java 手工实现HashSet

底层是用HashMap来实现

HashMap map;
	private static final int VALUE=10;
	public test()
	{
		map=new HashMap();
	}

public void add(Object obs)     //将输入的值作为HashMap的键，从而达到不重复
{
	map.put(obs, VALUE);
}
public int size()
{
	return map.size();
}

public String toString()
{
	StringBuilder ss=new StringBuilder();
	for(Object s:map.keySet())
	{
		ss.append(s+",");
	}
	ss.setCharAt(ss.length()-1, ' ');
	return ss.toString();
}