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• LinkedHashTreeMap.java

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com.google.gson.internal.LinkedHashTreeMap Maven / Gradle / Ivy

/*
 * Copyright (C) 2010 The Android Open Source Project
 * Copyright (C) 2012 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.gson.internal;

import java.io.IOException;
import java.io.InvalidObjectException;
import java.io.ObjectInputStream;
import java.io.ObjectStreamException;
import java.io.Serializable;
import java.util.AbstractMap;
import java.util.AbstractSet;
import java.util.Arrays;
import java.util.Comparator;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.NoSuchElementException;
import java.util.Set;

/**
 * A map of comparable keys to values. Unlike {@code TreeMap}, this class uses
 * insertion order for iteration order. Comparison order is only used as an
 * optimization for efficient insertion and removal.
 *
 * 
This implementation was derived from Android 4.1's TreeMap and
 * LinkedHashMap classes.
 */
public final class LinkedHashTreeMap extends AbstractMap implements Serializable {
  @SuppressWarnings({ "unchecked", "rawtypes" }) // to avoid Comparable>>
  private static final Comparator NATURAL_ORDER = new Comparator() {
    public int compare(Comparable a, Comparable b) {
      return a.compareTo(b);
    }
  };

  Comparator comparator;
  Node[] table;
  final Node header;
  int size = 0;
  int modCount = 0;
  int threshold;

  /**
   * Create a natural order, empty tree map whose keys must be mutually
   * comparable and non-null.
   */
  @SuppressWarnings("unchecked") // unsafe! this assumes K is comparable
  public LinkedHashTreeMap() {
    this((Comparator) NATURAL_ORDER);
  }

  /**
   * Create a tree map ordered by {@code comparator}. This map's keys may only
   * be null if {@code comparator} permits.
   *
   * @param comparator the comparator to order elements with, or {@code null} to
   *     use the natural ordering.
   */
  @SuppressWarnings({ "unchecked", "rawtypes" }) // unsafe! if comparator is null, this assumes K is comparable
  public LinkedHashTreeMap(Comparator comparator) {
    this.comparator = comparator != null
        ? comparator
        : (Comparator) NATURAL_ORDER;
    this.header = new Node();
    this.table = new Node[16]; // TODO: sizing/resizing policies
    this.threshold = (table.length / 2) + (table.length / 4); // 3/4 capacity
  }

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

  @Override public V get(Object key) {
    Node node = findByObject(key);
    return node != null ? node.value : null;
  }

  @Override public boolean containsKey(Object key) {
    return findByObject(key) != null;
  }

  @Override public V put(K key, V value) {
    if (key == null) {
      throw new NullPointerException("key == null");
    }
    Node created = find(key, true);
    V result = created.value;
    created.value = value;
    return result;
  }

  @Override public void clear() {
    Arrays.fill(table, null);
    size = 0;
    modCount++;

    // Clear all links to help GC
    Node header = this.header;
    for (Node e = header.next; e != header; ) {
      Node next = e.next;
      e.next = e.prev = null;
      e = next;
    }

    header.next = header.prev = header;
  }

  @Override public V remove(Object key) {
    Node node = removeInternalByKey(key);
    return node != null ? node.value : null;
  }

  /**
   * Returns the node at or adjacent to the given key, creating it if requested.
   *
   * @throws ClassCastException if {@code key} and the tree's keys aren't
   *     mutually comparable.
   */
  Node find(K key, boolean create) {
    Comparator comparator = this.comparator;
    Node[] table = this.table;
    int hash = secondaryHash(key.hashCode());
    int index = hash & (table.length - 1);
    Node nearest = table[index];
    int comparison = 0;

    if (nearest != null) {
      // Micro-optimization: avoid polymorphic calls to Comparator.compare().
      @SuppressWarnings("unchecked") // Throws a ClassCastException below if there's trouble.
      Comparable