11 files changed, 899 insertions, 2 deletions
diff --git a/src/unitConverter/unit/AbstractUnit.java b/src/unitConverter/unit/AbstractUnit.java
new file mode 100644
index 0000000..24814e8
--- /dev/null
+++ b/src/unitConverter/unit/AbstractUnit.java
@@ -0,0 +1,172 @@
+/**
+ * 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 unitConverter.unit;
+
+import java.util.Objects;
+
+import unitConverter.dimension.UnitDimension;
+
+/**
+ * The default abstract implementation of the {@code Unit} interface.
+ * 
+ * @author Adrien Hopkins
+ * @since 2018-12-22
+ * @since v0.1.0
+ */
+public abstract class AbstractUnit implements Unit {
+	/**
+	 * The number of units created, including base units.
+	 * 
+	 * @since 2019-01-02
+	 * @since v0.1.0
+	 */
+	private static long unitCount = 0;
+
+	/**
+	 * The number of base units created.
+	 * 
+	 * @since 2019-01-02
+	 * @since v0.1.0
+	 */
+	private static long baseUnitCount = 0;
+
+	/**
+	 * @return number of base units created
+	 * @since 2019-01-02
+	 * @since v0.1.0
+	 */
+	public static final long getBaseUnitCount() {
+		return baseUnitCount;
+	}
+
+	/**
+	 * @return number of units created
+	 * @since 2019-01-02
+	 * @since v0.1.0
+	 */
+	public static final long getUnitCount() {
+		return unitCount;
+	}
+
+	/**
+	 * Increments the number of base units.
+	 * 
+	 * @since 2019-01-15
+	 * @since v0.1.0
+	 */
+	public static final void incrementBaseUnitCounter() {
+		baseUnitCount++;
+	}
+
+	/**
+	 * Increments the number of units.
+	 * 
+	 * @since 2019-01-15
+	 * @since v0.1.0
+	 */
+	public static final void incrementUnitCounter() {
+		unitCount++;
+	}
+
+	/**
+	 * The dimension, or what the unit measures.
+	 * 
+	 * @since 2018-12-22
+	 * @since v0.1.0
+	 */
+	private final UnitDimension dimension;
+
+	/**
+	 * The unit's base unit. Values converted by {@code convertFromBase} and {@code convertToBase} are expressed in this
+	 * unit.
+	 * 
+	 * @since 2018-12-22
+	 * @since v0.1.0
+	 */
+	private final BaseUnit base;
+
+	/**
+	 * The system that this unit is a part of.
+	 * 
+	 * @since 2018-12-23
+	 * @since v0.1.0
+	 */
+	private final UnitSystem system;
+
+	/**
+	 * Creates the {@code AbstractUnit}.
+	 * 
+	 * @param base
+	 *            unit's base
+	 * @throws NullPointerException
+	 *             if name, symbol or base is null
+	 * @since 2018-12-22
+	 * @since v0.1.0
+	 */
+	public AbstractUnit(final BaseUnit base) {
+		this.base = Objects.requireNonNull(base, "base must not be null.");
+		this.dimension = this.base.getDimension();
+		this.system = this.base.getSystem();
+	}
+
+	/**
+	 * Creates the {@code AbstractUnit} using a unique dimension. This constructor is for making base units and should
+	 * only be used by {@code BaseUnit}.
+	 * 
+	 * @param dimension
+	 *            dimension measured by unit
+	 * @param system
+	 *            system that unit is a part of
+	 * @throws AssertionError
+	 *             if this constructor is not run by {@code BaseUnit} or a subclass
+	 * @throws NullPointerException
+	 *             if name, symbol or dimension is null
+	 * @since 2018-12-23
+	 * @since v0.1.0
+	 */
+	AbstractUnit(final UnitDimension dimension, final UnitSystem system) {
+		// try to set this as a base unit
+		if (this instanceof BaseUnit) {
+			this.base = (BaseUnit) this;
+		} else
+			throw new AssertionError();
+
+		this.dimension = Objects.requireNonNull(dimension, "dimension must not be null.");
+		this.system = Objects.requireNonNull(system, "system must not be null.");
+	}
+
+	@Override
+	public final BaseUnit getBase() {
+		return this.base;
+	}
+
+	@Override
+	public final UnitDimension getDimension() {
+		return this.dimension;
+	}
+
+	@Override
+	public final UnitSystem getSystem() {
+		return this.system;
+	}
+
+	// TODO document and revise units' toString methods
+	@Override
+	public String toString() {
+		return String.format("%s-derived unit of dimension %s", this.getSystem(), this.getDimension());
+	}
+}
diff --git a/src/unitConverter/unit/BaseUnit.java b/src/unitConverter/unit/BaseUnit.java
new file mode 100755
index 0000000..fe36c45
--- /dev/null
+++ b/src/unitConverter/unit/BaseUnit.java
@@ -0,0 +1,180 @@
+/**
+ * Copyright (C) 2018 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 unitConverter.unit;
+
+import java.util.Objects;
+
+import unitConverter.dimension.UnitDimension;
+
+/**
+ * A unit that is the base for its dimension. It does not have to be for a base dimension, so units like the Newton and
+ * Joule are still base units.
+ * 
+ * @author Adrien Hopkins
+ * @since 2018-12-23
+ * @since v0.1.0
+ */
+public final class BaseUnit extends AbstractUnit {
+	/**
+	 * Is this unit a full base (i.e. m, s, ... but not N, J, ...)
+	 * 
+	 * @since 2019-01-15
+	 * @since v0.1.0
+	 */
+	private final boolean isFullBase;
+
+	/**
+	 * Creates the {@code BaseUnit}.
+	 * 
+	 * @param dimension
+	 *            dimension measured by unit
+	 * @param system
+	 *            system that unit is a part of
+	 * @param name
+	 *            name of unit
+	 * @param symbol
+	 *            symbol of unit
+	 * @since 2018-12-23
+	 * @since v0.1.0
+	 */
+	BaseUnit(final UnitDimension dimension, final UnitSystem system) {
+		super(dimension, system);
+		this.isFullBase = dimension.isBase();
+	}
+
+	/**
+	 * @return this unit as a {@code LinearUnit}
+	 * @since 2019-01-25
+	 * @since v0.1.0
+	 */
+	public LinearUnit asLinearUnit() {
+		return this.times(1);
+	}
+
+	@Override
+	public double convertFromBase(final double value) {
+		return value;
+	}
+
+	@Override
+	public double convertToBase(final double value) {
+		return value;
+	}
+
+	/**
+	 * Divides this unit by another unit.
+	 * 
+	 * @param other
+	 *            unit to divide by
+	 * @return quotient of two units
+	 * @throws IllegalArgumentException
+	 *             if this unit's system is not other's system
+	 * @throws NullPointerException
+	 *             if other is null
+	 * @since 2018-12-22
+	 * @since v0.1.0
+	 */
+	public BaseUnit dividedBy(final BaseUnit other) {
+		Objects.requireNonNull(other, "other must not be null.");
+		if (!this.getSystem().equals(other.getSystem()))
+			throw new IllegalArgumentException("Incompatible base units for division.");
+		return new BaseUnit(this.getDimension().dividedBy(other.getDimension()), this.getSystem());
+	}
+
+	/**
+	 * Divides this unit by a divisor
+	 * 
+	 * @param divisor
+	 *            amount to divide by
+	 * @return quotient
+	 * @since 2018-12-23
+	 * @since v0.1.0
+	 */
+	public LinearUnit dividedBy(final double divisor) {
+		return new LinearUnit(this, 1 / divisor);
+	}
+
+	@Override
+	public boolean equals(final Object obj) {
+		if (!(obj instanceof BaseUnit))
+			return false;
+		final BaseUnit other = (BaseUnit) obj;
+		return Objects.equals(this.getSystem(), other.getSystem())
+				&& Objects.equals(this.getDimension(), other.getDimension());
+	}
+
+	@Override
+	public int hashCode() {
+		final int prime = 31;
+		int result = 1;
+		result = result * prime + this.getSystem().hashCode();
+		result = result * prime + this.getDimension().hashCode();
+		return result;
+	}
+
+	/**
+	 * Multiplies this unit by another unit.
+	 * 
+	 * @param other
+	 *            unit to multiply by
+	 * @return product of two units
+	 * @throws IllegalArgumentException
+	 *             if this unit's system is not other's system
+	 * @throws NullPointerException
+	 *             if other is null
+	 * @since 2018-12-22
+	 * @since v0.1.0
+	 */
+	public BaseUnit times(final BaseUnit other) {
+		Objects.requireNonNull(other, "other must not be null.");
+		if (!this.getSystem().equals(other.getSystem()))
+			throw new IllegalArgumentException("Incompatible base units for multiplication.");
+		return new BaseUnit(this.getDimension().times(other.getDimension()), this.getSystem());
+	}
+
+	/**
+	 * Multiplies this unit by a multiplier.
+	 * 
+	 * @param multiplier
+	 *            amount to multiply by
+	 * @return product
+	 * @since 2018-12-23
+	 * @since v0.1.0
+	 */
+	public LinearUnit times(final double multiplier) {
+		return new LinearUnit(this, multiplier);
+	}
+
+	/**
+	 * Returns this unit, but to an exponent.
+	 * 
+	 * @param exponent
+	 *            exponent
+	 * @return result of exponentiation
+	 * @since 2019-01-15
+	 * @since v0.1.0
+	 */
+	public BaseUnit toExponent(final int exponent) {
+		return this.getSystem().getBaseUnit(this.getDimension().toExponent(exponent));
+	}
+
+	@Override
+	public String toString() {
+		return String.format("%s base unit of%s dimension %s", this.getSystem(), this.isFullBase ? " base" : "",
+				this.getDimension());
+	}
+}
diff --git a/src/unitConverter/unit/DefaultUnitPrefix.java b/src/unitConverter/unit/DefaultUnitPrefix.java
new file mode 100755
index 0000000..d19161b
--- /dev/null
+++ b/src/unitConverter/unit/DefaultUnitPrefix.java
@@ -0,0 +1,67 @@
+/**
+ * Copyright (C) 2018 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 unitConverter.unit;
+
+import java.util.Objects;
+
+/**
+ * The default implementation of {@code UnitPrefix}, which contains a multiplier and nothing else.
+ * 
+ * @author Adrien Hopkins
+ * @since 2019-01-14
+ * @since v0.1.0
+ */
+public final class DefaultUnitPrefix implements UnitPrefix {
+	private final double multiplier;
+
+	/**
+	 * Creates the {@code DefaultUnitPrefix}.
+	 * 
+	 * @param multiplier
+	 * @since 2019-01-14
+	 */
+	public DefaultUnitPrefix(final double multiplier) {
+		this.multiplier = multiplier;
+	}
+
+	@Override
+	public boolean equals(final Object obj) {
+		if (this == obj)
+			return true;
+		if (obj == null)
+			return false;
+		if (!(obj instanceof DefaultUnitPrefix))
+			return false;
+		final DefaultUnitPrefix other = (DefaultUnitPrefix) obj;
+		return Double.doubleToLongBits(this.multiplier) == Double.doubleToLongBits(other.multiplier);
+	}
+
+	@Override
+	public double getMultiplier() {
+		return this.multiplier;
+	}
+
+	@Override
+	public int hashCode() {
+		return Objects.hash(this.multiplier);
+	}
+
+	@Override
+	public String toString() {
+		return String.format("Unit prefix equal to %s", this.multiplier);
+	}
+}
diff --git a/src/unitConverter/unit/LinearUnit.java b/src/unitConverter/unit/LinearUnit.java
new file mode 100644
index 0000000..b786b3b
--- /dev/null
+++ b/src/unitConverter/unit/LinearUnit.java
@@ -0,0 +1,184 @@
+/**
+ * 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 unitConverter.unit;
+
+import java.util.Objects;
+
+import unitConverter.dimension.UnitDimension;
+
+/**
+ * A unit that is equal to a certain number multiplied by its base.
+ * 
+ * @author Adrien Hopkins
+ * @since 2018-12-22
+ * @since v0.1.0
+ */
+public final class LinearUnit extends AbstractUnit {
+	/**
+	 * The value of one of this unit in this unit's base unit
+	 * 
+	 * @since 2018-12-22
+	 * @since v0.1.0
+	 */
+	private final double conversionFactor;
+
+	/**
+	 * 
+	 * Creates the {@code LinearUnit}.
+	 * 
+	 * @param base
+	 *            unit's base
+	 * @param conversionFactor
+	 *            value of one of this unit in its base
+	 * @since 2018-12-23
+	 * @since v0.1.0
+	 */
+	LinearUnit(final BaseUnit base, final double conversionFactor) {
+		super(base);
+		this.conversionFactor = conversionFactor;
+	}
+
+	/**
+	 * Creates the {@code LinearUnit} as a base unit.
+	 * 
+	 * @param dimension
+	 *            dimension measured by unit
+	 * @param system
+	 *            system unit is part of
+	 * @since 2019-01-25
+	 * @since v0.1.0
+	 */
+	LinearUnit(final UnitDimension dimension, final UnitSystem system, final double conversionFactor) {
+		super(dimension, system);
+		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 new LinearUnit(this.getBase(), this.getConversionFactor() / divisor);
+	}
+
+	/**
+	 * Divides this unit by another unit.
+	 * 
+	 * @param other
+	 *            unit to divide by
+	 * @return quotient of two units
+	 * @throws NullPointerException
+	 *             if other is null
+	 * @since 2018-12-22
+	 * @since v0.1.0
+	 */
+	public LinearUnit dividedBy(final LinearUnit other) {
+		Objects.requireNonNull(other, "other must not be null");
+		final BaseUnit base = this.getBase().dividedBy(other.getBase());
+		return new LinearUnit(base, this.getConversionFactor() / other.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())
+				&& Objects.equals(this.getConversionFactor(), other.getConversionFactor());
+	}
+
+	/**
+	 * @return conversionFactor
+	 * @since 2018-12-22
+	 * @since v0.1.0
+	 */
+	public final double getConversionFactor() {
+		return this.conversionFactor;
+	}
+
+	@Override
+	public int hashCode() {
+		final int prime = 31;
+		int result = 1;
+		result = result * prime + this.getBase().hashCode();
+		result = result * prime + Double.hashCode(this.getConversionFactor());
+		return result;
+	}
+
+	/**
+	 * 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 new LinearUnit(this.getBase(), this.getConversionFactor() * multiplier);
+	}
+
+	/**
+	 * Multiplies this unit by another unit.
+	 * 
+	 * @param other
+	 *            unit to multiply by=
+	 * @return product of two units
+	 * @throws NullPointerException
+	 *             if other is null
+	 * @since 2018-12-22
+	 * @since v0.1.0
+	 */
+	public LinearUnit times(final LinearUnit other) {
+		Objects.requireNonNull(other, "other must not be null");
+		final BaseUnit base = this.getBase().times(other.getBase());
+		return new LinearUnit(base, this.getConversionFactor() * other.getConversionFactor());
+	}
+
+	/**
+	 * Returns this unit but to an exponent.
+	 * 
+	 * @param exponent
+	 *            exponent to exponientate unit to
+	 * @return exponientated unit
+	 * @since 2019-01-15
+	 * @since v0.1.0
+	 */
+	public LinearUnit toExponent(final int exponent) {
+		return new LinearUnit(this.getBase().toExponent(exponent), Math.pow(this.conversionFactor, exponent));
+	}
+
+	@Override
+	public String toString() {
+		return super.toString() + String.format(" (equal to %s * base)", this.getConversionFactor());
+	}
+}
diff --git a/src/unitConverter/unit/NonlinearUnits.java b/src/unitConverter/unit/NonlinearUnits.java
new file mode 100755
index 0000000..ec1874c
--- /dev/null
+++ b/src/unitConverter/unit/NonlinearUnits.java
@@ -0,0 +1,57 @@
+/**
+ * Copyright (C) 2018 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 unitConverter.unit;
+
+/**
+ * Some major nonlinear units.
+ * 
+ * @author Adrien Hopkins
+ * @since 2019-01-14
+ * @since v0.1.0
+ */
+public final class NonlinearUnits {
+	public static final Unit CELSIUS = new AbstractUnit(SI.KELVIN) {
+
+		@Override
+		public double convertFromBase(final double value) {
+			return value - 273.15;
+		}
+
+		@Override
+		public double convertToBase(final double value) {
+			return value + 273.15;
+		}
+	};
+
+	public static final Unit FAHRENHEIT = new AbstractUnit(SI.KELVIN) {
+
+		@Override
+		public double convertFromBase(final double value) {
+			return 1.8 * value - 459.67;
+		}
+
+		@Override
+		public double convertToBase(final double value) {
+			return (value + 459.67) / 1.8;
+		}
+	};
+
+	// You may NOT get a NonlinearUnits instance.
+	private NonlinearUnits() {
+		throw new AssertionError();
+	}
+}
diff --git a/src/unitConverter/unit/SI.java b/src/unitConverter/unit/SI.java
new file mode 100644
index 0000000..54eb4c5
--- /dev/null
+++ b/src/unitConverter/unit/SI.java
@@ -0,0 +1,74 @@
+/**
+ * Copyright (C) 2018 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 unitConverter.unit;
+
+import java.util.HashSet;
+import java.util.Objects;
+import java.util.Set;
+
+import unitConverter.dimension.StandardDimensions;
+import unitConverter.dimension.UnitDimension;
+
+/**
+ * The SI, which holds all SI units
+ * 
+ * @author Adrien Hopkins
+ * @since 2018-12-23
+ * @since v0.1.0
+ */
+public enum SI implements UnitSystem {
+	SI;
+
+	/**
+	 * This system's base units.
+	 * 
+	 * @since 2019-01-25
+	 * @since v0.1.0
+	 */
+	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);
+	public static final BaseUnit SECOND = SI.getBaseUnit(StandardDimensions.TIME);
+	public static final BaseUnit AMPERE = SI.getBaseUnit(StandardDimensions.ELECTRIC_CURRENT);
+	public static final BaseUnit KELVIN = SI.getBaseUnit(StandardDimensions.TEMPERATURE);
+	public static final BaseUnit MOLE = SI.getBaseUnit(StandardDimensions.QUANTITY);
+	public static final BaseUnit CANDELA = SI.getBaseUnit(StandardDimensions.LUMINOUS_INTENSITY);
+
+	@Override
+	public BaseUnit getBaseUnit(final UnitDimension dimension) {
+		// 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
+	public String getName() {
+		return "SI";
+	}
+}
diff --git a/src/unitConverter/unit/SIPrefix.java b/src/unitConverter/unit/SIPrefix.java
new file mode 100755
index 0000000..54625fb
--- /dev/null
+++ b/src/unitConverter/unit/SIPrefix.java
@@ -0,0 +1,54 @@
+/**
+ * Copyright (C) 2018 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 unitConverter.unit;
+
+/**
+ * The SI prefixes.
+ * 
+ * @author Adrien Hopkins
+ * @since 2019-01-14
+ * @since v0.1.0
+ */
+public enum SIPrefix implements UnitPrefix {
+	DECA(10), HECTO(100), KILO(1e3), MEGA(1e6), GIGA(1e9), TERA(1e12), PETA(1e15), EXA(1e18), ZETTA(1e21), YOTTA(
+			1e24), DECI(0.1), CENTI(0.01), MILLI(
+					1e-3), MICRO(1e-6), NANO(1e-9), PICO(1e-12), FEMTO(1e-15), ATTO(1e-18), ZEPTO(1e-21), YOCTO(1e-24);
+
+	private final double multiplier;
+
+	/**
+	 * Creates the {@code SIPrefix}.
+	 * 
+	 * @param multiplier
+	 *            prefix's multiplier
+	 * @since 2019-01-14
+	 * @since v0.1.0
+	 */
+	private SIPrefix(final double multiplier) {
+		this.multiplier = multiplier;
+	}
+
+	/**
+	 * @return value
+	 * @since 2019-01-14
+	 * @since v0.1.0
+	 */
+	@Override
+	public final double getMultiplier() {
+		return this.multiplier;
+	}
+}
diff --git a/src/unitConverter/unit/Unit.java b/src/unitConverter/unit/Unit.java
index 3e7f9da..54f1423 100755
--- a/src/unitConverter/unit/Unit.java
+++ b/src/unitConverter/unit/Unit.java
@@ -25,6 +25,7 @@ import unitConverter.dimension.UnitDimension;
  * 
  * @author Adrien Hopkins
  * @since 2018-12-22
+ * @since v0.1.0
  */
 public interface Unit {
 	/**
@@ -34,6 +35,7 @@ public interface Unit {
 	 *            unit to test with
 	 * @return true if the units are compatible
 	 * @since 2019-01-13
+	 * @since v0.1.0
 	 */
 	default boolean canConvertTo(final Unit other) {
 		return Objects.equals(this.getBase(), other.getBase());
@@ -53,6 +55,7 @@ public interface Unit {
 	 *            value expressed in <b>base</b> unit
 	 * @return value expressed in <b>this</b> unit
 	 * @since 2018-12-22
+	 * @since v0.1.0
 	 */
 	double convertFromBase(double value);
 
@@ -70,6 +73,7 @@ public interface Unit {
 	 *            value expressed in <b>this</b> unit
 	 * @return value expressed in <b>base</b> unit
 	 * @since 2018-12-22
+	 * @since v0.1.0
 	 */
 	double convertToBase(double value);
 
@@ -86,18 +90,21 @@ public interface Unit {
 	 * 
 	 * @return base unit associated with this unit
 	 * @since 2018-12-22
+	 * @since v0.1.0
 	 */
-	Unit getBase();
+	BaseUnit getBase();
 
 	/**
 	 * @return dimension measured by this unit
 	 * @since 2018-12-22
+	 * @since v0.1.0
 	 */
 	UnitDimension getDimension();
 
 	/**
 	 * @return system that this unit is a part of
 	 * @since 2018-12-23
+	 * @since v0.1.0
 	 */
 	UnitSystem getSystem();
 }
diff --git a/src/unitConverter/unit/UnitPrefix.java b/src/unitConverter/unit/UnitPrefix.java
new file mode 100755
index 0000000..a0c1b7c
--- /dev/null
+++ b/src/unitConverter/unit/UnitPrefix.java
@@ -0,0 +1,33 @@
+/**
+ * Copyright (C) 2018 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 unitConverter.unit;
+
+/**
+ * A prefix that can be attached onto the front of any unit, which multiplies it by a certain value
+ * 
+ * @author Adrien Hopkins
+ * @since 2019-01-14
+ * @since v0.1.0
+ */
+public interface UnitPrefix {
+	/**
+	 * @return this prefix's multiplier
+	 * @since 2019-01-14
+	 * @since v0.1.0
+	 */
+	double getMultiplier();
+}
diff --git a/src/unitConverter/unit/UnitSystem.java b/src/unitConverter/unit/UnitSystem.java
index 2e3a5d8..ce8c249 100755
--- a/src/unitConverter/unit/UnitSystem.java
+++ b/src/unitConverter/unit/UnitSystem.java
@@ -16,16 +16,38 @@
  */
 package unitConverter.unit;
 
+import java.util.Objects;
+
+import unitConverter.dimension.UnitDimension;
+
 /**
  * A system of units. Each unit should be aware of its system.
  * 
  * @author Adrien Hopkins
  * @since 2018-12-23
+ * @since v0.1.0
  */
 public interface UnitSystem {
 	/**
-	 * @return name of system
+	 * Gets a base unit for this system and the provided dimension.
+	 * 
+	 * @param dimension
+	 *            dimension used by base unit
+	 * @return base unit
+	 * @throws NullPointerException
+	 *             if dimension is null
 	 * @since 2019-01-25
+	 * @since v0.1.0
+	 */
+	default BaseUnit getBaseUnit(final UnitDimension dimension) {
+		Objects.requireNonNull(dimension, "dimension must not be null.");
+		return new BaseUnit(dimension, this);
+	}
+
+	/**
+	 * @return name of system
+	 * @since 2018-12-23
+	 * @since v0.1.0
 	 */
 	String getName();
 }
diff --git a/src/unitConverter/unit/UnitTest.java b/src/unitConverter/unit/UnitTest.java
new file mode 100755
index 0000000..c3237eb
--- /dev/null
+++ b/src/unitConverter/unit/UnitTest.java
@@ -0,0 +1,47 @@
+/**
+ * Copyright (C) 2018 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 unitConverter.unit;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+import unitConverter.dimension.StandardDimensions;
+
+/**
+ * Testing the various Unit classes
+ * 
+ * @author Adrien Hopkins
+ * @since 2018-12-22
+ */
+class UnitTest {
+	@Test
+	void testConversion() {
+		final BaseUnit metre = SI.METRE;
+		final Unit inch = metre.times(0.0254);
+
+		assertEquals(1.9, inch.convertToBase(75), 0.01);
+	}
+
+	@Test
+	void testEquals() {
+		final BaseUnit metre = SI.METRE;
+		final Unit meter = SI.SI.getBaseUnit(StandardDimensions.LENGTH);
+
+		assertEquals(metre, meter);
+	}
+}