作者：未知 来源：月光软件站 加入时间：2005-2-28　月光软件站

/**
 * @Author 陈伟兵
 * @Msn:[email protected]
 * @E-mail:[email protected]
 * @CreateTime 2004-11-30
 * @Version:1.0
 */
package com.cwbnig.util;

import java.util.Random;
import java.util.Iterator;

public class ArrayBag implements BagADT
{
    private static Random rand=new Random();
   
    private final int DEFAULT_CAPACITY =100;
   
    private final int NOT_FOUND=-1;
   
    private int count;
   
    private Object[] contents;
   
    /**
     * Create an empty bag using the default capacity
     */
    public ArrayBag()
    {
        count=0;
        contents=new Object[DEFAULT_CAPACITY];
    }
   
    /**
     * Create an empty bag using the specified capacity
     */
    public ArrayBag(int initialCapacity)
    {
        count=0;
        contents=new Object[initialCapacity];
    }
   
    /**
     * Returns the number of elements currentl in this bag
     */
    public int size()
    {
        return count;
    }
   
    /**
     * Returns true if this bag is empty and false otherwise
     */
    public boolean isEmpty()
    {
        return(count==0);
    }
   
    /**
     * Adds the speacified element to the bag,expanding the capacity of the array if necessary.
     */
    public void add(Object element)
    {
        if(size()==contents.length)
        {
            expandCapacity();
        }
        contents[count]=element;
        count++;
    }
   
    /**
     * Creates a new array to store the contents of the bag with twice the capcity of the old one.
     */
    public void expandCapacity()
    {
        Object[] larger=new Object[contents.length*2];
        for(int index=0;index<contents.length;index++)
        {
            larger[index]=contents[index];
        }
        contents=larger;
    }
   
    /**
     * Adds the contents of the parameter to this bag.
     */
    public void addAll(BagADT bag)
    {
        Iterator scan=bag.iterator();
        while(scan.hasNext())
        {
            add(scan.next());
        }
    }
   
    /**
     * Remove a random element from the bag and returns it.Throws and EmptyBagException if the bag is empty
     */
    public Object removeRandom()throws EmptyBagException
    {
        if(isEmpty())
        {
            throw new EmptyBagException();
        }
        int choice=rand.nextInt(count);
        Object result=contents[choice];
        contents[choice]=contents[count-1];
        contents[count-1]=null;
        count--;
        return result;
    }
   
    /**
     * Removes one occurance of the specified element from the bag and returns it.
     * Throws and EmptyBagException if the bag is empty and a NoSuchElementException if the target is not in the bag.
     */
    public Object remove(Object target)throws EmptyBagException,NoSuchElementException
    {
        int search=NOT_FOUND;
        if(isEmpty())
        {
            throw new EmptyBagException();
        }
        for(int index=0;index<count&&search==NOT_FOUND;index++)
        {
            search=index;
        }
        if(search==NOT_FOUND)
        {
            throw new NoSuchElementException();
        }
        Object result=contents[count-1];
        contents[search]=contents[count-1];
        contents[count-1]=null;
        return result;
    }
   
    /**
     * Returns a new bag that is the union of this bag and the parameter.
     */
    public BagADT union(BagADT bag)
    {
        ArrayBag both=new ArrayBag();
        for(int index=0;index<count;index++)
        {
            both.add(contents[index]);
        }
        Iterator scan=bag.iterator();
        while(scan.hasNext())
        {
            both.add(scan.next());
        }
        return both;
    }
   
    /**
     * Returns true if this bag contains the specified target element.
     */
    public boolean contains(Object target)
    {
        int search=NOT_FOUND;
        for(int index=0;index<count&&search==NOT_FOUND;index++)
        {
            if(contents[index].equals(target))
            {
                search=index;
            }
        }
        return(search!=NOT_FOUND);
    }
   
    /**
     * Returns true if this bag contains exactly the same elements as the parameter.
     */
    public boolean equals(BagADT bag)
    {
        boolean result=false;
        ArrayBag temp1=new ArrayBag();
        ArrayBag temp2=new ArrayBag();
        Object obj;
        if(size()==bag.size())
        {
            temp1.addAll(this);
            temp2.addAll(bag);
            Iterator scan=bag.iterator();
            while(scan.hasNext())
            {
                obj=scan.next();
                if(temp1.contains(obj))
                {
                    try
                    {
                        temp1.remove(obj);
                        temp2.remove(obj);
                    }
                    catch(EmptyBagException emptyE)
                    {
                        System.out.println("The current Bag is Empty!");
                    }
                    catch(NoSuchElementException nosuchE)
                    {
                        System.out.println("The current Bag has no such element!");
                    }
                }
            }
            result=(temp1.isEmpty()&&temp2.isEmpty());
        }
        return result;
    }
   
    /**
     * Returns an iterator for the elements currently in this bag
     */
    public Iterator iterator()
    {
        return new ArrayIterator(contents,count);
    }
   
    /**
     * Returns a string representation of this bag.
     */
    public String toString()
    {
        String result="";
        for(int index=0;index<count;index++)
        {
            result=result+contents[index].toString()+"\n";
        }
        return result;
    }
}

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