Java中取多个集合的交集和并集

//取多个集合的交集
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 {

//只有一个集合则不取交集

for (List<String> list2 : list) {

for (String name : list2) {

set.add(name);

}

}

}

return set;

}

// 求多个集合的并集
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 {

//只有一个集合则直接插入结果

for (List<String> list2 : list) {

for (String name : list2) {

set.add(name);

}

}

}

return set;

}