Hash实现（散列表）

package Hash;import java.util.ConcurrentModificationException;import java.util.NoSuchElementException;import 算法.Collection;import 算法.Iterator;/*散列表 * 使用拉链法实现 */public class Hash<T> implements Collection<T> {private Entry[] table;                                                 //散列表数组private int hashTableSize;//散列表的大小private final double MAX_LOAD_FACTOR = 0.75;//再散列边界的百分比private int tableThreshold;//在散列的值private int modCount;//增删改操作加一public Hash(){table = new Entry[17];hashTableSize = 0;tableThreshold = (int)(table.length*MAX_LOAD_FACTOR);}//向散列表中添加值public boolean add(T item){int hashValue = item.hashCode()&Integer.MAX_VALUE;int index = hashValue % table.length;Entry<T> entry;entry = table[index];//判断节点是否已存在，并查找最后一个节点while(entry != null){//已经存在if(entry.value.equals(item)){return false;}//end ifentry = entry.next;}//end whilemodCount++;//新的元素作为头节点entry = new Entry<T>(item, hashValue, (Entry)table[index]);table[index] = entry;hashTableSize ++;//当当前表的数据大于表容量的75%时，再散列if(hashTableSize >= tableThreshold){rehash(hashTableSize * 2 + 1);}return true;}//end addprivate void rehash(int newTableSize){Entry[] newTbale = new Entry[newTableSize],   oldTable = table;Entry<T> entry,nextEntry;int index;for(int i = 0; i < table.length; i++){entry = table[i];if(entry != null){do{nextEntry = entry.next;index = entry.hashValue % newTableSize;//插入第一个位置entry.next = newTbale[index];newTbale[index] = entry;entry = nextEntry;}while(entry != null);}//end iftable = newTbale;tableThreshold =(int)(table.length * MAX_LOAD_FACTOR);oldTable = null;}//end for}//end rehash//删除节点public boolean remove(Object item){int index = (item.hashCode()&Integer.MAX_VALUE) % table.length;Entry<T> curr,prev;curr = table[index];prev = null;while(curr != null){if(curr.value.equals(item)){modCount++;//要删除的是第一个元素if(prev != null){prev.next = curr.next;}else{table[index] = curr.next;}hashTableSize --;return true;}//end ifelse{prev =curr;curr = curr.next;}}//end whilereturn false;}//end remove()//迭代器实现private class IteratorImpl implements Iterator<T>{Entry<T> next;                //写一个要遍历的节点int index;                         //索引int expctedModCount;    //保持单操作T lastReturend;                //返回值public IteratorImpl() {int i = 0;Entry<T> n = null;expctedModCount = modCount;if(hashTableSize != 0){while(i < table.length && ((n = table[i]) == null)){i++;}next = n;index = i;lastReturend = null;}//end if}public boolean hasNext() {return next != null;}public T next() {if(modCount != expctedModCount){throw new ConcurrentModificationException();}Entry<T> entry = next;if(entry == null){throw new NoSuchElementException();}lastReturend = entry.value;Entry<T> n = entry.next;int i = index;if(n == null){i++;while(i < table.length && (n = table[i] )== null){i++;}}index = i;next = n;return lastReturend;}//end next()public void remove() {if(lastReturend == null){throw new IllegalStateException();}if(modCount != expctedModCount){throw new ConcurrentModificationException();}Hash.this.remove(lastReturend);expctedModCount = modCount;lastReturend = null;}}//散列表的内部节点private static class Entry<T>{T value;                     //值int hashValue;          //hash值Entry<T> next;         //下一个节点Entry(T value, int hashValue , Entry<T> next){this.value = value;this.hashValue = hashValue;this.next = next;}}public void clear() {// make all hash table entries nullfor (int i=0;i < table.length;i++)table[i] = null;// we have modified the hash table, and it has// no entriesmodCount++;hashTableSize = 0;}public boolean contains(Object item) {// compute the hash table indexint index = (item.hashCode() & Integer.MAX_VALUE) % table.length;Entry entry;// entry references the front of a linked list of colliding// valuesentry = table[index];// scan the linked list and return true if item is in listwhile (entry != null){if (entry.value.equals(item))return true;entry = entry.next;}return false;}public boolean isEmpty() {return hashTableSize == 0 ;}@Overridepublic Iterator<T> iterator() {return new IteratorImpl();}public int size() {return hashTableSize;}public Object[] toArray() {// allocate the array an an iteratorObject[] arr = new Object[hashTableSize];Iterator<T> iter = iterator();int i = 0;// iterate the hash table and assign its// values into the arraywhile (iter.hasNext()){arr[i] = iter.next();i++;}return arr;}//toStringpublic String toString(){int max = hashTableSize - 1;StringBuffer buf = new StringBuffer();Iterator<T> iter = iterator();buf.append("[");for (int i = 0; i <= max; i++){buf.append(iter.next());    if (i < max)buf.append(", ");}buf.append("]");return buf.toString();}}