| 1 | /* |
| 2 | * JScience - Java(TM) Tools and Libraries for the Advancement of Sciences. |
| 3 | * Copyright (C) 2006 - JScience (http://jscience.org/) |
| 4 | * All rights reserved. |
| 5 | * |
| 6 | * Permission to use, copy, modify, and distribute this software is |
| 7 | * freely granted, provided that this notice is preserved. |
| 8 | */ |
| 9 | package javax.measure.unit; |
| 10 | |
| 11 | import java.io.Serializable; |
| 12 | import java.text.ParseException; |
| 13 | import java.text.ParsePosition; |
| 14 | import java.util.HashMap; |
| 15 | |
| 16 | import javax.measure.MeasureFormat; |
| 17 | import javax.measure.converter.AddConverter; |
| 18 | import javax.measure.converter.ConversionException; |
| 19 | import javax.measure.converter.MultiplyConverter; |
| 20 | import javax.measure.converter.RationalConverter; |
| 21 | import javax.measure.converter.UnitConverter; |
| 22 | import javax.measure.quantity.Dimensionless; |
| 23 | import javax.measure.quantity.Quantity; |
| 24 | |
| 25 | /** |
| 26 | * <p> This class represents a determinate {@link javax.measure.quantity.Quantity |
| 27 | * quantity} (as of length, time, heat, or value) adopted as a standard |
| 28 | * of measurement.</p> |
| 29 | * |
| 30 | * <p> It is helpful to think of instances of this class as recording the |
| 31 | * history by which they are created. Thus, for example, the string |
| 32 | * "g/kg" (which is a dimensionless unit) would result from invoking |
| 33 | * the method toString() on a unit that was created by dividing a |
| 34 | * gram unit by a kilogram unit. Yet, "kg" divided by "kg" returns |
| 35 | * {@link #ONE} and not "kg/kg" due to automatic unit factorization.</p> |
| 36 | * |
| 37 | * <p> This class supports the multiplication of offsets units. The result is |
| 38 | * usually a unit not convertible to its {@link #getStandardUnit standard unit}. |
| 39 | * Such units may appear in derivative quantities. For example °C/m is an |
| 40 | * unit of gradient, which is common in atmospheric and oceanographic |
| 41 | * research.</p> |
| 42 | * |
| 43 | * <p> Units raised at rational powers are also supported. For example |
| 44 | * the cubic root of "liter" is a unit compatible with meter.</p> |
| 45 | * |
| 46 | * <p> Instances of this class are immutable.</p> |
| 47 | * |
| 48 | * @author <a href="mailto:jean-marie@dautelle.com">Jean-Marie Dautelle</a> |
| 49 | * @author <a href="mailto:steve@unidata.ucar.edu">Steve Emmerson</a> |
| 50 | * @author Martin Desruisseaux |
| 51 | * @version 3.2, August 28, 2006 |
| 52 | * @see <a href="http://en.wikipedia.org/wiki/Units_of_measurement"> |
| 53 | * Wikipedia: Units of measurement</a> |
| 54 | */ |
| 55 | public abstract class Unit<Q extends Quantity> implements Serializable { |
| 56 | |
| 57 | /** |
| 58 | * Holds the dimensionless unit <code>ONE</code>. |
| 59 | */ |
| 60 | public static final Unit<Dimensionless> ONE = new ProductUnit<Dimensionless>(); |
| 61 | |
| 62 | /** |
| 63 | * Holds the unique symbols collection (base unit or alternate units). |
| 64 | */ |
| 65 | static final HashMap<String, Unit<?>> SYMBOL_TO_UNIT = new HashMap<String, Unit<?>>(); |
| 66 | |
| 67 | /** |
| 68 | * Default constructor. |
| 69 | */ |
| 70 | protected Unit() { |
| 71 | } |
| 72 | |
| 73 | ////////////////////////////////////////////////////// |
| 74 | // Contract methods (for sub-classes to implement). // |
| 75 | ////////////////////////////////////////////////////// |
| 76 | |
| 77 | /** |
| 78 | * Returns the {@link BaseUnit base unit}, {@link AlternateUnit alternate |
| 79 | * unit} or product of base units and alternate units this unit is derived |
| 80 | * from. The standard unit identifies the "type" of |
| 81 | * {@link javax.measure.quantity.Quantity quantity} for which this unit is employed. |
| 82 | * For example:[code] |
| 83 | * boolean isAngularVelocity(Unit<?> u) { |
| 84 | * return u.getStandardUnit().equals(RADIAN.divide(SECOND)); |
| 85 | * } |
| 86 | * assert(REVOLUTION.divide(MINUTE).isAngularVelocity()); |
| 87 | * [/code] |
| 88 | * |
| 89 | * <p><i> Note: Having the same system unit is not sufficient to ensure |
| 90 | * that a converter exists between the two units |
| 91 | * (e.g. °C/m and K/m).</i></p> |
| 92 | * @return the system unit this unit is derived from. |
| 93 | */ |
| 94 | public abstract Unit<? super Q> getStandardUnit(); |
| 95 | |
| 96 | |
| 97 | /** |
| 98 | * Returns the converter from this unit to its system unit. |
| 99 | * |
| 100 | * @return <code>this.getConverterTo(this.getSystemUnit())</code> |
| 101 | */ |
| 102 | public abstract UnitConverter toStandardUnit(); |
| 103 | |
| 104 | /** |
| 105 | * Returns the hash code for this unit. |
| 106 | * |
| 107 | * @return this unit hashcode value. |
| 108 | */ |
| 109 | public abstract int hashCode(); |
| 110 | |
| 111 | /** |
| 112 | * Indicates if the specified unit can be considered equals to |
| 113 | * the one specified. |
| 114 | * |
| 115 | * @param that the object to compare to. |
| 116 | * @return <code>true</code> if this unit is considered equal to |
| 117 | * that unit; <code>false</code> otherwise. |
| 118 | */ |
| 119 | public abstract boolean equals(Object that); |
| 120 | |
| 121 | /** |
| 122 | * Indicates if this unit is a standard unit (base units and |
| 123 | * alternate units are standard units). The standard unit identifies |
| 124 | * the "type" of {@link javax.measure.quantity.Quantity quantity} for |
| 125 | * which the unit is employed. |
| 126 | * |
| 127 | * @return <code>getStandardUnit().equals(this)</code> |
| 128 | */ |
| 129 | public boolean isStandardUnit() { |
| 130 | return getStandardUnit().equals(this); |
| 131 | } |
| 132 | |
| 133 | /** |
| 134 | * Indicates if this unit is compatible with the unit specified. |
| 135 | * Units don't need to be equals to be compatible. For example:[code] |
| 136 | * RADIAN.equals(ONE) == false |
| 137 | * RADIAN.isCompatible(ONE) == true |
| 138 | * [/code] |
| 139 | * @param that the other unit. |
| 140 | * @return <code>this.getDimension().equals(that.getDimension())</code> |
| 141 | * @see #getDimension() |
| 142 | */ |
| 143 | public final boolean isCompatible(Unit<?> that) { |
| 144 | return (this == that) |
| 145 | || this.getStandardUnit().equals(that.getStandardUnit()) |
| 146 | || this.getDimension().equals(that.getDimension()); |
| 147 | } |
| 148 | |
| 149 | /** |
| 150 | * Casts this unit to a parameterized unit of specified nature or |
| 151 | * throw a <code>ClassCastException</code> if the dimension of the |
| 152 | * specified quantity and this unit's dimension do not match. |
| 153 | * For example:[code] |
| 154 | * Unit<Length> LIGHT_YEAR = NonSI.C.times(NonSI.YEAR).asType(Length.class); |
| 155 | * [/code] |
| 156 | * |
| 157 | * @param type the quantity class identifying the nature of the unit. |
| 158 | * @return this unit parameterized with the specified type. |
| 159 | * @throws ClassCastException if the dimension of this unit is different |
| 160 | * from the specified quantity dimension. |
| 161 | * @throws UnsupportedOperationException if the specified quantity class |
| 162 | * does not have a public static field named "UNIT" holding the |
| 163 | * standard unit for the quantity. |
| 164 | */ |
| 165 | @SuppressWarnings("unchecked") |
| 166 | public final <T extends Quantity> Unit<T> asType(Class<T> type) throws ClassCastException { |
| 167 | Dimension dim1 = this.getDimension(); |
| 168 | Unit<T> u = null; |
| 169 | try { |
| 170 | u = (Unit<T>)type.getField("UNIT").get(null); |
| 171 | } catch (Exception e) { |
| 172 | throw new Error(e); |
| 173 | } |
| 174 | Dimension dim2 = u.getDimension(); |
| 175 | if (!dim1.equals(dim2)) |
| 176 | throw new ClassCastException(); |
| 177 | return (Unit<T>)this; |
| 178 | } |
| 179 | |
| 180 | /** |
| 181 | * Returns the dimension of this unit (depends upon the current |
| 182 | * dimensional {@link Dimension.Model model}). |
| 183 | * |
| 184 | * @return the dimension of this unit for the current model. |
| 185 | */ |
| 186 | public final Dimension getDimension() { |
| 187 | Unit<?> systemUnit = this.getStandardUnit(); |
| 188 | if (systemUnit instanceof BaseUnit) |
| 189 | return Dimension.getModel().getDimension((BaseUnit<?>) systemUnit); |
| 190 | if (systemUnit instanceof AlternateUnit) |
| 191 | return ((AlternateUnit<?>) systemUnit).getParent().getDimension(); |
| 192 | // Product of units. |
| 193 | ProductUnit<?> productUnit = (ProductUnit<?>) systemUnit; |
| 194 | Dimension dimension = Dimension.NONE; |
| 195 | for (int i = 0; i < productUnit.getUnitCount(); i++) { |
| 196 | Unit<?> unit = productUnit.getUnit(i); |
| 197 | Dimension d = unit.getDimension().pow(productUnit.getUnitPow(i)) |
| 198 | .root(productUnit.getUnitRoot(i)); |
| 199 | dimension = dimension.times(d); |
| 200 | } |
| 201 | return dimension; |
| 202 | } |
| 203 | |
| 204 | /** |
| 205 | * Returns a converter of numeric values from this unit to another unit. |
| 206 | * |
| 207 | * @param that the unit to which to convert the numeric values. |
| 208 | * @return the converter from this unit to <code>that</code> unit. |
| 209 | * @throws ConversionException if the conveter cannot be constructed |
| 210 | * (e.g. <code>!this.isCompatible(that)</code>). |
| 211 | */ |
| 212 | public final UnitConverter getConverterTo(Unit<?> that) |
| 213 | throws ConversionException { |
| 214 | if (this.equals(that)) |
| 215 | return UnitConverter.IDENTITY; |
| 216 | Unit<?> thisSystemUnit = this.getStandardUnit(); |
| 217 | Unit<?> thatSystemUnit = that.getStandardUnit(); |
| 218 | if (thisSystemUnit.equals(thatSystemUnit)) |
| 219 | return that.toStandardUnit().inverse().concatenate( |
| 220 | this.toStandardUnit()); |
| 221 | // Use dimensional transforms. |
| 222 | if (!thisSystemUnit.getDimension() |
| 223 | .equals(thatSystemUnit.getDimension())) |
| 224 | throw new ConversionException(this + " is not compatible with " |
| 225 | + that); |
| 226 | // Transform between SystemUnit and BaseUnits is Identity. |
| 227 | UnitConverter thisTransform = this.toStandardUnit().concatenate( |
| 228 | transformOf(this.getBaseUnits())); |
| 229 | UnitConverter thatTransform = that.toStandardUnit().concatenate( |
| 230 | transformOf(that.getBaseUnits())); |
| 231 | return thatTransform.inverse().concatenate(thisTransform); |
| 232 | } |
| 233 | |
| 234 | private Unit<?> getBaseUnits() { |
| 235 | Unit<?> systemUnit = this.getStandardUnit(); |
| 236 | if (systemUnit instanceof BaseUnit) return systemUnit; |
| 237 | if (systemUnit instanceof AlternateUnit) |
| 238 | return ((AlternateUnit<?>)systemUnit).getParent().getBaseUnits(); |
| 239 | if (systemUnit instanceof ProductUnit) { |
| 240 | ProductUnit<?> productUnit = (ProductUnit<?>)systemUnit; |
| 241 | Unit<?> baseUnits = ONE; |
| 242 | for (int i = 0; i < productUnit.getUnitCount(); i++) { |
| 243 | Unit<?> unit = productUnit.getUnit(i).getBaseUnits(); |
| 244 | unit = unit.pow(productUnit.getUnitPow(i)); |
| 245 | unit = unit.root(productUnit.getUnitRoot(i)); |
| 246 | baseUnits = baseUnits.times(unit); |
| 247 | } |
| 248 | return baseUnits; |
| 249 | } else { |
| 250 | throw new InternalError( |
| 251 | "System Unit cannot be an instance of " + this.getClass()); |
| 252 | } |
| 253 | } |
| 254 | private static UnitConverter transformOf(Unit<?> baseUnits) { |
| 255 | if (baseUnits instanceof BaseUnit) |
| 256 | return Dimension.getModel().getTransform((BaseUnit<?>) baseUnits); |
| 257 | // Product of units. |
| 258 | ProductUnit<?> productUnit = (ProductUnit<?>) baseUnits; |
| 259 | UnitConverter converter = UnitConverter.IDENTITY; |
| 260 | for (int i = 0; i < productUnit.getUnitCount(); i++) { |
| 261 | Unit<?> unit = productUnit.getUnit(i); |
| 262 | UnitConverter cvtr = transformOf(unit); |
| 263 | if (!cvtr.isLinear()) |
| 264 | throw new ConversionException(baseUnits |
| 265 | + " is non-linear, cannot convert"); |
| 266 | if (productUnit.getUnitRoot(i) != 1) |
| 267 | throw new ConversionException(productUnit |
| 268 | + " holds a base unit with fractional exponent"); |
| 269 | int pow = productUnit.getUnitPow(i); |
| 270 | if (pow < 0) { // Negative power. |
| 271 | pow = -pow; |
| 272 | cvtr = cvtr.inverse(); |
| 273 | } |
| 274 | for (int j = 0; j < pow; j++) { |
| 275 | converter = converter.concatenate(cvtr); |
| 276 | } |
| 277 | } |
| 278 | return converter; |
| 279 | } |
| 280 | |
| 281 | /** |
| 282 | * Returns a unit equivalent to this unit but used in expressions to |
| 283 | * distinguish between quantities of a different nature but of the same |
| 284 | * dimensions. |
| 285 | * |
| 286 | * <p> Examples of alternate units:[code] |
| 287 | * Unit<Angle> RADIAN = ONE.alternate("rad"); |
| 288 | * Unit<Force> NEWTON = METER.times(KILOGRAM).divide(SECOND.pow(2)).alternate("N"); |
| 289 | * Unit<Pressure> PASCAL = NEWTON.divide(METER.pow(2)).alternate("Pa"); |
| 290 | * [/code]</p> |
| 291 | * |
| 292 | * @param symbol the new symbol for the alternate unit. |
| 293 | * @return the alternate unit. |
| 294 | * @throws UnsupportedOperationException if this unit is not a standard unit. |
| 295 | * @throws IllegalArgumentException if the specified symbol is already |
| 296 | * associated to a different unit. |
| 297 | */ |
| 298 | public final <A extends Quantity> AlternateUnit<A> alternate(String symbol) { |
| 299 | return new AlternateUnit<A>(symbol, this); |
| 300 | } |
| 301 | |
| 302 | /** |
| 303 | * Returns the combination of this unit with the specified sub-unit. |
| 304 | * Compound units are typically used for formatting purpose. |
| 305 | * Examples of compound units:[code] |
| 306 | * HOUR_MINUTE = NonSI.HOUR.compound(NonSI.MINUTE); |
| 307 | * DEGREE_MINUTE_SECOND_ANGLE = NonSI.DEGREE_ANGLE.compound( |
| 308 | * NonSI.DEGREE_MINUTE).compound(NonSI.SECOND_ANGLE); |
| 309 | * [/code] |
| 310 | * |
| 311 | * @param subunit the sub-unit to combine with this unit. |
| 312 | * @return the corresponding compound unit. |
| 313 | */ |
| 314 | public final CompoundUnit<Q> compound(Unit<Q> subunit) { |
| 315 | return new CompoundUnit<Q>(this, subunit); |
| 316 | } |
| 317 | |
| 318 | /** |
| 319 | * Returns the unit derived from this unit using the specified converter. |
| 320 | * The converter does not need to be linear. For example:[code] |
| 321 | * Unit<Dimensionless> DECIBEL = Unit.ONE.transform( |
| 322 | * new LogConverter(10).inverse().concatenate( |
| 323 | * new RationalConverter(1, 10)));[/code] |
| 324 | * |
| 325 | * @param operation the converter from the transformed unit to this unit. |
| 326 | * @return the unit after the specified transformation. |
| 327 | */ |
| 328 | public final Unit<Q> transform(UnitConverter operation) { |
| 329 | if (this instanceof TransformedUnit) { |
| 330 | TransformedUnit<Q> tf = (TransformedUnit<Q>) this; |
| 331 | Unit<Q> parent = tf.getParentUnit(); |
| 332 | UnitConverter toParent = tf.toParentUnit().concatenate(operation); |
| 333 | if (toParent == UnitConverter.IDENTITY) |
| 334 | return parent; |
| 335 | return new TransformedUnit<Q>(parent, toParent); |
| 336 | } |
| 337 | if (operation == UnitConverter.IDENTITY) |
| 338 | return this; |
| 339 | return new TransformedUnit<Q>(this, operation); |
| 340 | } |
| 341 | |
| 342 | /** |
| 343 | * Returns the result of adding an offset to this unit. The returned unit |
| 344 | * is convertible with all units that are convertible with this unit. |
| 345 | * |
| 346 | * @param offset the offset added (expressed in this unit, |
| 347 | * e.g. <code>CELSIUS = KELVIN.plus(273.15)</code>). |
| 348 | * @return <code>this.transform(new AddConverter(offset))</code> |
| 349 | */ |
| 350 | public final Unit<Q> plus(double offset) { |
| 351 | return transform(new AddConverter(offset)); |
| 352 | } |
| 353 | |
| 354 | /** |
| 355 | * Returns the result of multiplying this unit by an exact factor. |
| 356 | * |
| 357 | * @param factor the exact scale factor |
| 358 | * (e.g. <code>KILOMETER = METER.times(1000)</code>). |
| 359 | * @return <code>this.transform(new RationalConverter(factor, 1))</code> |
| 360 | */ |
| 361 | public final Unit<Q> times(long factor) { |
| 362 | return transform(new RationalConverter(factor, 1)); |
| 363 | } |
| 364 | |
| 365 | /** |
| 366 | * Returns the result of multiplying this unit by a an approximate factor |
| 367 | * |
| 368 | * @param factor the approximate factor (e.g. |
| 369 | * <code>ELECTRON_MASS = KILOGRAM.times(9.10938188e-31)</code>). |
| 370 | * @return <code>this.transform(new MultiplyConverter(factor))</code> |
| 371 | */ |
| 372 | public final Unit<Q> times(double factor) { |
| 373 | return transform(new MultiplyConverter(factor)); |
| 374 | } |
| 375 | |
| 376 | /** |
| 377 | * Returns the product of this unit with the one specified. |
| 378 | * |
| 379 | * @param that the unit multiplicand. |
| 380 | * @return <code>this * that</code> |
| 381 | */ |
| 382 | public final Unit<? extends Quantity> times(Unit<?> that) { |
| 383 | return ProductUnit.getProductInstance(this, that); |
| 384 | } |
| 385 | |
| 386 | /** |
| 387 | * Returns the inverse of this unit. |
| 388 | * |
| 389 | * @return <code>1 / this</code> |
| 390 | */ |
| 391 | public final Unit<? extends Quantity> inverse() { |
| 392 | return ProductUnit.getQuotientInstance(ONE, this); |
| 393 | } |
| 394 | |
| 395 | /** |
| 396 | * Returns the result of dividing this unit by an exact divisor. |
| 397 | * |
| 398 | * @param divisor the exact divisor. |
| 399 | * (e.g. <code>QUART = GALLON_LIQUID_US.divide(4)</code>). |
| 400 | * @return <code>this.transform(new RationalConverter(1 , divisor))</code> |
| 401 | */ |
| 402 | public final Unit<Q> divide(long divisor) { |
| 403 | return transform(new RationalConverter(1, divisor)); |
| 404 | } |
| 405 | |
| 406 | /** |
| 407 | * Returns the result of dividing this unit by an approximate divisor. |
| 408 | * |
| 409 | * @param divisor the approximate divisor. |
| 410 | * @return <code>this.transform(new MultiplyConverter(1.0 / divisor))</code> |
| 411 | */ |
| 412 | public final Unit<Q> divide(double divisor) { |
| 413 | return transform(new MultiplyConverter(1.0 / divisor)); |
| 414 | } |
| 415 | |
| 416 | /** |
| 417 | * Returns the quotient of this unit with the one specified. |
| 418 | * |
| 419 | * @param that the unit divisor. |
| 420 | * @return <code>this / that</code> |
| 421 | */ |
| 422 | public final Unit<? extends Quantity> divide(Unit<?> that) { |
| 423 | return this.times(that.inverse()); |
| 424 | } |
| 425 | |
| 426 | /** |
| 427 | * Returns a unit equals to the given root of this unit. |
| 428 | * |
| 429 | * @param n the root's order. |
| 430 | * @return the result of taking the given root of this unit. |
| 431 | * @throws ArithmeticException if <code>n == 0</code>. |
| 432 | */ |
| 433 | public final Unit<? extends Quantity> root(int n) { |
| 434 | if (n > 0) { |
| 435 | return ProductUnit.getRootInstance(this, n); |
| 436 | } else if (n == 0) { |
| 437 | throw new ArithmeticException("Root's order of zero"); |
| 438 | } else { // n < 0 |
| 439 | return ONE.divide(this.root(-n)); |
| 440 | } |
| 441 | } |
| 442 | |
| 443 | /** |
| 444 | * Returns a unit equals to this unit raised to an exponent. |
| 445 | * |
| 446 | * @param n the exponent. |
| 447 | * @return the result of raising this unit to the exponent. |
| 448 | */ |
| 449 | public final Unit<? extends Quantity> pow(int n) { |
| 450 | if (n > 0) { |
| 451 | return this.times(this.pow(n - 1)); |
| 452 | } else if (n == 0) { |
| 453 | return ONE; |
| 454 | } else { // n < 0 |
| 455 | return ONE.divide(this.pow(-n)); |
| 456 | } |
| 457 | } |
| 458 | |
| 459 | /** |
| 460 | * Returns a unit instance that is defined from the specified |
| 461 | * character sequence using the {@link UnitFormat#getInstance() |
| 462 | * standard unit format}. |
| 463 | * <p> Examples of valid entries (all for meters per second squared) are: |
| 464 | * <code><ul> |
| 465 | * <li>m*s-2</li> |
| 466 | * <li>m/s²</li> |
| 467 | * <li>m·s-²</li> |
| 468 | * <li>m*s**-2</li> |
| 469 | * <li>m^+1 s^-2</li> |
| 470 | * </ul></code></p> |
| 471 | * |
| 472 | * @param csq the character sequence to parse. |
| 473 | * @return <code>UnitFormat.getStandardInstance().parse(csq, new ParsePosition(0))</code> |
| 474 | * @throws IllegalArgumentException if the specified character sequence |
| 475 | * cannot be correctly parsed (e.g. symbol unknown). |
| 476 | */ |
| 477 | public static Unit<? extends Quantity> valueOf(CharSequence csq) { |
| 478 | try { |
| 479 | return UnitFormat.getInstance() |
| 480 | .parseProductUnit(csq, new ParsePosition(0)); |
| 481 | } catch (ParseException e) { |
| 482 | throw new IllegalArgumentException(e); |
| 483 | } |
| 484 | } |
| 485 | |
| 486 | ////////////////////// |
| 487 | // GENERAL CONTRACT // |
| 488 | ////////////////////// |
| 489 | |
| 490 | /** |
| 491 | * Returns the standard <code>String</code> representation of this unit. |
| 492 | * This representation is not affected by locale. Locale-sensitive |
| 493 | * unit formatting and parsing is handled by the {@link MeasureFormat} |
| 494 | * class and its subclasses. |
| 495 | * |
| 496 | * @return <code>UnitFormat.getStandardInstance().format(this)</code> |
| 497 | */ |
| 498 | public final String toString() { |
| 499 | return UnitFormat.getInstance().format(this); |
| 500 | } |
| 501 | } |