一、jdk1.8以下版本
1、Collections.disjoint()
1.1、方法在java.util包中。
1.2、用于检查给定的 Collection 对象是否可能包含任何公共元素；不存在公共元素时返回true，否则返回false。
public static boolean disjoint(Collection cl1, Collection cl2);
1.3、代码块
public static boolean disjoint(Collection<?> c1, Collection<?> c2) {// The collection to be used for contains(). Preference is given to// the collection who's contains() has lower O() complexity.Collection<?> contains = c2;// The collection to be iterated. If the collections' contains() impl// are of different O() complexity, the collection with slower// contains() will be used for iteration. For collections who's// contains() are of the same complexity then best performance is// achieved by iterating the smaller collection.Collection<?> iterate = c1;// Performance optimization cases. The heuristics:// 1. Generally iterate over c1.// 2. If c1 is a Set then iterate over c2.// 3. If either collection is empty then result is always true.// 4. Iterate over the smaller Collection.if (c1 instanceof Set) {// Use c1 for contains as a Set's contains() is expected to perform// better than O(N/2)iterate = c2;contains = c1;} else if (!(c2 instanceof Set)) {// Both are mere Collections. Iterate over smaller collection.// Example: If c1 contains 3 elements and c2 contains 50 elements and// assuming contains() requires ceiling(N/2) comparisons then// checking for all c1 elements in c2 would require 75 comparisons// (3 * ceiling(50/2)) vs. checking all c2 elements in c1 requiring// 100 comparisons (50 * ceiling(3/2)).int c1size = c1.size();int c2size = c2.size();if (c1size == 0 || c2size == 0) {// At least one collection is empty. Nothing will match.return true;}if (c1size > c2size) {iterate = c2;contains = c1;}}for (Object e : iterate) {if (contains.contains(e)) {// Found a common element. Collections are not disjoint.return false;}}// No common elements were found.return true;}
1.4、用法
public static void main(String[] args) {List<Integer> aa = new ArrayList<>();aa.add(1001);aa.add(1002);List<Integer> bb = new ArrayList<>();bb.add(1001);bb.add(1002);Set<Integer> cc = new HashSet<>();Set<Integer> dd = new HashSet<>();dd.add(1);dd.add(2);//当 Collection 对象中不存在公共元素时返回真，否则返回假System.out.println( Collections.disjoint(aa,bb));//falseSystem.out.println( Collections.disjoint(cc,dd));//true}
2、CollectionUtils.containsAny()
2.1、方法在mons.collections.CollectionUtils中。
2.2、用于检查给定的 Collection 对象是否可能包含任何公共元素；存在公共元素时返回true，否则返回false。
public static boolean containsAny(Collection coll1, Collection coll2);
2.3、代码块
public static boolean containsAny(Collection coll1, Collection coll2) {Iterator it;if (coll1.size() < coll2.size()) {it = coll1.iterator();while(it.hasNext()) {if (coll2.contains(it.next())) {return true;}}} else {it = coll2.iterator();while(it.hasNext()) {if (coll1.contains(it.next())) {return true;}}}return false;}
2.4、用法
public static void main(String[] args) {List<Integer> aa = new ArrayList<>();aa.add(1001);aa.add(1002);List<Integer> bb = new ArrayList<>();bb.add(1001);bb.add(1002);Set<Integer> cc = new HashSet<>();Set<Integer> dd = new HashSet<>();dd.add(1);dd.add(2);System.out.println( CollectionUtils.containsAny(aa,bb));//trueSystem.out.println( CollectionUtils.containsAny(cc,dd));//false}
3.retainAll(Collection<?> c)
3.1、方法在java.util 包中 。
3.2、根据返回的集合数判断；大于0时存在交集。
boolean retainAll(Collection<?> c);
3.3、代码块
public boolean retainAll(Collection<?> c) {Objects.requireNonNull(c);return batchRemove(c, true);}private boolean batchRemove(Collection<?> c, boolean complement) {final Object[] elementData = this.elementData;int r = 0, w = 0;boolean modified = false;try {for (; r < size; r++)if (c.contains(elementData[r]) == complement)elementData[w++] = elementData[r];} finally {// Preserve behavioral compatibility with AbstractCollection,// even if c.contains() throws.if (r != size) {System.arraycopy(elementData, r,elementData, w,size - r);w += size - r;}if (w != size) {// clear to let GC do its workfor (int i = w; i < size; i++)elementData[i] = null;modCount += size - w;size = w;modified = true;}}return modified;}
public boolean retainAll(Collection<?> c) {Objects.requireNonNull(c);boolean modified = false;Iterator<E> it = iterator();while (it.hasNext()) {if (!c.contains(it.next())) {it.remove();modified = true;}}return modified;}
3.4、用法
public static void main(String[] args) {List<Integer> aa = new ArrayList<>();aa.add(1001);aa.add(1002);List<Integer> bb = new ArrayList<>();bb.add(1001);bb.add(1002);Set<Integer> cc = new HashSet<>();Set<Integer> dd = new HashSet<>();dd.add(1);dd.add(2);List<Integer> origin = new ArrayList<>();origin.addAll(aa);origin.retainAll(bb);System.out.println( origin.size() > 0 ? true : false);//trueSet<Integer> origin1 = new HashSet<>();origin1.addAll(cc);origin1.retainAll(dd);System.out.println( origin1.size() > 0 ? true : false);//false}
二、jdk1.8以上
List<String> intersection = list1.stream().filter(item -> list2.contains(item)).collect(toList());
