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	/*
	* Copyright (c) 2016, 2021, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/
	package java.lang;

	import jdk.internal.reflect.ReflectionFactory;

	import java.lang.reflect.Method;
	import java.lang.reflect.Modifier;
	import java.security.AccessController;
	import java.util.Arrays;
	import java.util.LinkedHashMap;
	import java.util.Map;

	/**
	* A collection of most specific public methods. Methods are added to it using
	* {@link #merge(Method)} method. Only the most specific methods for a
	* particular signature are kept.
	*/
	final class PublicMethods {

	/**
	* a map of (method name, parameter types) -> linked list of Method(s)
	*/
	private final Map<Key, MethodList> map = new LinkedHashMap<>();

	/**
	* keeps track of the number of collected methods
	*/
	private int methodCount;

	/**
	* Merges new method with existing methods. New method is either
	* ignored (if a more specific method with same signature exists) or added
	* to the collection. When it is added to the collection, it may replace one
	* or more existing methods with same signature if they are less specific
	* than added method.
	* See comments in code...
	*/
	void merge(Method method) {
	Key key = new Key(method);
	MethodList existing = map.get(key);
	int xLen = existing == null ? 0 : existing.length();
	MethodList merged = MethodList.merge(existing, method);
	methodCount += merged.length() - xLen;
	// replace if head of list changed
	if (merged != existing) {
	map.put(key, merged);
	}
	}

	/**
	* Dumps methods to array.
	*/
	Method[] toArray() {
	Method[] array = new Method[methodCount];
	int i = 0;
	for (MethodList ml : map.values()) {
	for (; ml != null; ml = ml.next) {
	array[i++] = ml.method;
	}
	}
	return array;
	}

	/**
	* Method (name, parameter types) tuple.
	*/
	private static final class Key {
	@SuppressWarnings("removal")
	private static final ReflectionFactory reflectionFactory =
	AccessController.doPrivileged(
	new ReflectionFactory.GetReflectionFactoryAction());

	private final String name; // must be interned (as from Method.getName())
	private final Class<?>[] ptypes;

	Key(Method method) {
	name = method.getName();
	ptypes = reflectionFactory.getExecutableSharedParameterTypes(method);
	}

	static boolean matches(Method method,
	String name, // may not be interned
	Class<?>[] ptypes) {
	return method.getName().equals(name) &&
	Arrays.equals(
	reflectionFactory.getExecutableSharedParameterTypes(method),
	ptypes
	);
	}

	@Override
	public boolean equals(Object o) {
	if (this == o) return true;
	//noinspection StringEquality (guaranteed interned String(s))
	return (o instanceof Key that)
	&& name == that.name
	&& Arrays.equals(ptypes, that.ptypes);
	}

	@Override
	public int hashCode() {
	return System.identityHashCode(name) + // guaranteed interned String
	31 * Arrays.hashCode(ptypes);
	}
	}

	/**
	* Node of a inked list containing Method(s) sharing the same
	* (name, parameter types) tuple.
	*/
	static final class MethodList {
	Method method;
	MethodList next;

	private MethodList(Method method) {
	this.method = method;
	}

	/**
	* @return the head of a linked list containing given {@code methods}
	* filtered by given method {@code name}, parameter types
	* {@code ptypes} and including or excluding static methods as
	* requested by {@code includeStatic} flag.
	*/
	static MethodList filter(Method[] methods, String name,
	Class<?>[] ptypes, boolean includeStatic) {
	MethodList head = null, tail = null;
	for (Method method : methods) {
	if ((includeStatic \|\| !Modifier.isStatic(method.getModifiers())) &&
	Key.matches(method, name, ptypes)) {
	if (tail == null) {
	head = tail = new MethodList(method);
	} else {
	tail = tail.next = new MethodList(method);
	}
	}
	}
	return head;
	}

	/**
	* This method should only be called with the {@code head} (possibly null)
	* of a list of Method(s) that share the same (method name, parameter types)
	* and another {@code methodList} that also contains Method(s) with the
	* same and equal (method name, parameter types) as the 1st list.
	* It modifies the 1st list and returns the head of merged list
	* containing only the most specific methods for each signature
	* (i.e. return type). The returned head of the merged list may or
	* may not be the same as the {@code head} of the given list.
	* The given {@code methodList} is not modified.
	*/
	static MethodList merge(MethodList head, MethodList methodList) {
	for (MethodList ml = methodList; ml != null; ml = ml.next) {
	head = merge(head, ml.method);
	}
	return head;
	}

	private static MethodList merge(MethodList head, Method method) {
	Class<?> dclass = method.getDeclaringClass();
	Class<?> rtype = method.getReturnType();
	MethodList prev = null;
	for (MethodList l = head; l != null; l = l.next) {
	// eXisting method
	Method xmethod = l.method;
	// only merge methods with same signature:
	// (return type, name, parameter types) tuple
	// as we only keep methods with same (name, parameter types)
	// tuple together in one list, we only need to check return type
	if (rtype == xmethod.getReturnType()) {
	Class<?> xdclass = xmethod.getDeclaringClass();
	if (dclass.isInterface() == xdclass.isInterface()) {
	// both methods are declared by interfaces
	// or both by classes
	if (dclass.isAssignableFrom(xdclass)) {
	// existing method is the same or overrides
	// new method - ignore new method
	return head;
	}
	if (xdclass.isAssignableFrom(dclass)) {
	// new method overrides existing
	// method - knock out existing method
	if (prev != null) {
	prev.next = l.next;
	} else {
	head = l.next;
	}
	// keep iterating
	} else {
	// unrelated (should only happen for interfaces)
	prev = l;
	// keep iterating
	}
	} else if (dclass.isInterface()) {
	// new method is declared by interface while
	// existing method is declared by class -
	// ignore new method
	return head;
	} else /* xdclass.isInterface() */ {
	// new method is declared by class while
	// existing method is declared by interface -
	// knock out existing method
	if (prev != null) {
	prev.next = l.next;
	} else {
	head = l.next;
	}
	// keep iterating
	}
	} else {
	// distinct signatures
	prev = l;
	// keep iterating
	}
	}
	// append new method to the list
	if (prev == null) {
	head = new MethodList(method);
	} else {
	prev.next = new MethodList(method);
	}
	return head;
	}

	private int length() {
	int len = 1;
	for (MethodList ml = next; ml != null; ml = ml.next) {
	len++;
	}
	return len;
	}

	/**
	* @return 1st method in list with most specific return type
	*/
	Method getMostSpecific() {
	Method m = method;
	Class<?> rt = m.getReturnType();
	for (MethodList ml = next; ml != null; ml = ml.next) {
	Method m2 = ml.method;
	Class<?> rt2 = m2.getReturnType();
	if (rt2 != rt && rt.isAssignableFrom(rt2)) {
	// found more specific return type
	m = m2;
	rt = rt2;
	}
	}
	return m;
	}
	}
	}

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