Java中取多個集合的交集和並集__Java

//取多個集合的交集
private Set<String> getIntersection(List<List<String>> list ) {
Set<String> set = new HashSet<String>();
int size = list.size();
if(size > 1){
//取集合中的交集 for (int i = 0; i < size; i++) { int j = i+1; if(j < size ){ list.get(0).retainAll(list.get(j));  if(i == size - 2){ List<String> resultList = list.get(0); for (String name : resultList) { set.add(name); } } } } }else {
//只有一個集合則不取交集 for (List<String> list2 : list) { for (String name : list2) { set.add(name); } } }

return set;

}

// 求多個集合的並集
private Set<String> getUnion(List<List<String>> list) {

Set<String> set = new HashSet<String>();

if(list == null){list = new ArrayList<List<String>>();}

int size = list.size();

if(size > 1){

for (int i = 0; i < size; i++) {

int j = i+1;

if(j < size ){

list.get(0).removeAll(list.get(j)); 

list.get(0).addAll(list.get(j)); 

if(i == size - 2){

List<String> resultList = list.get(0);

for (String name : resultList) {

set.add(name);

}

}

}

}

}else {

//只有一個集合則直接插入結果

for (List<String> list2 : list) {

for (String name : list2) {

set.add(name);

}

}

}

return set;

}