1 files changed, 56 insertions, 1 deletions

diff --git a/src/org/unitConverter/unit/LinearUnit.java b/src/org/unitConverter/unit/LinearUnit.java
index ab46f1e..64eff1f 100644
--- a/src/org/unitConverter/unit/LinearUnit.java
+++ b/src/org/unitConverter/unit/LinearUnit.java
@@ -27,7 +27,7 @@ import org.unitConverter.dimension.UnitDimension;
  * @since 2018-12-22
  * @since v0.1.0
  */
-public final class LinearUnit extends AbstractUnit {
+public final class LinearUnit extends AbstractUnit implements OperatableUnit {
 	/**
 	 * The value of one of this unit in this unit's base unit
 	 * 
@@ -134,6 +134,40 @@ public final class LinearUnit extends AbstractUnit {
 		return result;
 	}
 
+	@Override
+	public LinearUnit negated() {
+		return new LinearUnit(this.getBase(), -this.getConversionFactor());
+	}
+
+	@Override
+	public OperatableUnit plus(final OperatableUnit addend) {
+		Objects.requireNonNull(addend, "addend must not be null.");
+
+		// reject addends that cannot be added to this unit
+		if (!this.getSystem().equals(addend.getSystem()))
+			throw new IllegalArgumentException(
+					String.format("Incompatible units for addition or subtraction \"%s\" and \"%s\".", this, addend));
+		if (!this.getDimension().equals(addend.getDimension()))
+			throw new IllegalArgumentException(
+					String.format("Incompatible units for addition or subtraction \"%s\" and \"%s\".", this, addend));
+
+		// add the units
+		if (addend instanceof BaseUnit)
+			// since addend's dimension is equal to this unit's dimension, and there is only one base unit per
+			// system-dimension, addend must be this unit's base.
+			return new LinearUnit(this.getBase(), this.getConversionFactor() + 1);
+		else if (addend instanceof LinearUnit)
+			return new LinearUnit(this.getBase(),
+					this.getConversionFactor() + ((LinearUnit) addend).getConversionFactor());
+		else
+			return addend.times(this);
+	}
+
+	@Override
+	public LinearUnit reciprocal() {
+		return this.toExponent(-1);
+	}
+
 	/**
 	 * Multiplies this unit by a scalar.
 	 * 
@@ -164,6 +198,26 @@ public final class LinearUnit extends AbstractUnit {
 		return new LinearUnit(base, this.getConversionFactor() * other.getConversionFactor());
 	}
 
+	@Override
+	public OperatableUnit times(final OperatableUnit multiplier) {
+		Objects.requireNonNull(multiplier, "multiplier must not be null.");
+
+		// reject multipliers that cannot be muliplied by this unit
+		if (!this.getSystem().equals(multiplier.getSystem()))
+			throw new IllegalArgumentException(String
+					.format("Incompatible units for multiplication or division \"%s\" and \"%s\".", this, multiplier));
+
+		// multiply the units
+		if (multiplier instanceof BaseUnit) {
+			final BaseUnit newBase = this.getBase().times((BaseUnit) multiplier);
+			return new LinearUnit(newBase, this.getConversionFactor());
+		} else if (multiplier instanceof LinearUnit) {
+			final BaseUnit base = this.getBase().times(multiplier.getBase());
+			return new LinearUnit(base, this.getConversionFactor() * ((LinearUnit) multiplier).getConversionFactor());
+		} else
+			return multiplier.times(this);
+	}
+
 	/**
 	 * Returns this unit but to an exponent.
 	 * 
@@ -173,6 +227,7 @@ public final class LinearUnit extends AbstractUnit {
 	 * @since 2019-01-15
 	 * @since v0.1.0
 	 */
+	@Override
 	public LinearUnit toExponent(final int exponent) {
 		return new LinearUnit(this.getBase().toExponent(exponent), Math.pow(this.conversionFactor, exponent));
 	}