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/*
* Copyright (c) 2015, 2017, 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
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* questions.
*/
package java.util;
import jdk.internal.vm.annotation.Stable;
/**
* An immutable container for a key and a value, suitable for use
* in creating and populating {@code Map} instances.
*
* This is a value-based
* class; use of identity-sensitive operations (including reference equality
* ({@code ==}), identity hash code, or synchronization) on instances of
* {@code KeyValueHolder} may have unpredictable results and should be avoided.
*
* @apiNote
* This class is not public. Instances can be created using the
* {@link Map#entry Map.entry(k, v)} factory method, which is public.
*
*
This class differs from AbstractMap.SimpleImmutableEntry in the following ways:
* it is not serializable, it is final, and its key and value must be non-null.
*
* @param the key type
* @param the value type
*
* @see Map#ofEntries Map.ofEntries()
* @since 9
*/
final class KeyValueHolder implements Map.Entry {
@Stable
final K key;
@Stable
final V value;
KeyValueHolder(K k, V v) {
key = Objects.requireNonNull(k);
value = Objects.requireNonNull(v);
}
/**
* Gets the key from this holder.
*
* @return the key
*/
@Override
public K getKey() {
return key;
}
/**
* Gets the value from this holder.
*
* @return the value
*/
@Override
public V getValue() {
return value;
}
/**
* Throws {@link UnsupportedOperationException}.
*
* @param value ignored
* @return never returns normally
*/
@Override
public V setValue(V value) {
throw new UnsupportedOperationException("not supported");
}
/**
* Compares the specified object with this entry for equality.
* Returns {@code true} if the given object is also a map entry and
* the two entries' keys and values are equal. Note that key and
* value are non-null, so equals() can be called safely on them.
*/
@Override
public boolean equals(Object o) {
if (!(o instanceof Map.Entry))
return false;
Map.Entry e = (Map.Entry)o;
return key.equals(e.getKey()) && value.equals(e.getValue());
}
/**
* Returns the hash code value for this map entry. The hash code
* is {@code key.hashCode() ^ value.hashCode()}. Note that key and
* value are non-null, so hashCode() can be called safely on them.
*/
@Override
public int hashCode() {
return key.hashCode() ^ value.hashCode();
}
/**
* Returns a String representation of this map entry. This
* implementation returns the string representation of this
* entry's key followed by the equals character ("{@code =}")
* followed by the string representation of this entry's value.
*
* @return a String representation of this map entry
*/
@Override
public String toString() {
return key + "=" + value;
}
}