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/*
* Copyright (c) 2000, 2020, Oracle and/or its affiliates.
*
* Licensed under the Universal Permissive License v 1.0 as shown at
* http://oss.oracle.com/licenses/upl.
*/
package com.tangosol.util.comparator;
import com.tangosol.io.ExternalizableLite;
import com.tangosol.io.pof.PofReader;
import com.tangosol.io.pof.PofWriter;
import com.tangosol.io.pof.PortableObject;
import com.tangosol.util.Base;
import com.tangosol.util.ClassHelper;
import com.tangosol.util.ExternalizableHelper;
import com.tangosol.util.QueryMap;
import com.tangosol.util.extractor.KeyExtractor;
import com.tangosol.util.function.Remote;
import java.io.DataInput;
import java.io.DataOutput;
import java.io.EOFException;
import java.io.IOException;
import java.io.Serializable;
import java.util.Comparator;
import javax.json.bind.annotation.JsonbProperty;
/**
* Null-safe delegating comparator. Null values are evaluated as "less then"
* any non-null value. If the wrapped comparator is not specified then all
* non-null values must implement the {@link java.lang.Comparable} interface.
*
* Use SafeComparator.INSTANCE to obtain an instance of non-delegating
* SafeComparator.
*
* @author gg 2002.12.10
*/
public class SafeComparator
extends Base
implements Remote.Comparator, QueryMapComparator, EntryAwareComparator,
Serializable, ExternalizableLite, PortableObject
{
// ----- constructors ---------------------------------------------------
/**
* Default constructor (for ExternalizableLite and PortableObject).
*/
public SafeComparator()
{
}
/**
* Construct a SafeComparator delegating to the specified (wrapped)
* comparator.
*
* @param comparator Comparator object to delegate comparison of
* non-null values (optional)
*/
public SafeComparator(Comparator comparator)
{
this(comparator, true);
}
/**
* Construct a SafeComparator delegating to the specified (wrapped)
* comparator.
*
* @param comparator Comparator object to delegate comparison of
* non-null values (optional)
* @param fNullFirst flag specifying if null values should be treated as
* "less than" (true) or "greater than" (false) any
* non-null value
*/
public SafeComparator(Comparator comparator, boolean fNullFirst)
{
m_comparator = comparator;
m_fNullFirst = fNullFirst;
}
// ----- Comparator interface -------------------------------------------
/**
* Compares its two arguments for order. Returns a negative integer,
* zero, or a positive integer as the first argument is less than, equal
* to, or greater than the second. Null values are evaluated as "less
* then" any non-null value. If the wrapped comparator is not specified,
* all non-null values must implement the {@link java.lang.Comparable}
* interface.
*
* @param o1 the first object to be compared
* @param o2 the second object to be compared
*
* @return a negative integer, zero, or a positive integer as the first
* argument is less than, equal to, or greater than the second
*
* @throws ClassCastException if the arguments' types prevent them from
* being compared by this Comparator.
*/
public int compare(T o1, T o2)
{
return compareSafe(getComparator(), o1, o2, m_fNullFirst);
}
// ----- QueryMapComparator interface -----------------------------------
/**
* Compare two entries using the underlying comparator. If the wrapped
* comparator does not implement the QueryMapComparator interface, revert
* to the entry values comparison.
*/
public int compareEntries(QueryMap.Entry entry1, QueryMap.Entry entry2)
{
Comparator comparator = getComparator();
return comparator instanceof QueryMapComparator
? ((QueryMapComparator) comparator).compareEntries(entry1, entry2)
: compareSafe(comparator, entry1.getValue(), entry2.getValue());
}
// ----- EntryAwareComparator interface ---------------------------------
/**
* {@inheritDoc}
*/
public boolean isKeyComparator()
{
return isKeyComparator(getComparator());
}
/**
* Check whether the specified comparator expects to compare keys or values.
*
* @param comparator a Comparator to check
*
* @return true if the comparator expects keys; false otherwise
*/
public static boolean isKeyComparator(Comparator comparator)
{
return comparator instanceof KeyExtractor ||
comparator instanceof EntryAwareComparator &&
((EntryAwareComparator) comparator).isKeyComparator();
}
// ----- accessors ------------------------------------------------------
/**
* Obtain the wrapped Comparator.
*
* @return the wrapped Comparator
*/
public Comparator getComparator()
{
return m_comparator;
}
/**
* Obtain the m_fNullFirst flag.
*
* @return the m_fNullFirst flag
*/
public boolean isNullFirst()
{
return m_fNullFirst;
}
// ----- helpers --------------------------------------------------------
/**
* Compares its two arguments for order. Returns a negative integer,
* zero, or a positive integer as the first argument is less than, equal
* to, or greater than the second. Null values are evaluated as
* "less then" any non-null value. Non-null values must implement the
* {@link java.lang.Comparable} interface.
*
* @param comparator a comparator to use for the comparison (optional)
* @param o1 the first object to be compared
* @param o2 the second object to be compared
*
* @return a negative integer, zero, or a positive integer as the first
* argument is less than, equal to, or greater than the second
*
* @throws ClassCastException if the arguments are not Comparable
*/
public static int compareSafe(Comparator comparator, Object o1, Object o2)
{
return compareSafe(comparator, o1, o2, true);
}
/**
* Compares its two arguments for order. Returns a negative integer,
* zero, or a positive integer as the first argument is less than, equal
* to, or greater than the second. Null values are evaluated based on the
* value of a {@code fNullFirst} flag as either "less than" or "greater than"
* any non-null value. Non-null values must implement the
* {@link java.lang.Comparable} interface.
*
* @param comparator a comparator to use for the comparison (optional)
* @param o1 the first object to be compared
* @param o2 the second object to be compared
* @param fNullFirst flag specifying if null values should be treated as
* "less than" (true) or "greater than" (false) any
* non-null value
*
* @return a negative integer, zero, or a positive integer as the first
* argument is less than, equal to, or greater than the second
*
* @throws ClassCastException if the arguments are not Comparable
*/
public static int compareSafe(Comparator comparator, Object o1, Object o2, boolean fNullFirst)
{
if (comparator != null)
{
try
{
return comparator.compare(o1, o2);
}
catch (NullPointerException e) {}
}
if (o1 == null)
{
return o2 == null ? 0 : (fNullFirst ? -1 : +1);
}
if (o2 == null)
{
return (fNullFirst ? +1 : -1);
}
return ((Comparable) o1).compareTo(o2);
}
// ----- Object methods -------------------------------------------------
/**
* Return a human-readable description for this Comparator.
*
* @return a String description of the Comparator
*/
public String toString()
{
return ClassHelper.getSimpleName(getClass()) + " (" + m_comparator + ')';
}
/**
* Determine if two comparators are equal.
*
* @param o the other comparator
*
* @return true if the passed object is equal to this
*/
public boolean equals(Object o)
{
return o instanceof SafeComparator &&
m_fNullFirst == ((SafeComparator) o).m_fNullFirst &&
equals(m_comparator, ((SafeComparator) o).m_comparator);
}
/**
* Return the hash code for this comparator.
*
* @return the hash code value for this comparator
*/
public int hashCode()
{
Comparator comparator = m_comparator;
return (comparator == null ? 17 : comparator.hashCode())
+ (m_fNullFirst ? 1 : 0);
}
// ----- ExternalizableLite interface -----------------------------------
/**
* {@inheritDoc}
*/
public void readExternal(DataInput in)
throws IOException
{
m_comparator = ExternalizableHelper.readObject(in);
try
{
m_fNullFirst = in.readBoolean();
}
catch (EOFException e)
{
// from older release (<= 12.1.3)
}
}
/**
* {@inheritDoc}
*/
public void writeExternal(DataOutput out)
throws IOException
{
ExternalizableHelper.writeObject(out, m_comparator);
out.writeBoolean(m_fNullFirst);
}
// ----- PortableObject interface ---------------------------------------
/**
* {@inheritDoc}
*/
public void readExternal(PofReader in)
throws IOException
{
m_comparator = in.readObject(0);
try
{
m_fNullFirst = in.readBoolean(1);
}
catch (EOFException e)
{
// from older release (<= 12.1.3)
}
}
/**
* {@inheritDoc}
*/
public void writeExternal(PofWriter out)
throws IOException
{
out.writeObject(0, m_comparator);
out.writeBoolean(1, m_fNullFirst);
}
// ----- constants ------------------------------------------------------
/**
* The trivial SafeComparator.
*/
public static final SafeComparator INSTANCE = new SafeComparator();
/**
* Return the trivial SafeComparator.
*/
public static SafeComparator INSTANCE()
{
return INSTANCE;
}
// ----- data members ---------------------------------------------------
/**
* The wrapped Comparator. Could be null.
*/
@JsonbProperty("comparator")
protected Comparator m_comparator;
/**
* Flag specifying if nulls should be sorted as less (first) or greater
* (last) than all non-null elements. Default is "less than" (first).
*/
@JsonbProperty("nullFirst")
protected boolean m_fNullFirst = true;
}