1.CollectionUtils.diff(Collection c1, Collection c2),返回集合c2不包含集合c1的元素
public static void main(String[] args) {
List<String> list1 = new ArrayList<String>();
list1.add("1");
list1.add("2");
List<String> list2 = new ArrayList<>();
list2.add("1");
list2.add("3");
list2.add("4");
Collection diff1 = CollectionUtils.diff(list1, list2);
System.out.println(diff1.toString());
Collection diff2 = CollectionUtils.diff(list2, list1);
System.out.println(diff2.toString());
Collection sameElement = CollectionUtils.diff(list1, diff1);
System.out.println(sameElement);
}
public static <T> Collection<T> diff(Collection<T> c1, Collection<T> c2) {
if (c1 != null && c1.size() != 0 && c2 != null && c2.size() != 0) {
Collection<T> difference = new ArrayList();
Iterator i$ = c1.iterator();
while(i$.hasNext()) {
T item = i$.next();
if (!c2.contains(item)) {
difference.add(item);
}
}
return difference;
} else {
return c1;
}
}
2.集合的removeAll(Collection<?> c)方法:将容器中所有包含集合c的元素移除
public static void main(String[] args) {
List<String> list1 = new ArrayList<String>();
list1.add("1");
list1.add("2");
List<String> list2 = new ArrayList<>();
list2.add("1");
list2.add("3");
list2.add("4");
Collection diffResult = new ArrayList(list2);
Collection sameResult = new ArrayList(list2);
diffResult.removeAll(list1);
System.out.println(diffResult);
sameResult.removeAll(diffResult);
System.out.println(sameResult);
}
public boolean removeAll(Collection<?> c) {
Objects.requireNonNull(c);
boolean modified = false;
for (Iterator<Map.Entry<K,V>> i = iterator(); i.hasNext(); ) {
if (c.contains(i.next())) {
i.remove();
modified = true;
}
}
return modified;
}
3.如果是直接判断两个集合是否有相同数据,可用Collections.disjoint(Collection<?> c1, Collection<?> c2)
if (Collections.disjoint(list1, list2)) {
System.out.println("有相同的元素");
}else{
System.out.println("没有相同的元素");
}