +21,10 @@ import java.awt.GridBagConstraints;
 import java.awt.GridBagLayout;
 import java.awt.GridLayout;
 import java.awt.event.KeyEvent;
+import java.io.BufferedReader;
 import java.io.File;
+import java.io.FileReader;
+import java.io.IOException;
 import java.math.BigDecimal;
 import java.math.MathContext;
 import java.math.RoundingMode;
@@ -128,6 +131,9 @@ final class UnitConverterGUI {
 		/** The names of all of the dimensions */
 		private final List<String> dimensionNames;
 		
+		/** Unit names that are ignored by the metric-only/imperial-only filter */
+		private final Set<String> metricExceptions;
+		
 		private final Comparator<String> prefixNameComparator;
 		
 		// conditions for existence of From and To entries
@@ -164,6 +170,29 @@ final class UnitConverterGUI {
 			this.database.loadUnitsFile(new File("unitsfile.txt"));
 			this.database.loadDimensionFile(new File("dimensionfile.txt"));
 			
+			// load metric exceptions
+			final File exceptions = new File("metric_exceptions.txt");
+			this.metricExceptions = new HashSet<>();
+			try (FileReader fileReader = new FileReader(exceptions);
+					BufferedReader reader = new BufferedReader(fileReader)) {
+				while (reader.ready()) {
+					String line = reader.readLine();
+					
+					// # can be used for comments
+					if (line.contains("#")) {
+						line = line.substring(line.indexOf("#"));
+					}
+					
+					// don't read black lines
+					if (!line.isBlank()) {
+						this.metricExceptions.add(line.strip());
+					}
+				}
+			} catch (final IOException e) {
+				throw new AssertionError("Loading of metric_exceptions.txt failed.",
+						e);
+			}
+			
 			// a comparator that can be used to compare prefix names
 			// any name that does not exist is less than a name that does.
 			// otherwise, they are compared by value
@@ -464,9 +493,11 @@ final class UnitConverterGUI {
 		public final void setOneWay(boolean oneWay) {
 			if (oneWay) {
 				this.fromExistenceCondition.setPredicate(
-						unitName -> !this.database.getUnit(unitName).isMetric());
+						unitName -> this.metricExceptions.contains(unitName)
+								|| !this.database.getUnit(unitName).isMetric());
 				this.toExistenceCondition.setPredicate(
-						unitName -> this.database.getUnit(unitName).isMetric());
+						unitName -> this.metricExceptions.contains(unitName)
+								|| this.database.getUnit(unitName).isMetric());
 			} else {
 				this.fromExistenceCondition.setPredicate(unitName -> true);
 				this.toExistenceCondition.setPredicate(unitName -> true);