--- /dev/null
+/*
+ * @(#)Comparator.java 1.22 03/12/19
+ *
+ * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
+ * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
+ */
+
+package instrumented.java15.util;
+
+/**
+ * A comparison function, which imposes a <i>total ordering</i> on some
+ * collection of objects. Comparators can be passed to a sort method (such as
+ * <tt>Collections.sort</tt>) to allow precise control over the sort order.
+ * Comparators can also be used to control the order of certain data
+ * structures (such as <tt>TreeSet</tt> or <tt>TreeMap</tt>).<p>
+ *
+ * The ordering imposed by a Comparator <tt>c</tt> on a set of elements
+ * <tt>S</tt> is said to be <i>consistent with equals</i> if and only if
+ * <tt>(compare((Object)e1, (Object)e2)==0)</tt> has the same boolean value as
+ * <tt>e1.equals((Object)e2)</tt> for every <tt>e1</tt> and <tt>e2</tt> in
+ * <tt>S</tt>.<p>
+ *
+ * Caution should be exercised when using a comparator capable of imposing an
+ * ordering inconsistent with equals to order a sorted set (or sorted map).
+ * Suppose a sorted set (or sorted map) with an explicit Comparator <tt>c</tt>
+ * is used with elements (or keys) drawn from a set <tt>S</tt>. If the
+ * ordering imposed by <tt>c</tt> on <tt>S</tt> is inconsistent with equals,
+ * the sorted set (or sorted map) will behave "strangely." In particular the
+ * sorted set (or sorted map) will violate the general contract for set (or
+ * map), which is defined in terms of <tt>equals</tt>.<p>
+ *
+ * For example, if one adds two keys <tt>a</tt> and <tt>b</tt> such that
+ * <tt>(a.equals((Object)b) && c.compare((Object)a, (Object)b) != 0)</tt> to a
+ * sorted set with comparator <tt>c</tt>, the second <tt>add</tt> operation
+ * will return false (and the size of the sorted set will not increase)
+ * because <tt>a</tt> and <tt>b</tt> are equivalent from the sorted set's
+ * perspective.<p>
+ *
+ * Note: It is generally a good idea for comparators to implement
+ * <tt>java.io.Serializable</tt>, as they may be used as ordering methods in
+ * serializable data structures (like <tt>TreeSet</tt>, <tt>TreeMap</tt>). In
+ * order for the data structure to serialize successfully, the comparator (if
+ * provided) must implement <tt>Serializable</tt>.<p>
+ *
+ * For the mathematically inclined, the <i>relation</i> that defines
+ * the <i>total order</i> that a given comparator <tt>c</tt> imposes on a
+ * given set of objects <tt>S</tt> is:<pre>
+ * {(x, y) such that c.compare((Object)x, (Object)y) <= 0}.
+ * </pre> The <i>quotient</i> for this total order is:<pre>
+ * {(x, y) such that c.compare((Object)x, (Object)y) == 0}.
+ * </pre>
+ *
+ * It follows immediately from the contract for <tt>compare</tt> that the
+ * quotient is an <i>equivalence relation</i> on <tt>S</tt>, and that the
+ * natural ordering is a <i>total order</i> on <tt>S</tt>. When we say that
+ * the ordering imposed by <tt>c</tt> on <tt>S</tt> is <i>consistent with
+ * equals</i>, we mean that the quotient for the natural ordering is the
+ * equivalence relation defined by the objects' <tt>equals(Object)</tt>
+ * method(s):<pre>
+ * {(x, y) such that x.equals((Object)y)}.
+ * </pre><p>
+ *
+ * This interface is a member of the
+ * <a href="{@docRoot}/../guide/collections/index.html">
+ * Java Collections Framework</a>.
+ *
+ * @author Josh Bloch
+ * @author Neal Gafter
+ * @version 1.22, 12/19/03
+ * @see Comparable
+ * @see Arrays#sort(Object[], Comparator)
+ * @see TreeMap
+ * @see TreeSet
+ * @see SortedMap
+ * @see SortedSet
+ * @see java.io.Serializable
+ * @since 1.2
+ */
+
+public interface Comparator<T> {
+ /**
+ * 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.<p>
+ *
+ * The implementor must ensure that <tt>sgn(compare(x, y)) ==
+ * -sgn(compare(y, x))</tt> for all <tt>x</tt> and <tt>y</tt>. (This
+ * implies that <tt>compare(x, y)</tt> must throw an exception if and only
+ * if <tt>compare(y, x)</tt> throws an exception.)<p>
+ *
+ * The implementor must also ensure that the relation is transitive:
+ * <tt>((compare(x, y)>0) && (compare(y, z)>0))</tt> implies
+ * <tt>compare(x, z)>0</tt>.<p>
+ *
+ * Finally, the implementer must ensure that <tt>compare(x, y)==0</tt>
+ * implies that <tt>sgn(compare(x, z))==sgn(compare(y, z))</tt> for all
+ * <tt>z</tt>.<p>
+ *
+ * It is generally the case, but <i>not</i> strictly required that
+ * <tt>(compare(x, y)==0) == (x.equals(y))</tt>. Generally speaking,
+ * any comparator that violates this condition should clearly indicate
+ * this fact. The recommended language is "Note: this comparator
+ * imposes orderings that are inconsistent with equals."
+ *
+ * @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.
+ */
+ int compare(T o1, T o2);
+
+ /**
+ *
+ * Indicates whether some other object is "equal to" this
+ * Comparator. This method must obey the general contract of
+ * <tt>Object.equals(Object)</tt>. Additionally, this method can return
+ * <tt>true</tt> <i>only</i> if the specified Object is also a comparator
+ * and it imposes the same ordering as this comparator. Thus,
+ * <code>comp1.equals(comp2)</code> implies that <tt>sgn(comp1.compare(o1,
+ * o2))==sgn(comp2.compare(o1, o2))</tt> for every object reference
+ * <tt>o1</tt> and <tt>o2</tt>.<p>
+ *
+ * Note that it is <i>always</i> safe <i>not</i> to override
+ * <tt>Object.equals(Object)</tt>. However, overriding this method may,
+ * in some cases, improve performance by allowing programs to determine
+ * that two distinct Comparators impose the same order.
+ *
+ * @param obj the reference object with which to compare.
+ * @return <code>true</code> only if the specified object is also
+ * a comparator and it imposes the same ordering as this
+ * comparator.
+ * @see java.lang.Object#equals(java.lang.Object)
+ * @see java.lang.Object#hashCode()
+ */
+ boolean equals(Object obj);
+}
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