我想做的事情似乎很简单:计算一组集合的大小总和。Netbeans给出以下警告/错误:
actual argument java.util.ArrayList<java.util.TreeSet<java.lang.Integer>> cannot be converted to java.util.List<java.util.Set<java.lang.Object>> by method invocation conversion
对于以下两段代码:
/**
* Sums the sizes of all sets in a list. Note that while there will be
* no duplicate elements in a single set, "sister" sets may contain
* elements, so the value returned is **not** equal to the number of unique
* elements in all sets.
* @param list, a List of Sets
* @return the number of elements contained in all sets
*/
public static int sizeOfListOfSets(List<Set<Object>> list) {
int size = 0;
for (Set<Object> set : list) {
size += set.size();
}
return size;
}
然后使用以下代码调用它:
ArrayList<TreeSet<Integer>> testList = new ArrayList<TreeSet<Integer>>();
TreeSet<Integer> testSet;
int size = 0;
testSet = new TreeSet<Integer>();
testSet.add(new Integer(++size));
testSet.add(new Integer(++size));
testList.add(testSet);
testSet = new TreeSet<Integer>();
testSet.add(new Integer(++size));
testList.add(testSet);
int expResult = size;
int result = Helpers.sizeOfListOfSets(testList);
最后一行出现编译错误:
error: method sizeOfListOfSets in class Helpers cannot be applied to given types;
1 error
那么,为什么不能将 java.lang.Integer 转换为 java.lang.Object?
ArrayList<TreeSet<Integer>>
转换为List<Set<Object>>
?” - Kirk Woll