判断一个对象是否为空

Java程序中判断一个对象是否为空的一个小总结

public static <T> T requireNonNull(T obj, String message) {
		if (obj == null)
		{
			 throw new NullPointerException(message);
		}
		else if(obj instanceof Collection)
        {
        	Collection<?> newObj = (Collection<?>)obj;
        	if(newObj.isEmpty())
        	{
        		throw new NullPointerException(message);
        	}else{
        		if(newObj.size()==1)
        		{
        			Iterator iterator = newObj.iterator();
        			while(iterator.hasNext())
        			{
        				Object value = iterator.next();
        				if(value == null)
        				{
        					throw new NullPointerException(message);
        				}
        			}
        		}
        	}
        }else if(obj instanceof Map)
        {
        	Map<?, ?> newObj = (Map<?, ?>)obj;
        	if(newObj.isEmpty())
        	{
        		throw new NullPointerException(message);
        	}
        }
		return 	obj;
    }