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.

The class's instances are immutable.

Method Summary

int	compareTo(OneUnit o)
boolean	equals(Object o) Two units are equal if they have the same power, units and exponent.
UnitDefinition	getBaseUnitDefinition() Returns the known base unit.
String	getBaseUnitName() Returns the name of this unit.
String	getBaseUnitString() Returns the base unit string, which will only be non-null if this unit was an unrecognised one.
Dimensions	getDimensions() Return the dimensions of the unit, if it is a recognised one.
int	getPrefix() Returns the prefix of the unit, as a base-ten log.
int	hashCode()
boolean	isRecognisedUnit(Syntax syntax) Indicates whether the base unit is one of those recognised within the specification of the given syntax.
boolean	isRecommendedUnit(Syntax syntax) Indicates whether the base unit is one of those recommended within the specification of the given syntax.
boolean	satisfiesUsageConstraints(Syntax syntax) Indicates whether the unit is being used in a way which satisfies any usage constraints.
String	toDebugString() Write out the unit in a testable format.
String	toString() Format this unit in some sort of canonical form.
String	toString(Syntax syntax) Format this unit in some sort of canonical form appropriate to the given syntax.
String	unitString() Obtains the string form of the unit, including prefix, with a default syntax.
String	unitString(Syntax syntax) Obtains the string representation of the unit, including prefix, in the given syntax.

Methods inherited from class uk.me.nxg.unity.OneUnit

getExponent, isQuoted

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Method Detail

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

toString

public String toString()

Description copied from class: OneUnit

Format this unit in some sort of canonical form. The form is unspecified. This should not generally be used for formatted output – for that, it will generally be more appropriate to use UnitExpr.toString().

Specified by:

toString in class OneUnit

toString

public String toString(Syntax syntax)

Description copied from class: OneUnit

Format this unit in some sort of canonical form appropriate to the given syntax. The form is unspecified. This should not generally be used for formatted output – for that, it will generally be more appropriate to use UnitExpr.toString().

Specified by:

toString in class OneUnit

unitString

public String unitString(Syntax syntax)
                  throws UnitParserException

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’.

Specified by:

unitString in class OneUnit

Parameters:

syntax - one of the syntaxes of Syntax

Returns:

a non-null string representation of the unit

Throws:

UnitParserException - if the syntax is unrecognised

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.getBaseUnitString() 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

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.

Specified by:

getBaseUnitName in class OneUnit

getBaseUnitString

public String getBaseUnitString()

Description copied from class: OneUnit

Returns the base unit string, which will only be non-null if this unit was an unrecognised one. This is non-private because UnitExpr needs to know this when it's searching for units in the expression; it's package-only because this is not how clients should format units – they should use the UnitExpr formatting facilities instead.

Specified by:

getBaseUnitString in class OneUnit

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

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.

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 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).

Specified by:

isRecognisedUnit in class OneUnit

Parameters:

syntax - one of the syntaxes of Syntax

See Also:

OneUnit.isRecommendedUnit(uk.me.nxg.unity.Syntax)

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).

Specified by:

isRecommendedUnit in class OneUnit

Parameters:

syntax - one of the syntaxes of Syntax

See Also:

OneUnit.isRecognisedUnit(uk.me.nxg.unity.Syntax)

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

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

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