Added unit prefixes and made SI reuse base units.

1 files changed, 24 insertions, 1 deletions

diff --git a/src/unitConverter/unit/SI.java b/src/unitConverter/unit/SI.java
index 4486bf9..cda42e7 100644
--- a/src/unitConverter/unit/SI.java
+++ b/src/unitConverter/unit/SI.java
@@ -16,6 +16,10 @@
  */
 package unitConverter.unit;
 
+import java.util.HashSet;
+import java.util.Objects;
+import java.util.Set;
+
 import unitConverter.dimension.StandardDimensions;
 import unitConverter.dimension.UnitDimension;
 
@@ -28,6 +32,13 @@ import unitConverter.dimension.UnitDimension;
 public enum SI implements UnitSystem {
 	SI;
 
+	/**
+	 * This system's base units.
+	 * 
+	 * @since 2019-01-25
+	 */
+	private static final Set<BaseUnit> baseUnits = new HashSet<>();
+
 	// base units
 	public static final BaseUnit METRE = SI.getBaseUnit(StandardDimensions.LENGTH);
 	public static final BaseUnit KILOGRAM = SI.getBaseUnit(StandardDimensions.MASS);
@@ -39,7 +50,19 @@ public enum SI implements UnitSystem {
 
 	@Override
 	public BaseUnit getBaseUnit(final UnitDimension dimension) {
-		return new BaseUnit(dimension, this);
+		// try to find an existing unit before creating a new one
+
+		Objects.requireNonNull(dimension, "dimension must not be null.");
+		for (final BaseUnit unit : baseUnits) {
+			// it will be equal since the conditions for equality are dimension and system,
+			// and system is always SI.
+			if (unit.getDimension().equals(dimension))
+				return unit;
+		}
+		// could not find an existing base unit
+		final BaseUnit unit = new BaseUnit(dimension, this);
+		baseUnits.add(unit);
+		return unit;
 	}
 
 	@Override