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senderic/IdentityLinkedHashMap.java

Created September 27, 2021 16:55
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  1. senderic created this gist Sep 27, 2021.
    92 changes: 92 additions & 0 deletions IdentityLinkedHashMap.java
    View file
    Original file line number Diff line number Diff line change
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    package com.ericsender;

    import com.google.common.base.Equivalence;
    import com.google.common.collect.Iterators;

    import java.util.*;

    /**
    * Combined LinkedHashMap with IdentityHashMap.
    * Uses the Google common's Equivalence method of implementing IdentityHashMaps.
    * <p>
    * Based on https://stackoverflow.com/a/46561815/1582712 (author: https://stackoverflow.com/users/1450343/moddyfire)
    */
    public class IdentityLinkedHashMap<K, T> extends AbstractMap<K, T> {

    private final IdentityLinkedHashSet set = new IdentityLinkedHashSet();

    @Override
    public Set<Entry<K, T>> entrySet() {
    return set;
    }

    @Override
    public T put(K k, T t) {
    return set.innerMap.put(Equivalence.identity().wrap(k), t);
    }

    @Override
    public boolean containsKey(Object arg0) {
    return set.contains(arg0);
    }

    @Override
    public T remove(Object arg0) {
    return set.innerMap.remove(Equivalence.identity().wrap(arg0));
    }

    @Override
    public T get(Object arg0) {
    return set.innerMap.get(Equivalence.identity().wrap(arg0));
    }

    private class IdentityLinkedHashMapEntry implements Entry<K, T> {

    private final Entry<Equivalence.Wrapper<K>, T> entry;

    public IdentityLinkedHashMapEntry(Entry<Equivalence.Wrapper<K>, T> entry) {
    this.entry = entry;
    }

    @Override
    public K getKey() {
    return entry.getKey().get();
    }

    @Override
    public T getValue() {
    return entry.getValue();
    }

    @Override
    public T setValue(T value) {
    return entry.setValue(value);
    }
    }

    private class IdentityLinkedHashSet extends AbstractSet<Entry<K, T>> {

    private final Map<Equivalence.Wrapper<K>, T> innerMap = new LinkedHashMap<>();

    @Override
    public Iterator<Entry<K, T>> iterator() {
    return Iterators.transform(innerMap.entrySet().iterator(), IdentityLinkedHashMapEntry::new);
    }

    @Override
    public boolean add(Entry<K, T> entry) {
    innerMap.put(Equivalence.identity().wrap(entry.getKey()), entry.getValue());
    return true;
    }

    @Override
    public int size() {
    return innerMap.size();
    }

    @Override
    public boolean contains(Object arg0) {
    return innerMap.containsKey(Equivalence.identity().wrap(arg0));
    }
    }
    }