Package uk.me.nxg.unity

Class SimpleUnit

java.lang.Object
uk.me.nxg.unity.OneUnit
uk.me.nxg.unity.SimpleUnit
All Implemented Interfaces:
Comparable<OneUnit>
Direct Known Subclasses:
SimpleBinaryUnit, SimpleDecimalUnit
public abstract class SimpleUnit extends OneUnit
A single simple unit, such as 'kg'. This is represented as a prefix, a base unit and an exponent. For example, the string "mm s^-2" will result in two SimpleUnit instances, one of which will have a base unit of "m" and a prefix power of -3, and the other of which will have a base unit of "s" and an exponent of -2.

This represents the abstract unit, shorn of the symbols which were parsed to obtain it. Thus if, in some odd syntax, the symbol 'x' were used to denote metres, then the SimpleUnit instance which resulted would be the same as the OneUnit which resulted from a more conventional syntax.

Also, there is a potential ambiguity if a symbol is recognised in one syntax, but not in another. Thus if the string 'erg' were parsed in a syntax which didn't recognise that, then it would be stored as just that, an unrecognised symbol, not associated with the UnitDefinition for the erg. Similarly, if a unit is parsed with guessing, then we may encounter a unit which is recognised in the sense of OneUnit.isRecognisedUnit(), but not in the sense of OneUnit.isRecognisedUnit(Syntax).

The class's instances are immutable.

  • Method Details

    • getPrefix

      public int getPrefix()
      Returns the prefix of the unit, as a base-ten log. Thus a prefix of "m", for "milli", would produce a prefix of -3.
      Specified by:
      getPrefix in class OneUnit
      Returns:
      the power of ten which multiplies the unit

    • toString

      public String toString()
      Description copied from class: OneUnit
      Format this unit in readable form. The form is unspecified.

      This should not generally be used for formatted output – for that, it will more often be better to use UnitExpr.toString().

      Specified by:
      toString in class OneUnit
      Returns:
      a string representation of the unit

    • toString

      public String toString(Syntax syntax) throws UnwritableExpression
      Description copied from class: OneUnit
      Format this unit in readable form, appropriate to the given syntax. The form is unspecified.

      This should not generally be used for formatted output – for that, it will more often be better to use UnitExpr.toString().

      Specified by:
      toString in class OneUnit
      Parameters:
      syntax - one of the known syntaxes
      Returns:
      a string representation of the unit
      Throws:
      UnwritableExpression - if the unit can't be written in the given syntax

    • unitString

      public String unitString(Syntax syntax) throws UnwritableExpression
      Description copied from class: OneUnit
      Obtains the string representation of the unit, including prefix, in the given syntax. That is, return ‘mm’ not ‘m’ or ‘metre’. If a unit has more than one representation in a given syntax, then this will produced the ‘preferred one’.

      This will fail, with a UnitParserException, in the rare cases where the unit string is inexpressible in the given syntax: for example the CDS syntax permits only the log function to be applied to a unit, and will fail if it is asked to display a different function.

      Specified by:
      unitString in class OneUnit
      Parameters:
      syntax - one of the syntaxes of Syntax
      Returns:
      a non-null string representation of the unit
      Throws:
      UnwritableExpression - if the unit string is inexpressible in the given syntax

    • getBaseUnitDefinition

      public UnitDefinition getBaseUnitDefinition()
      Description copied from class: OneUnit
      Returns the known base unit. If the unit wasn't recognised as a known unit in the syntax in which the string was parsed, then this returns null, though OneUnit.getBaseUnitName() will not.

      Note that the ‘base unit’ is simply the unit without the prefix, and doesn't refer to the fundamental SI base units. Thus in the expression "MW", it is ‘W’, Watt, that is the base unit.

      Specified by:
      getBaseUnitDefinition in class OneUnit
      Returns:
      a base unit

    • getBaseUnitName

      public String getBaseUnitName()
      Description copied from class: OneUnit
      Returns the name of this unit. If the unit is a known one, then this will return a name for the unit such as ‘Metre’, or ‘Julian year’; if it is not, then this can do no more than return the unit symbol.

      This should be used for identification or similar purposes. To write out the unit you should generally use UnitExpr.toString().

      Specified by:
      getBaseUnitName in class OneUnit
      Returns:
      the string name of this unit

    • getBaseUnitString

      public String getBaseUnitString()

    • getDimensions

      public Dimensions getDimensions()
      Description copied from class: OneUnit
      Return the dimensions of the unit, if it is a recognised one. If this isn't a recognised unit, return null.
      Specified by:
      getDimensions in class OneUnit
      Returns:
      the dimensions of the unit, or null if these aren't avaiable

    • getOriginalUnitString

      public String getOriginalUnitString()
      Description copied from class: OneUnit
      Obtains the representation of the unit, as it originally appeared in the parsed input. This will differ from what is produced by unitString if (a) the original was a dispreferred representation of a recognised unit (for example ‘yr’ vs ‘a’), or (b) if the unit was (successfully) guessed from an otherwise unrecognised string.
      Specified by:
      getOriginalUnitString in class OneUnit
      Returns:
      the original input representation of the unit

    • unitString

      public String unitString()
      Obtains the string form of the unit, including prefix, with a default syntax. That is, return 'mm' not 'm'.

      The default syntax is (currently) the syntax with which this unit was originally read.

      Returns:
      a string representation of the unit

    • isRecognisedUnit

      public boolean isRecognisedUnit(Syntax syntax)
      Description copied from class: OneUnit
      Indicates whether the base unit is one of those recognised within the specification of the given syntax. In this context, ‘recognised’ means ‘mentioned in the specification’, so deprecated units count as recognised ones.

      Note that this checks that the unit is a recognised one: we don't (currently) check whether the abbreviation that got us here is a recommended one (for example, ‘pixel’ is a valid FITS/CDS name for pixels, and ‘pix’ is a FITS and OGIP one). This also means that if we guessed a unit, and that unit is a recognised one in this syntax, then this method returns true.

      If the syntax is Syntax.ALL, then this checks whether this is a recognised unit in any syntax.

      Specified by:
      isRecognisedUnit in class OneUnit
      Parameters:
      syntax - one of the syntaxes of Syntax
      Returns:
      true if the unit is recognised
      See Also:

    • isRecognisedUnit

      public boolean isRecognisedUnit()
      Description copied from class: OneUnit
      Indicates whether the base unit is one of those recognised in any syntax.

      This is equivalent to isRecognisedUnit(Syntax.ALL). If this method returns true, then OneUnit.getBaseUnitDefinition() would return non-null, and vice versa if this method returns false.

      Specified by:
      isRecognisedUnit in class OneUnit
      Returns:
      true if the unit is recognised

    • isRecommendedUnit

      public boolean isRecommendedUnit(Syntax syntax)
      Description copied from class: OneUnit
      Indicates whether the base unit is one of those recommended within the specification of the given syntax. In this context, ‘recommended’ means ‘mentioned in the specification’ and not deprecated. Thus all ‘recommended’ units are also a fortiori ‘recognised’.

      Note that this checks that the unit is a recommended one: we don't (currently) check whether the abbreviation that got us here is a recommended one (for example, "pixel" is a valid FITS/CDS name for pixels, and "pix" is a FITS and OGIP one). This also means that if we guessed a unit, and that unit is a recommended one in this syntax, then this method returns true.

      Specified by:
      isRecommendedUnit in class OneUnit
      Parameters:
      syntax - one of the syntaxes of Syntax
      Returns:
      true if the unit is a recommended one
      See Also:

    • satisfiesUsageConstraints

      public boolean satisfiesUsageConstraints(Syntax syntax)
      Description copied from class: OneUnit
      Indicates whether the unit is being used in a way which satisfies any usage constraints. Principally, this tests whether a unit which may not be used with SI prefixes was provided with a prefix, but there may be other constraints present.

      An unrecognised unit has no constraints, and so will always satisfy them; this extends to units which are unrecognised in a particular syntax.

      Specified by:
      satisfiesUsageConstraints in class OneUnit
      Parameters:
      syntax - one of the syntaxes of Syntax
      Returns:
      true if the unit satisfies its usage constraints

    • toDebugString

      public String toDebugString()
      Description copied from class: OneUnit
      Write out the unit in a testable format. This is for debugging and testing.
      Specified by:
      toDebugString in class OneUnit
      Returns:
      a string representation of the unit

    • equals

      public boolean equals(Object o)
      Two units are equal if they have the same power, units and exponent. They don't have to have been obtained from the same syntax, so that in a syntax which (for example) permitted both "yr" and "a" for years, two SimpleUnit instances, obtained from parsing the two alternatives, would be regarded as equal.
      Overrides:
      equals in class Object

    • compareTo

      public int compareTo(OneUnit o)
      Specified by:
      compareTo in interface Comparable<OneUnit>
      Specified by:
      compareTo in class OneUnit

    • hashCode

      public int hashCode()
      Overrides:
      hashCode in class Object