Hash實現（散列表）

package Hash;

import java.util.ConcurrentModificationException;
import java.util.NoSuchElementException;


import 算法.Collection;
import 算法.Iterator;

/*散列表
 * 使用拉鍊法實現
 */
public class Hash<T> implements Collection<T> {
	private Entry[] table;                                                 //散列表數組
	private int hashTableSize;										//散列表的大小
	private final double MAX_LOAD_FACTOR = 0.75;		//再散列邊界的百分比
	private int tableThreshold;										//在散列的值
	private int modCount;												//增刪改操作加一
	
	
	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];
		
		//判斷節點是否已存在，並查找最後一個節點
		while(entry != null){
			//已經存在
			if(entry.value.equals(item)){
				return false;
			}//end if
			entry = entry.next;
		}//end while
		
		modCount++;
		//新的元素作爲頭節點
		entry = new Entry<T>(item, hashValue, (Entry)table[index]);
		table[index] = entry;
		hashTableSize ++;
		
		//噹噹前表的數據大於表容量的75%時，再散列
		if(hashTableSize >= tableThreshold){
			rehash(hashTableSize * 2 + 1);
		}
		return true;
	}//end add
	
	private 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;
					//插入第一個位置
					entry.next = newTbale[index];
					newTbale[index] = entry;
					
					entry = nextEntry;
				}while(entry != null);
			}//end if
			table = newTbale;
			tableThreshold =(int)(table.length * MAX_LOAD_FACTOR);
			oldTable = null;
		}//end for
	}//end rehash
	
	//刪除節點
	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++;
				//要刪除的是第一個元素
				if(prev != null){
					prev.next = curr.next;
				}
				else{
					table[index] = curr.next;
				}
				hashTableSize --;
				return true;
			}//end if
			else{
				prev =curr;
				curr = curr.next;
			}
		}//end while
		return false;
	}//end remove()
	
	//迭代器實現
	private class IteratorImpl implements Iterator<T>{
		Entry<T> next;                //寫一個要遍歷的節點
		int index;                         //索引
		int expctedModCount;    //保持單操作
		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;
		}
		
	}
	
	//散列表的內部節點
	private static class Entry<T>{
		T value;                     //值
		int hashValue;          //hash值
		Entry<T> next;         //下一個節點
		
		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 null
		for (int i=0;i < table.length;i++)
			table[i] = null;

		// we have modified the hash table, and it has
		// no entries
		modCount++;
		hashTableSize = 0;
		
	}
	
	public boolean contains(Object item) {
		// compute the hash table index
		int index = (item.hashCode() & Integer.MAX_VALUE) % table.length;
		Entry entry;

		// entry references the front of a linked list of colliding
		// values
		entry = table[index];

		// scan the linked list and return true if item is in list
		while (entry != null)
		{
			if (entry.value.equals(item))
				return true;
			entry = entry.next;
		}

		return false;		
	}

	public boolean isEmpty() {
		return hashTableSize == 0 ;
	}

	@Override
	public Iterator<T> iterator() {
		return new IteratorImpl();
	}

	public int size() {
		return hashTableSize;
	}

	public Object[] toArray() {
		// allocate the array an an iterator
		Object[] arr = new Object[hashTableSize];
		Iterator<T> iter = iterator();
		int i = 0;

		// iterate the hash table and assign its
		// values into the array
		while (iter.hasNext())
		{
			arr[i] = iter.next();
			i++;
		}

		return arr;
	}
	
	//toString
	public 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();
	}

}