{
+ /**
+ * The minimum capacity, used if a lower value is implicitly specified.
+ * The value 2 corresponds to an expected maximum size of 1,
+ * given a load factor of 2/3. MUST be a power of two.
+ */
+ private static final int MINIMUM_CAPACITY = 2;
+
+ /**
+ * The maximum capacity.
+ *
+ * In fact, the HashArray can hold no more than MAXIMUM_CAPACITY-1 elements
+ * because it has to have at least one slot == null
+ * in order to avoid infinite loops in get() and put().
+ */
+ private static final int MAXIMUM_CAPACITY = 1 << 30;
+
+ /**
+ * The table, re-sized as necessary.
+ * Length MUST always be a power of two.
+ */
+ private T[] table;
+
+ /**
+ * The number of elements contained in this HashArray.
+ */
+ private int size;
+
+ /**
+ * Constructor with {@code expectedSize} pre-allocates the
+ * {@link #table}.
+ *
+ * @param expectedMaxSize expected number of elements new HashArray
+ * will hold.
+ */
+ @SuppressWarnings("unchecked")
+ public HashArray(int expectedMaxSize) {
+ if (expectedMaxSize < 0)
+ throw new IllegalArgumentException("expectedMaxSize is negative: "
+ + expectedMaxSize);
+ table = (T[]) new Object[capacity(expectedMaxSize)];
+ }
+
+ /**
+ * Returns the appropriate capacity for the given expected maximum size.
+ * Returns the smallest power of two between MINIMUM_CAPACITY and
+ * MAXIMUM_CAPACITY, inclusive, that is greater than (3 *
+ * expectedMaxSize)/2, if such a number exists. Otherwise returns
+ * MAXIMUM_CAPACITY.
+ */
+ private static int capacity(int expectedMaxSize) {
+ // assert expectedMaxSize >= 0;
+ return
+ (expectedMaxSize > MAXIMUM_CAPACITY / 3) ? MAXIMUM_CAPACITY :
+ (expectedMaxSize <= 2 * MINIMUM_CAPACITY / 3) ? MINIMUM_CAPACITY :
+ Integer.highestOneBit(expectedMaxSize + (expectedMaxSize << 1));
+ }
+
+ /**
+ * Returns a hash code value for an element of this HashArray or a
+ * lookup object.
+ *
+ * By default it returns:
+ *
+ * obj.{@link Object#hashCode() hashCode()}
+ *
+ * But can be overridden in subclasses.
+ *
+ * @param obj an element of this HashArray or a lookup object
+ * @return a hash code value for an element or lookup object.
+ * @see #equals(Object, Object)
+ */
+ protected int hashCode(Object obj) {
+ return obj.hashCode();
+ }
+
+ /**
+ * Indicates whether an element of this HashArray is "equal to"
+ * a lookup object or another element.
+ *
+ * By default it returns:
+ *
+ * element.{@link Object#equals(Object) equals(obj)}
+ *
+ * But can be overridden in subclasses.
+ *
+ * @param element an element of this HashArray
+ * @param obj a lookup object or another element
+ * @return {@code true} if an element is the same
+ * as a lookup object or another element;
+ * {@code false} otherwise.
+ * @see #hashCode(Object)
+ */
+ protected boolean equals(T element, Object obj) {
+ return element.equals(obj);
+ }
+
+ /**
+ * Returns index for Object x.
+ */
+ private int hash(Object x, int length) {
+ int h = hashCode(x);
+ return (h ^ (h >>> 16)) & (length - 1);
+ }
+
+ /**
+ * Circularly traverses table of size length (which is a power of 2).
+ */
+ private static int nextKeyIndex(int i, int length) {
+ return (i + 1) & (length - 1);
+ }
+
+ /**
+ * @return Number of elements contained in this HashArray.
+ */
+ public int size() {
+ return size;
+ }
+
+ /**
+ * @param lookupObj a non-null lookup object
+ * @return The element which is equal to specified {@code lookupObj}
+ * if it exists in this HashArray or null if it doesn't.
+ * (There can be at most one such element.)
+ * @throws NullPointerException if {@code lookupObj} is null
+ */
+ @SuppressWarnings("unchecked")
+ public T get(Object lookupObj) {
+ if (lookupObj == null) throw new NullPointerException();
+ final T[] tab = table;
+ int i = hash(lookupObj, tab.length);
+ while (true) {
+ T element = tab[i];
+ if (element == null) {
+ return null;
+ }
+ if (equals(element, lookupObj)) {
+ return element;
+ }
+ i = nextKeyIndex(i, tab.length);
+ }
+ }
+
+ /**
+ * Adds {@code newElement} if an element equal to it is not present in
+ * this HashArray and returns null, or returns the existing element and
+ * replaces it with {@code newElement} if such element is present.
+ *
+ * @param newElement new element to put into this HashArray
+ * @return previous element if there was one or null if there was none
+ */
+ public T put(T newElement) {
+ return put(newElement, true);
+ }
+
+ /**
+ * Adds {@code newElement} if an element equal to it is not present in
+ * this HashArray and returns null, or returns the existing element and
+ * doesn't modify HashArray if such element is present.
+ *
+ * @param newElement new element to put into this HashArray
+ * @return previous element if there was one or null if there was none
+ */
+ public T putIfAbsent(T newElement) {
+ return put(newElement, false);
+ }
+
+ private T put(T newElement, boolean replace) {
+ if (newElement == null) throw new NullPointerException();
+ for (; ; ) {
+ final T[] tab = table;
+ int i = hash(newElement, tab.length);
+
+ for (
+ T element; (element = tab[i]) != null;
+ i = nextKeyIndex(i, tab.length)
+ ) {
+ if (equals(element, newElement)) {
+ if (replace) {
+ tab[i] = newElement;
+ }
+ return element;
+ }
+ }
+
+ final int s = size + 1;
+ // Use optimized form of 3 * s / 2.
+ // Next capacity is 2 * current capacity.
+ if (s + (s >> 1) > tab.length && resize(tab.length << 1))
+ continue;
+
+ tab[i] = newElement;
+ size = s;
+ return null;
+ }
+ }
+
+ /**
+ * Resizes the table if necessary to hold given capacity.
+ */
+ private boolean resize(int newLength) {
+ T[] oldTable = table;
+ int oldLength = oldTable.length;
+ if (oldLength == MAXIMUM_CAPACITY) { // can't expand any further
+ if (size == MAXIMUM_CAPACITY - 1)
+ throw new IllegalStateException("Capacity exhausted.");
+ return false;
+ }
+ if (oldLength >= newLength)
+ return false;
+
+ @SuppressWarnings("unchecked")
+ T[] newTable = (T[]) new Object[newLength];
+
+ for (int j = 0; j < oldLength; j++) {
+ T element = oldTable[j];
+ if (element != null) {
+ oldTable[j] = null;
+ int i = hash(element, newLength);
+ while (newTable[i] != null)
+ i = nextKeyIndex(i, newLength);
+ newTable[i] = element;
+ }
+ }
+ table = newTable;
+ return true;
+ }
+
+ /**
+ * Removes the element equal to {@code lookupObj} and
+ * returns it if present or returns null if not present.
+ *
+ * @param lookupObj a non-null lookup object
+ * @return the removed element if there was one or null if
+ * there was none
+ * @throws NullPointerException if {@code lookupObj} is null
+ */
+ public T remove(Object lookupObj) {
+ if (lookupObj == null) throw new NullPointerException();
+ T[] tab = table;
+ int i = hash(lookupObj, tab.length);
+
+ while (true) {
+ T element = tab[i];
+ if (element == null) {
+ return null;
+ }
+ if (equals(element, lookupObj)) {
+ size--;
+ tab[i] = null;
+ closeDeletion(tab, i);
+ return element;
+ }
+ i = nextKeyIndex(i, tab.length);
+ }
+ }
+
+ /**
+ * Rehash all possibly-colliding elements following a
+ * deletion. This preserves the linear-probe
+ * collision properties required by get, putIfAbsent, remove.
+ *
+ * @param d the index of a newly empty deleted slot
+ */
+ private void closeDeletion(Object[] tab, int d) {
+ // Adapted from Knuth Section 6.4 Algorithm R
+
+ // Look for elements to swap into newly vacated slot
+ // starting at index immediately following deletion,
+ // and continuing until a null slot is seen, indicating
+ // the end of a run of possibly-colliding elements.
+ Object element;
+ for (
+ int i = nextKeyIndex(d, tab.length); (element = tab[i]) != null;
+ i = nextKeyIndex(i, tab.length)
+ ) {
+ // The following test triggers if the element at slot i (which
+ // hashes to be at slot r) should take the spot vacated by d.
+ // If so, we swap it in, and then continue with d now at the
+ // newly vacated i. This process will terminate when we hit
+ // the null slot at the end of this run.
+ // The test is messy because we are using a circular table.
+ int r = hash(element, tab.length);
+ if ((i < r && (r <= d || d <= i)) || (r <= d && d <= i)) {
+ tab[d] = element;
+ tab[i] = null;
+ d = i;
+ }
+ }
+ }
+
+ /**
+ * Removes all of the elements from this HashArray.
+ */
+ public void clear() {
+ Arrays.fill(table, null);
+ size = 0;
+ }
+}