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 *
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 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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package org.hsqldb.lib;

/**
 * Interface for equality comparison.<p>
 *
 * The equals and hashCode methods of this interace are used instead of
 * the methods of the compared Objects.<p>
 *
 * The DefaultComparator implmentation calls the Object's methods.<p>
 *
 * The IdentityComparator implementation uses {@code ==} instead of the equals
 * method of the Object.<p>
 *
 * Updated for generics fredt@users.
 *
 * @author fredt@users
 * @version 2.7.3
 * @since 2.0
 */
public interface ObjectComparator<T> {

    boolean equals(T a, T b);

    int hashCode(T a);

    long longKey(T a);

    ObjectComparator defaultComparator  = new DefaultComparator();
    ObjectComparator identityComparator = new IdentityComparator();

    /**
     * Comparator that uses identity for Object equality.
     */
    class IdentityComparator<T> implements ObjectComparator<T> {

        public boolean equals(T a, T b) {
            return a == b;
        }

        public int hashCode(T a) {
            return a == null
                   ? 0
                   : a.hashCode();
        }

        public long longKey(T a) {
            return 0L;
        }
    }

    /**
     * Comparator that uses the equals and hash code methods of Objects.
     */
    class DefaultComparator<T> implements ObjectComparator<T> {

        public boolean equals(T a, T b) {
            return a == b || (a != null && a.equals(b));
        }

        public int hashCode(T a) {
            return a == null
                   ? 0
                   : a.hashCode();
        }

        public long longKey(T a) {
            return 0L;
        }
    }
}
