Java迭代器类型转换为hashmap值 [英] Java iterator type casting in hashmap values
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问题描述
为什么我们需要在Java中输入caste Iterator?例如: -
Why do we need to type caste Iterator in Java? For example:-
HashMap<Integer,Integer> hm = new HashMap<Integer,Integer>();
hm.put(1,3);
hm.put(2,6);
hm.put(3,7);
Iterator it = hm.values().iterator();
while(it.hasNext())
{
ans += it.next(); // Raises an error
}
但如果我更新我的错误代码:
But if I update my code to:
Iterator<Integer> it = hm.values().iterator();// works fine
为什么迭代器没有将hm.values()类型转换为整数?
我尝试过:
在Java中迭代hashmap.values()
Why is iterator not type casting hm.values() to integer?
What I have tried:
Iterating over hashmap.values() in Java
推荐答案
Iterator
需要知道它要处理的对象,就像HashMap $ c一样$ c>需要知道。如果未指定类型,则
Iterator
将在下一次调用时返回
,然后需要转换为真实类型。对象
( )
TheIterator
needs to know what objects it is to deal with, in the same way that theHashMap
needs to know. If the type is not specified then theIterator
returns anobject
on a call tonext()
, which then needs to be cast to its real type.
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