bundles/org.eclipse.osgi.util/src/org/osgi/util/measurement/Measurement.java - equinox/rt.equinox.framework - Git at Google

 /*
  * Copyright (c) OSGi Alliance (2002, 2016). All Rights Reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 package org.osgi.util.measurement;

 /**
  * Represents a value with an error, a unit and a time-stamp.
  *
  * <p>
  * A {@code Measurement} object is used for maintaining the tuple of value,
  * error, unit and time-stamp. The value and error are represented as doubles
  * and the time is measured in milliseconds since midnight, January 1, 1970 UTC.
  *
  * <p>
  * Mathematic methods are provided that correctly calculate taking the error
  * into account. A runtime error will occur when two measurements are used in an
  * incompatible way. E.g., when a speed (m/s) is added to a distance (m). The
  * measurement class will correctly track changes in unit during multiplication
  * and division, always coercing the result to the most simple form. See
  * {@link Unit} for more information on the supported units.
  *
  * <p>
  * Errors in the measurement class are absolute errors. Measurement errors
  * should use the P95 rule. Actual values must fall in the range value +/- error
  * 95% or more of the time.
  *
  * <p>
  * A {@code Measurement} object is immutable in order to be easily shared.
  *
  * <p>
  * Note: This class has a natural ordering that is inconsistent with equals. See
  * {@link #compareTo(Object)}.
  *
  * @Immutable
  * @author $Id$
  */
 public class Measurement implements Comparable<Object> {
 	private final double		value;
 	private final double		error;
 	private final long			time;
 	private final Unit			unit;
 	private transient String	name;
 	private transient int		hashCode;

 	/**
 	 * Create a new {@code Measurement} object.
 	 *
 	 * @param value The value of the {@code Measurement}.
 	 * @param error The error of the {@code Measurement}.
 	 * @param unit The {@code Unit} object in which the value is measured. If
 	 *        this argument is {@code null}, then the unit will be set to
 	 *        {@link Unit#unity}.
 	 * @param time The time measured in milliseconds since midnight, January 1,
 	 *        1970 UTC.
 	 */
 	public Measurement(double value, double error, Unit unit, long time) {
 		this.value = value;
 		this.error = Math.abs(error);
 		this.unit = (unit != null) ? unit : Unit.unity;
 		this.time = time;
 		name = null;
 		hashCode = 0;
 	}

 	/**
 	 * Create a new {@code Measurement} object with a time of zero.
 	 *
 	 * @param value The value of the {@code Measurement}.
 	 * @param error The error of the {@code Measurement}.
 	 * @param unit The {@code Unit} object in which the value is measured. If
 	 *        this argument is {@code null}, then the unit will be set to
 	 *        {@link Unit#unity}.
 	 */
 	public Measurement(double value, double error, Unit unit) {
 		this(value, error, unit, 0l);
 	}

 	/**
 	 * Create a new {@code Measurement} object with an error of 0.0 and a time
 	 * of zero.
 	 *
 	 * @param value The value of the {@code Measurement}.
 	 * @param unit The {@code Unit} in which the value is measured. If this
 	 *        argument is {@code null}, then the unit will be set to
 	 *        {@link Unit#unity}.
 	 */
 	public Measurement(double value, Unit unit) {
 		this(value, 0.0d, unit, 0l);
 	}

 	/**
 	 * Create a new {@code Measurement} object with an error of 0.0, a unit of
 	 * {@link Unit#unity} and a time of zero.
 	 *
 	 * @param value The value of the {@code Measurement}.
 	 */
 	public Measurement(double value) {
 		this(value, 0.0d, null, 0l);
 	}

 	/**
 	 * Returns the value of this {@code Measurement} object.
 	 *
 	 * @return The value of this {@code Measurement} object as a double.
 	 */
 	public final double getValue() {
 		return value;
 	}

 	/**
 	 * Returns the error of this {@code Measurement} object. The error is always
 	 * a positive value.
 	 *
 	 * @return The error of this {@code Measurement} as a double.
 	 */
 	public final double getError() {
 		return error;
 	}

 	/**
 	 * Returns the {@code Unit} object of this {@code Measurement} object.
 	 *
 	 * @return The {@code Unit} object of this {@code Measurement} object.
 	 *
 	 * @see Unit
 	 */
 	public final Unit getUnit() {
 		return unit;
 	}

 	/**
 	 * Returns the time at which this {@code Measurement} object was taken. The
 	 * time is measured in milliseconds since midnight, January 1, 1970 UTC, or
 	 * zero when not defined.
 	 *
 	 * @return The time at which this {@code Measurement} object was taken or
 	 *         zero.
 	 */
 	public final long getTime() {
 		return time;
 	}

 	/**
 	 * Returns a new {@code Measurement} object that is the product of this
 	 * object multiplied by the specified object.
 	 *
 	 * @param m The {@code Measurement} object that will be multiplied with this
 	 *        object.
 	 * @return A new {@code Measurement} that is the product of this object
 	 *         multiplied by the specified object. The error and unit of the new
 	 *         object are computed. The time of the new object is set to the
 	 *         time of this object.
 	 * @throws ArithmeticException If the {@code Unit} objects of this object
 	 *         and the specified object cannot be multiplied.
 	 * @see Unit
 	 */
 	public Measurement mul(Measurement m) {
 		double mvalue = m.value;
 		return new Measurement(value * mvalue, Math.abs(value) * m.error + error * Math.abs(mvalue), unit.mul(m.unit), time);
 	}

 	/**
 	 * Returns a new {@code Measurement} object that is the product of this
 	 * object multiplied by the specified value.
 	 *
 	 * @param d The value that will be multiplied with this object.
 	 * @param u The {@code Unit} of the specified value.
 	 * @return A new {@code Measurement} object that is the product of this
 	 *         object multiplied by the specified value. The error and unit of
 	 *         the new object are computed. The time of the new object is set to
 	 *         the time of this object.
 	 * @throws ArithmeticException If the units of this object and the specified
 	 *         value cannot be multiplied.
 	 * @see Unit
 	 */
 	public Measurement mul(double d, Unit u) {
 		return new Measurement(value * d, error * Math.abs(d), unit.mul(u), time);
 	}

 	/**
 	 * Returns a new {@code Measurement} object that is the product of this
 	 * object multiplied by the specified value.
 	 *
 	 * @param d The value that will be multiplied with this object.
 	 * @return A new {@code Measurement} object that is the product of this
 	 *         object multiplied by the specified value. The error of the new
 	 *         object is computed. The unit and time of the new object is set to
 	 *         the unit and time of this object.
 	 */
 	public Measurement mul(double d) {
 		return new Measurement(value * d, error * Math.abs(d), unit, time);
 	}

 	/**
 	 * Returns a new {@code Measurement} object that is the quotient of this
 	 * object divided by the specified object.
 	 *
 	 * @param m The {@code Measurement} object that will be the divisor of this
 	 *        object.
 	 * @return A new {@code Measurement} object that is the quotient of this
 	 *         object divided by the specified object. The error and unit of the
 	 *         new object are computed. The time of the new object is set to the
 	 *         time of this object.
 	 * @throws ArithmeticException If the {@code Unit} objects of this object
 	 *         and the specified object cannot be divided.
 	 * @see Unit
 	 */
 	public Measurement div(Measurement m) {
 		double mvalue = m.value;
 		return new Measurement(value / mvalue, (Math.abs(value) * m.error + error * Math.abs(mvalue)) / (mvalue * mvalue), unit.div(m.unit), time);
 	}

 	/**
 	 * Returns a new {@code Measurement} object that is the quotient of this
 	 * object divided by the specified value.
 	 *
 	 * @param d The value that will be the divisor of this object.
 	 * @param u The {@code Unit} object of the specified value.
 	 * @return A new {@code Measurement} that is the quotient of this object
 	 *         divided by the specified value. The error and unit of the new
 	 *         object are computed. The time of the new object is set to the
 	 *         time of this object.
 	 * @throws ArithmeticException If the {@code Unit} objects of this object
 	 *         and the specified object cannot be divided.
 	 * @see Unit
 	 */
 	public Measurement div(double d, Unit u) {
 		return new Measurement(value / d, error / Math.abs(d), unit.div(u), time);
 	}

 	/**
 	 * Returns a new {@code Measurement} object that is the quotient of this
 	 * object divided by the specified value.
 	 *
 	 * @param d The value that will be the divisor of this object.
 	 * @return A new {@code Measurement} object that is the quotient of this
 	 *         object divided by the specified value. The error of the new
 	 *         object is computed. The unit and time of the new object is set to
 	 *         the {@code Unit} and time of this object.
 	 */
 	public Measurement div(double d) {
 		return new Measurement(value / d, error / Math.abs(d), unit, time);
 	}

 	/**
 	 * Returns a new {@code Measurement} object that is the sum of this object
 	 * added to the specified object.
 	 *
 	 * The error and unit of the new object are computed. The time of the new
 	 * object is set to the time of this object.
 	 *
 	 * @param m The {@code Measurement} object that will be added with this
 	 *        object.
 	 * @return A new {@code Measurement} object that is the sum of this and m.
 	 * @see Unit
 	 * @throws ArithmeticException If the {@code Unit} objects of this object
 	 *         and the specified object cannot be added.
 	 */
 	public Measurement add(Measurement m) {
 		return new Measurement(value + m.value, error + m.error, unit.add(m.unit), time);
 	}

 	/**
 	 * Returns a new {@code Measurement} object that is the sum of this object
 	 * added to the specified value.
 	 *
 	 * @param d The value that will be added with this object.
 	 * @param u The {@code Unit} object of the specified value.
 	 * @return A new {@code Measurement} object that is the sum of this object
 	 *         added to the specified value. The unit of the new object is
 	 *         computed. The error and time of the new object is set to the
 	 *         error and time of this object.
 	 * @throws ArithmeticException If the {@code Unit} objects of this object
 	 *         and the specified value cannot be added.
 	 * @see Unit
 	 */
 	public Measurement add(double d, Unit u) {
 		return new Measurement(value + d, error, unit.add(u), time);
 	}

 	/**
 	 * Returns a new {@code Measurement} object that is the sum of this object
 	 * added to the specified value.
 	 *
 	 * @param d The value that will be added with this object.
 	 * @return A new {@code Measurement} object that is the sum of this object
 	 *         added to the specified value. The error, unit, and time of the
 	 *         new object is set to the error, {@code Unit} and time of this
 	 *         object.
 	 */
 	public Measurement add(double d) {
 		return new Measurement(value + d, error, unit, time);
 	}

 	/**
 	 * Returns a new {@code Measurement} object that is the subtraction of the
 	 * specified object from this object.
 	 *
 	 * @param m The {@code Measurement} object that will be subtracted from this
 	 *        object.
 	 * @return A new {@code Measurement} object that is the subtraction of the
 	 *         specified object from this object. The error and unit of the new
 	 *         object are computed. The time of the new object is set to the
 	 *         time of this object.
 	 * @throws ArithmeticException If the {@code Unit} objects of this object
 	 *         and the specified object cannot be subtracted.
 	 * @see Unit
 	 */
 	public Measurement sub(Measurement m) {
 		return new Measurement(value - m.value, error + m.error, unit.sub(m.unit), time);
 	}

 	/**
 	 * Returns a new {@code Measurement} object that is the subtraction of the
 	 * specified value from this object.
 	 *
 	 * @param d The value that will be subtracted from this object.
 	 * @param u The {@code Unit} object of the specified value.
 	 * @return A new {@code Measurement} object that is the subtraction of the
 	 *         specified value from this object. The unit of the new object is
 	 *         computed. The error and time of the new object is set to the
 	 *         error and time of this object.
 	 * @throws ArithmeticException If the {@code Unit} objects of this object
 	 *         and the specified object cannot be subtracted.
 	 * @see Unit
 	 */
 	public Measurement sub(double d, Unit u) {
 		return new Measurement(value - d, error, unit.sub(u), time);
 	}

 	/**
 	 * Returns a new {@code Measurement} object that is the subtraction of the
 	 * specified value from this object.
 	 *
 	 * @param d The value that will be subtracted from this object.
 	 * @return A new {@code Measurement} object that is the subtraction of the
 	 *         specified value from this object. The error, unit and time of the
 	 *         new object is set to the error, {@code Unit} object and time of
 	 *         this object.
 	 */
 	public Measurement sub(double d) {
 		return new Measurement(value - d, error, unit, time);
 	}

 	/**
 	 * Returns a {@code String} object representing this {@code Measurement}
 	 * object.
 	 *
 	 * @return a {@code String} object representing this {@code Measurement}
 	 *         object.
 	 */
 	@Override
 	public String toString() {
 		String result = name;
 		if (result == null) {
 			StringBuilder sb = new StringBuilder();
 			sb.append(value);
 			if (error != 0.0d) {
 				sb.append(" +/- ");
 				sb.append(error);
 			}
 			String u = unit.toString();
 			if (u.length() > 0) {
 				sb.append(" ");
 				sb.append(u);
 			}
 			result = sb.toString();
 			name = result;
 		}
 		return result;
 	}

 	/**
 	 * Compares this object with the specified object for order. Returns a
 	 * negative integer, zero, or a positive integer if this object is less
 	 * than, equal to, or greater than the specified object.
 	 *
 	 * <p>
 	 * Note: This class has a natural ordering that is inconsistent with equals.
 	 * For this method, another {@code Measurement} object is considered equal
 	 * if there is some {@code x} such that
 	 *
 	 * <pre>
 	 * getValue() - getError() &lt;= x &lt;= getValue() + getError()
 	 * </pre>
 	 *
 	 * for both {@code Measurement} objects being compared.
 	 *
 	 * @param obj The object to be compared.
 	 * @return A negative integer, zero, or a positive integer if this object is
 	 *         less than, equal to, or greater than the specified object.
 	 *
 	 * @throws ClassCastException If the specified object is not of type
 	 *         {@code Measurement}.
 	 * @throws ArithmeticException If the unit of the specified
 	 *         {@code Measurement} object is not equal to the {@code Unit}
 	 *         object of this object.
 	 */
 	@Override
 	public int compareTo(Object obj) {
 		if (this == obj) {
 			return 0;
 		}
 		Measurement that = (Measurement) obj;
 		if (!unit.equals(that.unit)) {
 			throw new ArithmeticException("Cannot compare " + this + " and " + that);
 		}
 		int result = Double.compare(value, that.value);
 		if (result == 0) {
 			return 0;
 		}
 		if (result < 0) {
 			if (Double.compare(value + error, that.value - that.error) >= 0) {
 				return 0;
 			}
 			return -1;
 		}
 		if (Double.compare(value - error, that.value + that.error) <= 0) {
 			return 0;
 		}
 		return 1;
 	}

 	/**
 	 * Returns a hash code value for this object.
 	 *
 	 * @return A hash code value for this object.
 	 */
 	@Override
 	public int hashCode() {
 		int h = hashCode;
 		if (h == 0) {
 			long bits = Double.doubleToLongBits(value);
 			h = 31 * 17 + ((int) (bits ^ (bits >>> 32)));
 			bits = Double.doubleToLongBits(error);
 			h = 31 * h + ((int) (bits ^ (bits >>> 32)));
 			h = 31 * h + unit.hashCode();
 			hashCode = h;
 		}
 		return h;
 	}

 	/**
 	 * Returns whether the specified object is equal to this object. Two
 	 * {@code Measurement} objects are equal if they have same value, error and
 	 * {@code Unit}.
 	 *
 	 * <p>
 	 * Note: This class has a natural ordering that is inconsistent with equals.
 	 * See {@link #compareTo(Object)}.
 	 *
 	 * @param obj The object to compare with this object.
 	 * @return {@code true} if this object is equal to the specified object;
 	 *         {@code false} otherwise.
 	 */
 	@Override
 	public boolean equals(Object obj) {
 		if (this == obj) {
 			return true;
 		}
 		if (!(obj instanceof Measurement)) {
 			return false;
 		}
 		Measurement that = (Measurement) obj;
 		return (Double.compare(value, that.value) == 0) && (Double.compare(error, that.error) == 0) && unit.equals(that.unit);
 	}
 }
	/*
	* Copyright (c) OSGi Alliance (2002, 2016). All Rights Reserved.
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	package org.osgi.util.measurement;

	/**
	* Represents a value with an error, a unit and a time-stamp.
	*
	* <p>
	* A {@code Measurement} object is used for maintaining the tuple of value,
	* error, unit and time-stamp. The value and error are represented as doubles
	* and the time is measured in milliseconds since midnight, January 1, 1970 UTC.
	*
	* <p>
	* Mathematic methods are provided that correctly calculate taking the error
	* into account. A runtime error will occur when two measurements are used in an
	* incompatible way. E.g., when a speed (m/s) is added to a distance (m). The
	* measurement class will correctly track changes in unit during multiplication
	* and division, always coercing the result to the most simple form. See
	* {@link Unit} for more information on the supported units.
	*
	* <p>
	* Errors in the measurement class are absolute errors. Measurement errors
	* should use the P95 rule. Actual values must fall in the range value +/- error
	* 95% or more of the time.
	*
	* <p>
	* A {@code Measurement} object is immutable in order to be easily shared.
	*
	* <p>
	* Note: This class has a natural ordering that is inconsistent with equals. See
	* {@link #compareTo(Object)}.
	*
	* @Immutable
	* @author $Id$
	*/
	public class Measurement implements Comparable<Object> {
	private final double value;
	private final double error;
	private final long time;
	private final Unit unit;
	private transient String name;
	private transient int hashCode;

	/**
	* Create a new {@code Measurement} object.
	*
	* @param value The value of the {@code Measurement}.
	* @param error The error of the {@code Measurement}.
	* @param unit The {@code Unit} object in which the value is measured. If
	* this argument is {@code null}, then the unit will be set to
	* {@link Unit#unity}.
	* @param time The time measured in milliseconds since midnight, January 1,
	* 1970 UTC.
	*/
	public Measurement(double value, double error, Unit unit, long time) {
	this.value = value;
	this.error = Math.abs(error);
	this.unit = (unit != null) ? unit : Unit.unity;
	this.time = time;
	name = null;
	hashCode = 0;
	}

	/**
	* Create a new {@code Measurement} object with a time of zero.
	*
	* @param value The value of the {@code Measurement}.
	* @param error The error of the {@code Measurement}.
	* @param unit The {@code Unit} object in which the value is measured. If
	* this argument is {@code null}, then the unit will be set to
	* {@link Unit#unity}.
	*/
	public Measurement(double value, double error, Unit unit) {
	this(value, error, unit, 0l);
	}

	/**
	* Create a new {@code Measurement} object with an error of 0.0 and a time
	* of zero.
	*
	* @param value The value of the {@code Measurement}.
	* @param unit The {@code Unit} in which the value is measured. If this
	* argument is {@code null}, then the unit will be set to
	* {@link Unit#unity}.
	*/
	public Measurement(double value, Unit unit) {
	this(value, 0.0d, unit, 0l);
	}

	/**
	* Create a new {@code Measurement} object with an error of 0.0, a unit of
	* {@link Unit#unity} and a time of zero.
	*
	* @param value The value of the {@code Measurement}.
	*/
	public Measurement(double value) {
	this(value, 0.0d, null, 0l);
	}

	/**
	* Returns the value of this {@code Measurement} object.
	*
	* @return The value of this {@code Measurement} object as a double.
	*/
	public final double getValue() {
	return value;
	}

	/**
	* Returns the error of this {@code Measurement} object. The error is always
	* a positive value.
	*
	* @return The error of this {@code Measurement} as a double.
	*/
	public final double getError() {
	return error;
	}

	/**
	* Returns the {@code Unit} object of this {@code Measurement} object.
	*
	* @return The {@code Unit} object of this {@code Measurement} object.
	*
	* @see Unit
	*/
	public final Unit getUnit() {
	return unit;
	}

	/**
	* Returns the time at which this {@code Measurement} object was taken. The
	* time is measured in milliseconds since midnight, January 1, 1970 UTC, or
	* zero when not defined.
	*
	* @return The time at which this {@code Measurement} object was taken or
	* zero.
	*/
	public final long getTime() {
	return time;
	}

	/**
	* Returns a new {@code Measurement} object that is the product of this
	* object multiplied by the specified object.
	*
	* @param m The {@code Measurement} object that will be multiplied with this
	* object.
	* @return A new {@code Measurement} that is the product of this object
	* multiplied by the specified object. The error and unit of the new
	* object are computed. The time of the new object is set to the
	* time of this object.
	* @throws ArithmeticException If the {@code Unit} objects of this object
	* and the specified object cannot be multiplied.
	* @see Unit
	*/
	public Measurement mul(Measurement m) {
	double mvalue = m.value;
	return new Measurement(value * mvalue, Math.abs(value) * m.error + error * Math.abs(mvalue), unit.mul(m.unit), time);
	}

	/**
	* Returns a new {@code Measurement} object that is the product of this
	* object multiplied by the specified value.
	*
	* @param d The value that will be multiplied with this object.
	* @param u The {@code Unit} of the specified value.
	* @return A new {@code Measurement} object that is the product of this
	* object multiplied by the specified value. The error and unit of
	* the new object are computed. The time of the new object is set to
	* the time of this object.
	* @throws ArithmeticException If the units of this object and the specified
	* value cannot be multiplied.
	* @see Unit
	*/
	public Measurement mul(double d, Unit u) {
	return new Measurement(value * d, error * Math.abs(d), unit.mul(u), time);
	}

	/**
	* Returns a new {@code Measurement} object that is the product of this
	* object multiplied by the specified value.
	*
	* @param d The value that will be multiplied with this object.
	* @return A new {@code Measurement} object that is the product of this
	* object multiplied by the specified value. The error of the new
	* object is computed. The unit and time of the new object is set to
	* the unit and time of this object.
	*/
	public Measurement mul(double d) {
	return new Measurement(value * d, error * Math.abs(d), unit, time);
	}

	/**
	* Returns a new {@code Measurement} object that is the quotient of this
	* object divided by the specified object.
	*
	* @param m The {@code Measurement} object that will be the divisor of this
	* object.
	* @return A new {@code Measurement} object that is the quotient of this
	* object divided by the specified object. The error and unit of the
	* new object are computed. The time of the new object is set to the
	* time of this object.
	* @throws ArithmeticException If the {@code Unit} objects of this object
	* and the specified object cannot be divided.
	* @see Unit
	*/
	public Measurement div(Measurement m) {
	double mvalue = m.value;
	return new Measurement(value / mvalue, (Math.abs(value) * m.error + error * Math.abs(mvalue)) / (mvalue * mvalue), unit.div(m.unit), time);
	}

	/**
	* Returns a new {@code Measurement} object that is the quotient of this
	* object divided by the specified value.
	*
	* @param d The value that will be the divisor of this object.
	* @param u The {@code Unit} object of the specified value.
	* @return A new {@code Measurement} that is the quotient of this object
	* divided by the specified value. The error and unit of the new
	* object are computed. The time of the new object is set to the
	* time of this object.
	* @throws ArithmeticException If the {@code Unit} objects of this object
	* and the specified object cannot be divided.
	* @see Unit
	*/
	public Measurement div(double d, Unit u) {
	return new Measurement(value / d, error / Math.abs(d), unit.div(u), time);
	}

	/**
	* Returns a new {@code Measurement} object that is the quotient of this
	* object divided by the specified value.
	*
	* @param d The value that will be the divisor of this object.
	* @return A new {@code Measurement} object that is the quotient of this
	* object divided by the specified value. The error of the new
	* object is computed. The unit and time of the new object is set to
	* the {@code Unit} and time of this object.
	*/
	public Measurement div(double d) {
	return new Measurement(value / d, error / Math.abs(d), unit, time);
	}

	/**
	* Returns a new {@code Measurement} object that is the sum of this object
	* added to the specified object.
	*
	* The error and unit of the new object are computed. The time of the new
	* object is set to the time of this object.
	*
	* @param m The {@code Measurement} object that will be added with this
	* object.
	* @return A new {@code Measurement} object that is the sum of this and m.
	* @see Unit
	* @throws ArithmeticException If the {@code Unit} objects of this object
	* and the specified object cannot be added.
	*/
	public Measurement add(Measurement m) {
	return new Measurement(value + m.value, error + m.error, unit.add(m.unit), time);
	}

	/**
	* Returns a new {@code Measurement} object that is the sum of this object
	* added to the specified value.
	*
	* @param d The value that will be added with this object.
	* @param u The {@code Unit} object of the specified value.
	* @return A new {@code Measurement} object that is the sum of this object
	* added to the specified value. The unit of the new object is
	* computed. The error and time of the new object is set to the
	* error and time of this object.
	* @throws ArithmeticException If the {@code Unit} objects of this object
	* and the specified value cannot be added.
	* @see Unit
	*/
	public Measurement add(double d, Unit u) {
	return new Measurement(value + d, error, unit.add(u), time);
	}

	/**
	* Returns a new {@code Measurement} object that is the sum of this object
	* added to the specified value.
	*
	* @param d The value that will be added with this object.
	* @return A new {@code Measurement} object that is the sum of this object
	* added to the specified value. The error, unit, and time of the
	* new object is set to the error, {@code Unit} and time of this
	* object.
	*/
	public Measurement add(double d) {
	return new Measurement(value + d, error, unit, time);
	}

	/**
	* Returns a new {@code Measurement} object that is the subtraction of the
	* specified object from this object.
	*
	* @param m The {@code Measurement} object that will be subtracted from this
	* object.
	* @return A new {@code Measurement} object that is the subtraction of the
	* specified object from this object. The error and unit of the new
	* object are computed. The time of the new object is set to the
	* time of this object.
	* @throws ArithmeticException If the {@code Unit} objects of this object
	* and the specified object cannot be subtracted.
	* @see Unit
	*/
	public Measurement sub(Measurement m) {
	return new Measurement(value - m.value, error + m.error, unit.sub(m.unit), time);
	}

	/**
	* Returns a new {@code Measurement} object that is the subtraction of the
	* specified value from this object.
	*
	* @param d The value that will be subtracted from this object.
	* @param u The {@code Unit} object of the specified value.
	* @return A new {@code Measurement} object that is the subtraction of the
	* specified value from this object. The unit of the new object is
	* computed. The error and time of the new object is set to the
	* error and time of this object.
	* @throws ArithmeticException If the {@code Unit} objects of this object
	* and the specified object cannot be subtracted.
	* @see Unit
	*/
	public Measurement sub(double d, Unit u) {
	return new Measurement(value - d, error, unit.sub(u), time);
	}

	/**
	* Returns a new {@code Measurement} object that is the subtraction of the
	* specified value from this object.
	*
	* @param d The value that will be subtracted from this object.
	* @return A new {@code Measurement} object that is the subtraction of the
	* specified value from this object. The error, unit and time of the
	* new object is set to the error, {@code Unit} object and time of
	* this object.
	*/
	public Measurement sub(double d) {
	return new Measurement(value - d, error, unit, time);
	}

	/**
	* Returns a {@code String} object representing this {@code Measurement}
	* object.
	*
	* @return a {@code String} object representing this {@code Measurement}
	* object.
	*/
	@Override
	public String toString() {
	String result = name;
	if (result == null) {
	StringBuilder sb = new StringBuilder();
	sb.append(value);
	if (error != 0.0d) {
	sb.append(" +/- ");
	sb.append(error);
	}
	String u = unit.toString();
	if (u.length() > 0) {
	sb.append(" ");
	sb.append(u);
	}
	result = sb.toString();
	name = result;
	}
	return result;
	}

	/**
	* Compares this object with the specified object for order. Returns a
	* negative integer, zero, or a positive integer if this object is less
	* than, equal to, or greater than the specified object.
	*
	* <p>
	* Note: This class has a natural ordering that is inconsistent with equals.
	* For this method, another {@code Measurement} object is considered equal
	* if there is some {@code x} such that
	*
	* <pre>
	* getValue() - getError() <= x <= getValue() + getError()
	* </pre>
	*
	* for both {@code Measurement} objects being compared.
	*
	* @param obj The object to be compared.
	* @return A negative integer, zero, or a positive integer if this object is
	* less than, equal to, or greater than the specified object.
	*
	* @throws ClassCastException If the specified object is not of type
	* {@code Measurement}.
	* @throws ArithmeticException If the unit of the specified
	* {@code Measurement} object is not equal to the {@code Unit}
	* object of this object.
	*/
	@Override
	public int compareTo(Object obj) {
	if (this == obj) {
	return 0;
	}
	Measurement that = (Measurement) obj;
	if (!unit.equals(that.unit)) {
	throw new ArithmeticException("Cannot compare " + this + " and " + that);
	}
	int result = Double.compare(value, that.value);
	if (result == 0) {
	return 0;
	}
	if (result < 0) {
	if (Double.compare(value + error, that.value - that.error) >= 0) {
	return 0;
	}
	return -1;
	}
	if (Double.compare(value - error, that.value + that.error) <= 0) {
	return 0;
	}
	return 1;
	}

	/**
	* Returns a hash code value for this object.
	*
	* @return A hash code value for this object.
	*/
	@Override
	public int hashCode() {
	int h = hashCode;
	if (h == 0) {
	long bits = Double.doubleToLongBits(value);
	h = 31 * 17 + ((int) (bits ^ (bits >>> 32)));
	bits = Double.doubleToLongBits(error);
	h = 31 * h + ((int) (bits ^ (bits >>> 32)));
	h = 31 * h + unit.hashCode();
	hashCode = h;
	}
	return h;
	}

	/**
	* Returns whether the specified object is equal to this object. Two
	* {@code Measurement} objects are equal if they have same value, error and
	* {@code Unit}.
	*
	* <p>
	* Note: This class has a natural ordering that is inconsistent with equals.
	* See {@link #compareTo(Object)}.
	*
	* @param obj The object to compare with this object.
	* @return {@code true} if this object is equal to the specified object;
	* {@code false} otherwise.
	*/
	@Override
	public boolean equals(Object obj) {
	if (this == obj) {
	return true;
	}
	if (!(obj instanceof Measurement)) {
	return false;
	}
	Measurement that = (Measurement) obj;
	return (Double.compare(value, that.value) == 0) && (Double.compare(error, that.error) == 0) && unit.equals(that.unit);
	}
	}