# Interface Datatype

public interface Datatype
Datatype object. This object has the following functionality:

1. functionality to identify a class of character sequences. This is done through the isValid method.
2. functionality to produce a "value object" from a character sequence and context information.
3. functionality to test the equality of two value objects.

This interface also defines the createStreamingValidator method, which is intended to efficiently support the validation of large character sequences.

Author:
  James Clark, Kohsuke KAWAGUCHI

- ## Field Summary

  Fields
  Modifier and Type
  Field
  Description
  `static final int`
  `ID_TYPE_ID`
  Indicates that RELAX NG compatibility processors should treat this datatype as having ID semantics.
  `static final int`
  `ID_TYPE_IDREF`
  Indicates that RELAX NG compatibility processors should treat this datatype as having IDREF semantics.
  `static final int`
  `ID_TYPE_IDREFS`
  Indicates that RELAX NG compatibility processors should treat this datatype as having IDREFS semantics.
  `static final int`
  `ID_TYPE_NULL`
  Indicates that the datatype doesn't have ID/IDREF semantics.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `void`
  `checkValid(String literal, ValidationContext context)`
  Similar to the isValid method but throws an exception with diagnosis in case of errors.
  `DatatypeStreamingValidator`
  `createStreamingValidator(ValidationContext context)`
  Creates an instance of a streaming validator for this type.
  `Object`
  `createValue(String literal, ValidationContext context)`
  Converts lexcial value and the current context to the corresponding value object.
  `int`
  `getIdType()`
  Checks if the ID/IDREF semantics is associated with this datatype.
  `boolean`
  `isContextDependent()`
  Checks if this datatype may need a context object for the validation.
  `boolean`
  `isValid(String literal, ValidationContext context)`
  Checks if the specified 'literal' matches this Datatype with respect to the current context.
  `boolean`
  `sameValue(Object value1, Object value2)`
  Tests the equality of two value objects which were originally created by the createValue method of this object.
  `int`
  `valueHashCode(Object value)`
  Computes the hash code for a value object, which is consistent with the sameValue method.

- ## Field Details

  - ### ID_TYPE_NULL

    static final int ID_TYPE_NULL
    Indicates that the datatype doesn't have ID/IDREF semantics. This value is one of the possible return values of the `getIdType()` method.
    See Also:
      - Constant Field Values

  - ### ID_TYPE_ID

    static final int ID_TYPE_ID
    Indicates that RELAX NG compatibility processors should treat this datatype as having ID semantics. This value is one of the possible return values of the `getIdType()` method.
    See Also:
      - Constant Field Values

  - ### ID_TYPE_IDREF

    static final int ID_TYPE_IDREF
    Indicates that RELAX NG compatibility processors should treat this datatype as having IDREF semantics. This value is one of the possible return values of the `getIdType()` method.
    See Also:
      - Constant Field Values

  - ### ID_TYPE_IDREFS

    static final int ID_TYPE_IDREFS
    Indicates that RELAX NG compatibility processors should treat this datatype as having IDREFS semantics. This value is one of the possible return values of the `getIdType()` method.
    See Also:
      - Constant Field Values

- ## Method Details

  - ### isValid

    boolean isValid(String literal, ValidationContext context)
    Checks if the specified 'literal' matches this Datatype with respect to the current context.
    Parameters:
      `literal` - the lexical representation to be checked.
      `context` - If this datatype is context-dependent (i.e. the `isContextDependent()` method returns true), then the caller must provide a non-null valid context object. Otherwise, the caller can pass null.
    Returns:
      true if the 'literal' is a member of this Datatype; false if it's not a member of this Datatype.

  - ### checkValid

    void checkValid(String literal, ValidationContext context) throws DatatypeException
    Similar to the isValid method but throws an exception with diagnosis in case of errors.

    If the specified 'literal' is a valid lexical representation for this datatype, then this method must return without throwing any exception. If not, the callee must throw an exception (with diagnosis message, if possible.)

    The application can use this method to provide detailed error message to users. This method is kept separate from the isValid method to achieve higher performance during normal validation.

    Throws:
      `DatatypeException` - If the given literal is invalid, then this exception is thrown. If the callee supports error diagnosis, then the exception should contain a diagnosis message.

  - ### createStreamingValidator

    DatatypeStreamingValidator createStreamingValidator(ValidationContext context)
    Creates an instance of a streaming validator for this type.

    By using streaming validators instead of the isValid method, the caller can avoid keeping the entire string, which is sometimes quite big, in memory.

    Parameters:
      `context` - If this datatype is context-dependent (i.e. the `isContextDependent()` method returns true), then the caller must provide a non-null valid context object. Otherwise, the caller can pass null. The callee may keep a reference to this context object only while the returned streaming validator is being used.

  - ### createValue

    Object createValue(String literal, ValidationContext context)
    Converts lexcial value and the current context to the corresponding value object.

    The caller cannot generally assume that the value object is a meaningful Java object. For example, the caller cannot expect this method to return `java.lang.Number` type for the "integer" type of XML Schema Part 2.

    Also, the caller cannot assume that the equals method and the hashCode method of the value object are consistent with the semantics of the datatype. For that purpose, the sameValue method and the valueHashCode method have to be used. Note that this means you cannot use classes like `java.util.Hashtable` to store the value objects.

    The returned value object should be used solely for the sameValue and valueHashCode methods.

    Parameters:
      `context` - If this datatype is context-dependent (when the `isContextDependent()` method returns true), then the caller must provide a non-null valid context object. Otherwise, the caller can pass null.
    Returns:
      null when the given lexical value is not a valid lexical value for this type.

  - ### sameValue

    boolean sameValue(Object value1, Object value2)
    Tests the equality of two value objects which were originally created by the createValue method of this object. The behavior is undefined if objects not created by this type are passed. It is the caller's responsibility to ensure that value objects belong to this type.
    Returns:
      true if two value objects are considered equal according to the definition of this datatype; false if otherwise.

  - ### valueHashCode

    int valueHashCode(Object value)
    Computes the hash code for a value object, which is consistent with the sameValue method.
    Returns:
      hash code for the specified value object.

  - ### getIdType

    int getIdType()
    Checks if the ID/IDREF semantics is associated with this datatype.

    This method is introduced to support the RELAX NG DTD compatibility spec. (Of course it's always free to use this method for other purposes.)

    If you are implementing a datatype library and have no idea about the "RELAX NG DTD compatibility" thing, just return `ID_TYPE_NULL` is fine.

    Returns:
      If this datatype doesn't have any ID/IDREF semantics, it returns `ID_TYPE_NULL`. If it has such a semantics (for example, XSD:ID, XSD:IDREF and comp:ID type), then it returns `ID_TYPE_ID`, `ID_TYPE_IDREF` or `ID_TYPE_IDREFS`.

  - ### isContextDependent

    boolean isContextDependent()
    Checks if this datatype may need a context object for the validation.

    The callee must return true even when the context is not always necessary. (For example, the "QName" type doesn't need a context object when validating unprefixed string. But nonetheless QName must return true.)

    XSD's `string` and `short` types are examples of context-independent datatypes. Its `QName` and `ENTITY` types are examples of context-dependent datatypes.

    When a datatype is context-independent, then the `isValid(java.lang.String, org.relaxng.datatype.ValidationContext)` method, the `checkValid(java.lang.String, org.relaxng.datatype.ValidationContext)` method, the `createStreamingValidator(org.relaxng.datatype.ValidationContext)` method and the `createValue(java.lang.String, org.relaxng.datatype.ValidationContext)` method can be called without providing a context object.

    Returns:
      true if this datatype is context-dependent (it needs a context object sometimes); false if this datatype is context-independent (it never needs a context object).