4 files changed, 280 insertions, 1 deletions
diff --git a/src/org/unitConverter/newUnits/AbstractUnit.java b/src/org/unitConverter/newUnits/AbstractUnit.java
index 909ea8b..bc4608e 100644
--- a/src/org/unitConverter/newUnits/AbstractUnit.java
+++ b/src/org/unitConverter/newUnits/AbstractUnit.java
@@ -60,7 +60,7 @@ public abstract class AbstractUnit implements Unit {
 	}
 
 	@Override
-	public ObjectProduct<BaseDimension> getDimension() {
+	public final ObjectProduct<BaseDimension> getDimension() {
 		if (this.dimension == null) {
 			final Map<BaseUnit, Integer> mapping = this.unitBase.exponentMap();
 			final Map<BaseDimension, Integer> dimensionMap = new HashMap<>();
@@ -73,4 +73,9 @@ public abstract class AbstractUnit implements Unit {
 		}
 		return this.dimension;
 	}
+
+	@Override
+	public String toString() {
+		return "Unit derived from base " + this.getBase().toString();
+	}
 }
diff --git a/src/org/unitConverter/newUnits/BaseUnit.java b/src/org/unitConverter/newUnits/BaseUnit.java
index 69e8b8b..b7577ff 100644
--- a/src/org/unitConverter/newUnits/BaseUnit.java
+++ b/src/org/unitConverter/newUnits/BaseUnit.java
@@ -51,6 +51,17 @@ public final class BaseUnit implements Unit {
 		this.symbol = Objects.requireNonNull(symbol, "symbol must not be null.");
 	}
 
+	/**
+	 * Returns a {@code LinearUnit} with this unit as a base and a conversion factor of 1. This operation must be done
+	 * in order to allow units to be created with operations.
+	 * 
+	 * @return this unit as a {@code LinearUnit}
+	 * @since 2019-10-16
+	 */
+	public LinearUnit asLinearUnit() {
+		return LinearUnit.valueOf(this.getBase(), 1);
+	}
+
 	@Override
 	public double convertFromBase(final double value) {
 		return value;
diff --git a/src/org/unitConverter/newUnits/LinearUnit.java b/src/org/unitConverter/newUnits/LinearUnit.java
new file mode 100644
index 0000000..5a589b7
--- /dev/null
+++ b/src/org/unitConverter/newUnits/LinearUnit.java
@@ -0,0 +1,261 @@
+/**
+ * Copyright (C) 2019 Adrien Hopkins
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+package org.unitConverter.newUnits;
+
+import java.util.Objects;
+
+import org.unitConverter.math.DecimalComparison;
+import org.unitConverter.math.ObjectProduct;
+
+/**
+ * A unit that can be expressed as a product of its base and a number. For example, kilometres, inches and pounds.
+ * 
+ * @author Adrien Hopkins
+ * @since 2019-10-16
+ */
+public final class LinearUnit extends AbstractUnit {
+	/**
+	 * Gets a {@code LinearUnit} from a unit base and a conversion factor. In other words, gets the product of
+	 * {@code unitBase} and {@code conversionFactor}, expressed as a {@code LinearUnit}.
+	 * 
+	 * @param unitBase
+	 *            unit base to multiply by
+	 * @param conversionFactor
+	 *            number to multiply base by
+	 * @return product of base and conversion factor
+	 * @since 2019-10-16
+	 */
+	public static LinearUnit valueOf(final ObjectProduct<BaseUnit> unitBase, final double conversionFactor) {
+		return new LinearUnit(unitBase, conversionFactor);
+	}
+
+	/**
+	 * The value of this unit as represented in its base form. Mathematically,
+	 * 
+	 * <pre>
+	 * this = conversionFactor * getBase()
+	 * </pre>
+	 * 
+	 * @since 2019-10-16
+	 */
+	private final double conversionFactor;
+
+	/**
+	 * Creates the {@code LinearUnit}.
+	 * 
+	 * @param unitBase
+	 *            base of linear unit
+	 * @param conversionFactor
+	 *            conversion factor between base and unit
+	 * @since 2019-10-16
+	 */
+	private LinearUnit(final ObjectProduct<BaseUnit> unitBase, final double conversionFactor) {
+		super(unitBase);
+		this.conversionFactor = conversionFactor;
+	}
+
+	@Override
+	public double convertFromBase(final double value) {
+		return value / this.getConversionFactor();
+	}
+
+	@Override
+	public double convertToBase(final double value) {
+		return value * this.getConversionFactor();
+	}
+
+	/**
+	 * Divides this unit by a scalar.
+	 * 
+	 * @param divisor
+	 *            scalar to divide by
+	 * @return quotient
+	 * @since 2018-12-23
+	 * @since v0.1.0
+	 */
+	public LinearUnit dividedBy(final double divisor) {
+		return valueOf(this.getBase(), this.getConversionFactor() / divisor);
+	}
+
+	/**
+	 * Returns the quotient of this unit and another.
+	 * 
+	 * @param divisor
+	 *            unit to divide by
+	 * @return quotient of two units
+	 * @throws NullPointerException
+	 *             if {@code divisor} is null
+	 * @since 2018-12-22
+	 * @since v0.1.0
+	 */
+	public LinearUnit dividedBy(final LinearUnit divisor) {
+		Objects.requireNonNull(divisor, "other must not be null");
+
+		// divide the units
+		final ObjectProduct<BaseUnit> base = this.getBase().dividedBy(divisor.getBase());
+		return valueOf(base, this.getConversionFactor() / divisor.getConversionFactor());
+	}
+
+	@Override
+	public boolean equals(final Object obj) {
+		if (!(obj instanceof LinearUnit))
+			return false;
+		final LinearUnit other = (LinearUnit) obj;
+		return Objects.equals(this.getBase(), other.getBase())
+				&& DecimalComparison.equals(this.getConversionFactor(), other.getConversionFactor());
+	}
+
+	/**
+	 * @return conversion factor
+	 * @since 2019-10-16
+	 */
+	public double getConversionFactor() {
+		return this.conversionFactor;
+	}
+
+	@Override
+	public int hashCode() {
+		return Objects.hash(this.getBase(), this.getConversionFactor());
+	}
+
+	/**
+	 * @return whether this unit is equivalent to a {@code BaseUnit} (i.e. there is a {@code BaseUnit b} where
+	 *         {@code b.asLinearUnit().equals(this)} returns {@code true}.)
+	 * @since 2019-10-16
+	 */
+	public boolean isBase() {
+		return this.isCoherent() && this.getBase().isSingleObject();
+	}
+
+	/**
+	 * @return whether this unit is coherent (i.e. has conversion factor 1)
+	 * @since 2019-10-16
+	 */
+	public boolean isCoherent() {
+		return this.getConversionFactor() == 1;
+	}
+
+	/**
+	 * Returns the difference of this unit and another.
+	 * <p>
+	 * Two units can be subtracted if they have the same base. If {@code subtrahend} does not meet this condition, an
+	 * {@code IllegalArgumentException} will be thrown.
+	 * </p>
+	 * 
+	 * @param subtrahend
+	 *            unit to subtract
+	 * @return difference of units
+	 * @throws IllegalArgumentException
+	 *             if {@code subtrahend} is not compatible for subtraction as described above
+	 * @throws NullPointerException
+	 *             if {@code subtrahend} is null
+	 * @since 2019-03-17
+	 * @since v0.2.0
+	 */
+	public LinearUnit minus(final LinearUnit subtrahendend) {
+		Objects.requireNonNull(subtrahendend, "addend must not be null.");
+
+		// reject subtrahends that cannot be added to this unit
+		if (!this.getBase().equals(subtrahendend.getBase()))
+			throw new IllegalArgumentException(
+					String.format("Incompatible units for subtraction \"%s\" and \"%s\".", this, subtrahendend));
+
+		// add the units
+		return valueOf(this.getBase(), this.getConversionFactor() - subtrahendend.getConversionFactor());
+	}
+
+	/**
+	 * Returns the sum of this unit and another.
+	 * <p>
+	 * Two units can be added if they have the same base. If {@code addend} does not meet this condition, an
+	 * {@code IllegalArgumentException} will be thrown.
+	 * </p>
+	 * 
+	 * @param addend
+	 *            unit to add
+	 * @return sum of units
+	 * @throws IllegalArgumentException
+	 *             if {@code addend} is not compatible for addition as described above
+	 * @throws NullPointerException
+	 *             if {@code addend} is null
+	 * @since 2019-03-17
+	 * @since v0.2.0
+	 */
+	public LinearUnit plus(final LinearUnit addend) {
+		Objects.requireNonNull(addend, "addend must not be null.");
+
+		// reject addends that cannot be added to this unit
+		if (!this.getBase().equals(addend.getBase()))
+			throw new IllegalArgumentException(
+					String.format("Incompatible units for addition \"%s\" and \"%s\".", this, addend));
+
+		// add the units
+		return valueOf(this.getBase(), this.getConversionFactor() + addend.getConversionFactor());
+	}
+
+	/**
+	 * Multiplies this unit by a scalar.
+	 * 
+	 * @param multiplier
+	 *            scalar to multiply by
+	 * @return product
+	 * @since 2018-12-23
+	 * @since v0.1.0
+	 */
+	public LinearUnit times(final double multiplier) {
+		return valueOf(this.getBase(), this.getConversionFactor() * multiplier);
+	}
+
+	/**
+	 * Returns the product of this unit and another.
+	 * 
+	 * @param multiplier
+	 *            unit to multiply by
+	 * @return product of two units
+	 * @throws NullPointerException
+	 *             if {@code multiplier} is null
+	 * @since 2018-12-22
+	 * @since v0.1.0
+	 */
+	public LinearUnit times(final LinearUnit multiplier) {
+		Objects.requireNonNull(multiplier, "other must not be null");
+
+		// multiply the units
+		final ObjectProduct<BaseUnit> base = this.getBase().times(multiplier.getBase());
+		return valueOf(base, this.getConversionFactor() * multiplier.getConversionFactor());
+	}
+
+	/**
+	 * Returns this unit but to an exponent.
+	 * 
+	 * @param exponent
+	 *            exponent to exponentiate unit to
+	 * @return exponentiated unit
+	 * @since 2019-01-15
+	 * @since v0.1.0
+	 */
+	public LinearUnit toExponent(final int exponent) {
+		return valueOf(this.getBase().toExponent(exponent), Math.pow(this.conversionFactor, exponent));
+	}
+
+	// returns a definition of the unit
+	@Override
+	public String toString() {
+		return Double.toString(this.conversionFactor) + " * " + this.getBase().toString(BaseUnit::getSymbol);
+	}
+
+}
diff --git a/src/org/unitConverter/newUnits/Unit.java b/src/org/unitConverter/newUnits/Unit.java
index 339afde..b50115d 100644
--- a/src/org/unitConverter/newUnits/Unit.java
+++ b/src/org/unitConverter/newUnits/Unit.java
@@ -23,6 +23,8 @@ import org.unitConverter.dimension.BaseDimension;
 import org.unitConverter.math.ObjectProduct;
 
 /**
+ * A unit described in terms of base units.
+ * 
  * @author Adrien Hopkins
  * @since 2019-10-16
  */