Open Locker1995 opened 6 years ago
这份来自JDK 8 Collections.copy()源码,给我们提供了一个案例
/**
* Copies all of the elements from one list into another. After the
* operation, the index of each copied element in the destination list
* will be identical to its index in the source list. The destination
* list must be at least as long as the source list. If it is longer, the
* remaining elements in the destination list are unaffected. <p>
*
* This method runs in linear time.
*
* @param <T> the class of the objects in the lists
* @param dest The destination list.
* @param src The source list.
* @throws IndexOutOfBoundsException if the destination list is too small
* to contain the entire source List.
* @throws UnsupportedOperationException if the destination list's
* list-iterator does not support the <tt>set</tt> operation.
*/
public static <T> void copy(List<? super T> dest, List<? extends T> src) {
int srcSize = src.size();
if (srcSize > dest.size())
throw new IndexOutOfBoundsException("Source does not fit in dest");
if (srcSize < COPY_THRESHOLD ||
(src instanceof RandomAccess && dest instanceof RandomAccess)) {
for (int i=0; i<srcSize; i++)
dest.set(i, src.get(i));
} else {
ListIterator<? super T> di=dest.listIterator();
ListIterator<? extends T> si=src.listIterator();
for (int i=0; i<srcSize; i++) {
di.next();
di.set(si.next());
}
}
}
贴上昨天在虎牙笔试遇到的范题(记得不是很清楚了) 请选出正确的操作 A.List<? extends Object> list = new ArrayList<>(); list.add(new Object()); B.List<? extends Number> list = new ArrayList<>(); list.add(4.0); C.List<? super Number> list = new ArrayList<>();list.add(4.0); D..... 还有一个忘了,题目的主要意思就是考泛型。
链接转自知乎
这个是我个人认为一个很好的帖子去解释这个问题 https://www.zhihu.com/question/20400700