List集合类
Returns the hash code value for this list. The hash code of a list
* is defined to be the result of the following calculation:
* <pre>{@code
* int hashCode = 1;
* for (E e : list)
* hashCode = 31*hashCode + (e==null ? 0 : e.hashCode());
* }</pre>
可以看到，如果集合里面的值相同，那么集合对象equals会返回true！
Set集合类
* Returns the hash code value for this set. The hash code of a set is
* defined to be the sum of the hash codes of the elements in the set
可以看到，如果集合里面的值相同，那么集合对象equals会返回true！
Map集合类
* Returns the hash code value for this map. The hash code of a map is
* defined to be the sum of the hash codes of each entry in the map's
* Returns the hash code value for this map entry. The hash code
* of a map entry <tt>e</tt> is defined to be: <pre>
* (e.getKey()==null ? 0 : e.getKey().hashCode()) ^
* (e.getValue()==null ? 0 : e.getValue().hashCode())
可以看到，如果key和key相同、value和value相同，那么集合对象equals会返回true！
通过上面可以知道，集合类重写了equals方法，比较的是元素的hashcode值，只要集合类中元素的值相同，那么两个集合类的equals方法就会返回true！
