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();
}