Package org.apache.sis.util
Interface ObjectConverter<S,T>
- Type Parameters:
S- the type of objects to convert.T- the type of converted objects.
- All Superinterfaces:
Function<S,T>
A function which converts instances of source type to instances of target type.
The source and target types may be the same, in which case the
ObjectConverter actually converts
the values rather than the type.
The main method of this interface is apply(Object), which receives an object of type
S and returns an object of type T. The set of all S values for which
apply(S) does not throw UnconvertibleObjectException is called the domain
of this function, regardless of whether the T result is null or not.
Function properties
Some characteristics about the S to T mapping are given by theproperties() enumeration, together with the getSourceClass() and
getTargetClass() methods. Some possible function properties are:
- Injective if no pair of S can produce
the same T value (e.g.: conversions from
IntegertoString). - Surjective if every values of T can be
created from one or many values of S (e.g.: conversions from
StringtoInteger). - Bijective if there is a one-to-one relationship between the S and T values.
- Order preserving if any sequence of
increasing S values (in the sense of
Comparable) is mapped to a sequence of increasing T values. - Order reversing if any sequence of
increasing S values (in the sense of
Comparable) is mapped to a sequence of decreasing T values.
Example:
The function properties regarding order is important when converting
Below are some guidelines about the function properties that a converter can declare:
Range objects.
For example if the converter reverses the value ordering (e.g. reverses the sign of numerical values), then the
minimum and maximum values in each Range instance need to be interchanged. If the ordering is not preserved
at all (neither directly or reversed), as for example in the conversion from Number to String, then
we cannot convert ranges at all.- If
apply(S)returnsnullfor unconvertible objects, then thisObjectConvertercannot be declared injective because more than one S value can produce the same T value (namelynull). - If
apply(S)throws an exception for unconvertible objects, then thisObjectConvertercan be declared as an injective function if the other values met the criteria.
- Since:
- 0.3
- See Also:
Defined in the sis-utility module
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Method Summary
Modifier and TypeMethodDescriptionConverts the given object from the source type S to the target type T.Returns the type of objects to convert.Returns the type of converted objects.inverse()Returns a converter capable to convert instances of T back to instances of S.Returns the manner in which source values (S) are mapped to target values (T).
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Method Details
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properties
Set<FunctionProperty> properties()Returns the manner in which source values (S) are mapped to target values (T). Some possible function properties are:- Injective if no pair of S can produce
the same T value (e.g.: conversions from
IntegertoString). - Surjective if every values of T can be
created from one or many values of S (e.g.: conversions from
StringtoInteger). - Bijective if there is a one-to-one relationship between the S and T values.
- Order preserving if any sequence of
increasing S values (in the sense of
Comparable) is mapped to a sequence of increasing T values. - Order reversing if any sequence of
increasing S values (in the sense of
Comparable) is mapped to a sequence of decreasing T values.
apply(Object)method returnsnullfor unconvertible source values, then this properties set cannot containFunctionProperty.INJECTIVEbecause more than one source value could be converted to the samenulltarget value.- Returns:
- the manners in which source values are mapped to target values. May be an empty set, but never null.
- Injective if no pair of S can produce
the same T value (e.g.: conversions from
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getSourceClass
Returns the type of objects to convert.- Returns:
- the type of objects to convert.
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getTargetClass
Returns the type of converted objects.- Returns:
- the type of converted objects.
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apply
Converts the given object from the source type S to the target type T. If the given object cannot be converted, then this method may either returnsnullor throws an exception, at implementation choice (except for injective functions, which must throw an exception - see the class Javadoc for more discussion about function properties).Example: in Apache SIS implementation, converters fromStringtoNumberdistinguish two kinds of unconvertible objects:- Null or empty source string result in a
nullvalue to be returned. - All other kind of unparsable strings results in an exception to be thrown.
""value is unconvertible but nevertheless considered as part of the converter domain, and is mapped to "no number". All other unparsable strings are considered outside the converter domain.- Specified by:
applyin interfaceFunction<S,T> - Parameters:
object- the object to convert, ornull.- Returns:
- the converted object, or
null. - Throws:
UnconvertibleObjectException- if the given object is not an element of the function domain.
- Null or empty source string result in a
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inverse
Returns a converter capable to convert instances of T back to instances of S. Before to invoke this method, callers can verify if this converter is invertible as below:if (converter.properties().contains(FunctionProperty.INVERTIBLE)) { // Call to converter.inverse() is allowed here. }- Returns:
- a converter for converting instances of T back to instances of S.
- Throws:
UnsupportedOperationException- if this converter is not invertible.- See Also:
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