Package org.apache.flink.api.java.typeutils.runtime

Class GenericTypeComparator<T extends Comparable<T>>

    • Constructor Detail

      • GenericTypeComparator

        public GenericTypeComparator​(boolean ascending,
                             TypeSerializer<T> serializer,
                             Class<T> type)

    • Method Detail

      • hash

        public int hash​(T record)
        Description copied from class: TypeComparator
        Computes a hash value for the given record. The hash value should include all fields in the record relevant to the comparison.

        The hash code is typically not used as it is in hash tables and for partitioning, but it is further scrambled to make sure that a projection of the hash values to a lower cardinality space is as results in a rather uniform value distribution. However, any collisions produced by this method cannot be undone. While it is NOT important to create hash codes that cover the full spectrum of bits in the integer, it IS important to avoid collisions when combining two value as much as possible.

        Specified by:
        hash in class TypeComparator<T extends Comparable<T>>
        Parameters:
        record - The record to be hashed.
        Returns:
        A hash value for the record.
        See Also:
        Object.hashCode()

      • setReference

        public void setReference​(T toCompare)
        Description copied from class: TypeComparator
        Sets the given element as the comparison reference for future calls to TypeComparator.equalToReference(Object) and TypeComparator.compareToReference(TypeComparator). This method must set the given element into this comparator instance's state. If the comparison happens on a subset of the fields from the record, this method may extract those fields.

        A typical example for checking the equality of two elements is the following: 

        
 E e1 = ...;
 E e2 = ...;

 TypeComparator<E> acc = ...;

 acc.setReference(e1);
 boolean equal = acc.equalToReference(e2);
        The rational behind this method is that elements are typically compared using certain features that are extracted from them, (such de-serializing as a subset of fields). When setting the reference, this extraction happens. The extraction needs happen only once per element, even though an element is often compared to multiple other elements, such as when finding equal elements in the process of grouping the elements.
        Specified by:
        setReference in class TypeComparator<T extends Comparable<T>>
        Parameters:
        toCompare - The element to set as the comparison reference.

      • equalToReference

        public boolean equalToReference​(T candidate)
        Description copied from class: TypeComparator
        Checks, whether the given element is equal to the element that has been set as the comparison reference in this comparator instance.
        Specified by:
        equalToReference in class TypeComparator<T extends Comparable<T>>
        Parameters:
        candidate - The candidate to check.
        Returns:
        True, if the element is equal to the comparison reference, false otherwise.
        See Also:
        TypeComparator.setReference(Object)

      • compareToReference

        public int compareToReference​(TypeComparator<T> referencedComparator)
        Description copied from class: TypeComparator
        This method compares the element that has been set as reference in this type accessor, to the element set as reference in the given type accessor. Similar to comparing two elements e1 and e2 via a comparator, this method can be used the following way. 
        
 E e1 = ...;
 E e2 = ...;

 TypeComparator<E> acc1 = ...;
 TypeComparator<E> acc2 = ...;

 acc1.setReference(e1);
 acc2.setReference(e2);

 int comp = acc1.compareToReference(acc2);
        The rational behind this method is that elements are typically compared using certain features that are extracted from them, (such de-serializing as a subset of fields). When setting the reference, this extraction happens. The extraction needs happen only once per element, even though an element is typically compared to many other elements when establishing a sorted order. The actual comparison performed by this method may be very cheap, as it happens on the extracted features.
        Specified by:
        compareToReference in class TypeComparator<T extends Comparable<T>>
        Parameters:
        referencedComparator - The type accessors where the element for comparison has been set as reference.
        Returns:
        A value smaller than zero, if the reference value of referencedAccessors is smaller than the reference value of this type accessor; a value greater than zero, if it is larger; zero, if both are equal.
        See Also:
        TypeComparator.setReference(Object)

      • supportsNormalizedKey

        public boolean supportsNormalizedKey()
        Description copied from class: TypeComparator
        Checks whether the data type supports the creation of a normalized key for comparison.
        Specified by:
        supportsNormalizedKey in class TypeComparator<T extends Comparable<T>>
        Returns:
        True, if the data type supports the creation of a normalized key for comparison, false otherwise.

      • getNormalizeKeyLen

        public int getNormalizeKeyLen()
        Description copied from class: TypeComparator
        Gets the number of bytes that the normalized key would maximally take. A value of Integer.MAX_VALUE is interpreted as infinite.
        Specified by:
        getNormalizeKeyLen in class TypeComparator<T extends Comparable<T>>
        Returns:
        The number of bytes that the normalized key would maximally take.

      • isNormalizedKeyPrefixOnly

        public boolean isNormalizedKeyPrefixOnly​(int keyBytes)
        Description copied from class: TypeComparator
        Checks, whether the given number of bytes for a normalized is only a prefix to determine the order of elements of the data type for which this comparator provides the comparison methods. For example, if the data type is ordered with respect to an integer value it contains, then this method would return true, if the number of key bytes is smaller than four.
        Specified by:
        isNormalizedKeyPrefixOnly in class TypeComparator<T extends Comparable<T>>
        Returns:
        True, if the given number of bytes is only a prefix, false otherwise.

      • putNormalizedKey

        public void putNormalizedKey​(T record,
                             MemorySegment target,
                             int offset,
                             int numBytes)
        Description copied from class: TypeComparator
        Writes a normalized key for the given record into the target byte array, starting at the specified position and writing exactly the given number of bytes. Note that the comparison of the bytes is treating the bytes as unsigned bytes: int byteI = bytes[i] & 0xFF;

        If the meaningful part of the normalized key takes less than the given number of bytes, then it must be padded. Padding is typically required for variable length data types, such as strings. The padding uses a special character, either 0 or 0xff, depending on whether shorter values are sorted to the beginning or the end.

        This method is similar to NormalizableKey.copyNormalizedKey(MemorySegment, int, int). In the case that multiple fields of a record contribute to the normalized key, it is crucial that the fields align on the byte field, i.e. that every field always takes up the exact same number of bytes.

        Specified by:
        putNormalizedKey in class TypeComparator<T extends Comparable<T>>
        Parameters:
        record - The record for which to create the normalized key.
        target - The byte array into which to write the normalized key bytes.
        offset - The offset in the byte array, where to start writing the normalized key bytes.
        numBytes - The number of bytes to be written exactly.
        See Also:
        NormalizableKey.copyNormalizedKey(MemorySegment, int, int)

      • invertNormalizedKey

        public boolean invertNormalizedKey()
        Description copied from class: TypeComparator
        Flag whether normalized key comparisons should be inverted key should be interpreted inverted, i.e. descending.
        Specified by:
        invertNormalizedKey in class TypeComparator<T extends Comparable<T>>
        Returns:
        True, if all normalized key comparisons should invert the sign of the comparison result, false if the normalized key should be used as is.

      • duplicate

        public TypeComparator<T> duplicate()
        Description copied from class: TypeComparator
        Creates a copy of this class. The copy must be deep such that no state set in the copy affects this instance of the comparator class.
        Specified by:
        duplicate in class TypeComparator<T extends Comparable<T>>
        Returns:
        A deep copy of this comparator instance.

      • extractKeys

        public int extractKeys​(Object record,
                       Object[] target,
                       int index)
        Description copied from class: TypeComparator
        Extracts the key fields from a record. This is for use by the PairComparator to provide interoperability between different record types. Note, that at least one key should be extracted.
        Specified by:
        extractKeys in class TypeComparator<T extends Comparable<T>>
        Parameters:
        record - The record that contains the key(s)
        target - The array to write the key(s) into.
        index - The offset of the target array to start writing into.
        Returns:
        the number of keys added to target.

      • supportsSerializationWithKeyNormalization

        public boolean supportsSerializationWithKeyNormalization()
        Description copied from class: TypeComparator
        Check whether this comparator supports to serialize the record in a format that replaces its keys by a normalized key.
        Specified by:
        supportsSerializationWithKeyNormalization in class TypeComparator<T extends Comparable<T>>
        Returns:
        True, if the comparator supports that specific form of serialization, false if not.