1 // Copyright 2000-2005 the Contributors, as shown in the revision logs.
2 // Licensed under the Apache Public Source License 2.0 ("the License").
3 // You may not use this file except in compliance with the License.
9 /** Implementation of an unsynchronized hash table, with one or two
10 * keys, using Radke's quadradic residue linear probing instead of
11 * buckets to minimize object count (less allocations, faster GC).
12 * See C. Radke, Communications of the ACM, 1970, 103-105
16 public class Hash implements java.io.Serializable {
18 public static final long serialVersionUID = 8177551301264350283L;
20 /** this object is inserted as key in a slot when the
21 * corresponding value is removed -- this ensures that the
22 * probing sequence for any given key remains the same even if
23 * other keys are removed.
25 // FIXME: this should have been static except that that makes it nonserializable
26 private Object placeholder = new java.io.Serializable() { };
28 /** the number of entries with at least one non-null key */
29 private int usedslots = 0;
31 /** the number of entries with non-null values */
32 protected int size = 0;
34 /** when num_slots < loadFactor * size, rehash into a bigger table */
35 private final int loadFactor;
38 private Object[] keys1 = null;
40 /** secondary keys; null if no secondary key has ever been added */
41 private Object[] keys2 = null;
43 /** the values for the table */
44 private Object[] vals = null;
46 /** the number of entries with a non-null value */
47 public int size() { return size; }
49 /** empties the table */
53 for(int i=0; i<vals.length; i++) {
56 if (keys2 != null) keys2[i] = null;
60 /** returns all the primary keys in the table */
61 public Enumeration keys() { return new HashEnum(); }
63 public Hash() { this(25, 3); }
64 public Hash(int initialcapacity, int loadFactor) {
65 // using a pseudoprime in the form 4x+3 ensures full coverage
66 initialcapacity = initialcapacity / 4;
67 initialcapacity = 4 * initialcapacity + 3;
68 keys1 = new Object[initialcapacity];
69 vals = new Object[initialcapacity];
70 this.loadFactor = loadFactor;
73 public void remove(Object k1) { remove(k1, null); }
74 public void remove(Object k1, Object k2) { put_(k1, k2, null); }
76 private void rehash() {
77 Object[] oldkeys1 = keys1;
78 Object[] oldkeys2 = keys2;
79 Object[] oldvals = vals;
80 keys1 = new Object[oldvals.length * 2];
81 keys2 = oldkeys2 == null ? null : new Object[oldvals.length * 2];
82 vals = new Object[oldvals.length * 2];
85 for(int i=0; i<oldvals.length; i++)
86 if (((oldkeys1[i] != null && oldkeys1[i] != placeholder) || (oldkeys2 != null && oldkeys2[i] != null)) && oldvals[i] != null)
87 put_(oldkeys1[i], oldkeys2 == null ? null : oldkeys2[i], oldvals[i]);
90 public Object get(Object k1) { return get(k1, null); }
91 public Object get(Object k1, Object k2) {
92 if (k2 != null && keys2 == null) return null;
93 int hash = (k1 == null ? 0 : k1.hashCode()) ^ (k2 == null ? 0 : k2.hashCode());
94 int dest = Math.abs(hash) % vals.length;
98 while (keys1[dest] != null || (keys2 != null && keys2[dest] != null)) {
99 Object hk1 = keys1[dest];
100 Object hk2 = keys2 == null ? null : keys2[dest];
101 if ((k1 == hk1 || (k1 != null && hk1 != null && k1.equals(hk1))) &&
102 (k2 == hk2 || (k2 != null && hk2 != null && k2.equals(hk2)))) {
105 dest = Math.abs((odest + (plus ? 1 : -1 ) * tries * tries) % vals.length);
112 public void put(Object k1, Object v) { put(k1, null, v); }
113 public void put(Object k1, Object k2, Object v) { put_(k1, k2, v); }
114 private void put_(Object k1, Object k2, Object v) {
115 if (usedslots * loadFactor > vals.length) rehash();
116 int hash = (k1 == null ? 0 : k1.hashCode()) ^ (k2 == null ? 0 : k2.hashCode());
117 int dest = Math.abs(hash) % vals.length;
122 Object hk1 = keys1[dest];
123 Object hk2 = keys2 == null ? null : keys2[dest];
124 if (hk1 == null && hk2 == null) { // empty slot
125 if (v == null) return;
131 if ((k1 == hk1 || (k1 != null && hk1 != null && k1.equals(hk1))) && // replacing former entry
132 (k2 == hk2 || (k2 != null && hk2 != null && k2.equals(hk2)))) {
134 // we don't actually remove things from the table; rather, we insert a placeholder
143 dest = Math.abs((odest + (plus ? 1 : -1 ) * tries * tries) % vals.length);
149 if (k2 != null && keys2 == null) keys2 = new Object[keys1.length];
150 if (keys2 != null) keys2[dest] = k2;
154 private class HashEnum implements java.util.Enumeration {
155 private int iterator = 0;
156 private int found = 0;
158 public boolean hasMoreElements() {
159 return found < usedslots;
162 public Object nextElement() {
163 if (!hasMoreElements()) throw new java.util.NoSuchElementException();
166 while (o == null) o = keys1[iterator++];
167 if (o == null) throw new IllegalStateException("Didn't find an element, when I should have.");