在标准Java库中，找出两个list是否包含完全相同的元素的最简单方法是什么?
这两个list是否为相同实例并不重要，这两个list的类型参数是否不同也不重要。
e.g.
List list1
List<String> list2;
// ... construct etc
list1.add("A");
list2.add("A");
// the function, given these two lists, should return true
我知道可能有什么东西在盯着我的脸:-)
编辑:为了澄清，我正在寻找完全相同的元素和元素的数量，按顺序。
当前回答
我的解决方案适用于不关心列表中的顺序的情况——换句话说:具有相同元素但顺序不同的列表将被认为具有相同的内容。
示例:["word1"， "word2"]和["word2"， "word1"]被认为内容相同。
我已经谈到了订购，我还需要说一些关于副本的事情。列表需要具有相同数量的元素才能被认为是相等的。
例如:["word1"]和["word1"， "word1"]被认为不具有相同的内容。
我的解决方案:
public class ListUtil {
public static <T> boolean hasSameContents(List<T> firstList, List<T> secondList) {
if (firstList == secondList) { // same object
return true;
}
if (firstList != null && secondList != null) {
if (firstList.isEmpty() && secondList.isEmpty()) {
return true;
}
if (firstList.size() != secondList.size()) {
return false;
}
List<T> tmpSecondList = new ArrayList<>(secondList);
Object currFirstObject = null;
for (int i=1 ; i<=firstList.size() ; i++) {
currFirstObject = firstList.get(i-1);
boolean removed = tmpSecondList.remove(currFirstObject);
if (!removed) {
return false;
}
if (i != firstList.size()) { // Not the last element
if (tmpSecondList.isEmpty()) {
return false;
}
}
}
if (tmpSecondList.isEmpty()) {
return true;
}
}
return false;
}
}
我用Strings进行了测试，如下所示:
@Test public void testHasSameContents() throws Exception { // comparing with same list => no duplicate elements Assert.isTrue(ListUtil.hasSameContents(List.of("one", "two", "three"), List.of("one", "two", "three"))); // comparing with same list => duplicate elements Assert.isTrue(ListUtil.hasSameContents(List.of("one", "two", "three", "one"), List.of("one", "two", "three", "one"))); // compare with disordered list => no duplicate elements Assert.isTrue(ListUtil.hasSameContents(List.of("one", "two", "three"), List.of("three", "two", "one"))); // compare with disordered list => duplicate elements Assert.isTrue(ListUtil.hasSameContents(List.of("one", "two", "three", "one"), List.of("three", "two", "one", "one"))); // comparing with different list => same size, no duplicate elements Assert.isFalse(ListUtil.hasSameContents(List.of("one", "two", "three"), List.of("four", "five", "six"))); // comparing with different list => same size, duplicate elements Assert.isFalse(ListUtil.hasSameContents(List.of("one", "two", "two"), List.of("one", "two", "three"))); Assert.isFalse(ListUtil.hasSameContents(List.of("one", "two", "three"), List.of("one", "two", "two"))); // comparing with different list => different size, no duplicate elements Assert.isFalse(ListUtil.hasSameContents(List.of("one", "two", "three", "four"), List.of("one", "two", "three"))); Assert.isFalse(ListUtil.hasSameContents(List.of("one", "two", "three"), List.of("one", "two", "three", "four"))); // comparing with different list => different sizes, duplicate elements Assert.isFalse(ListUtil.hasSameContents(List.of("one", "two", "three", "one"), List.of("one", "two", "three"))); Assert.isFalse(ListUtil.hasSameContents(List.of("one", "two", "three"), List.of("one", "two", "three", "one"))); }
其他回答
我的解决方案适用于不关心列表中的顺序的情况——换句话说:具有相同元素但顺序不同的列表将被认为具有相同的内容。
示例:["word1"， "word2"]和["word2"， "word1"]被认为内容相同。
我已经谈到了订购，我还需要说一些关于副本的事情。列表需要具有相同数量的元素才能被认为是相等的。
例如:["word1"]和["word1"， "word1"]被认为不具有相同的内容。
我的解决方案:
public class ListUtil {
public static <T> boolean hasSameContents(List<T> firstList, List<T> secondList) {
if (firstList == secondList) { // same object
return true;
}
if (firstList != null && secondList != null) {
if (firstList.isEmpty() && secondList.isEmpty()) {
return true;
}
if (firstList.size() != secondList.size()) {
return false;
}
List<T> tmpSecondList = new ArrayList<>(secondList);
Object currFirstObject = null;
for (int i=1 ; i<=firstList.size() ; i++) {
currFirstObject = firstList.get(i-1);
boolean removed = tmpSecondList.remove(currFirstObject);
if (!removed) {
return false;
}
if (i != firstList.size()) { // Not the last element
if (tmpSecondList.isEmpty()) {
return false;
}
}
}
if (tmpSecondList.isEmpty()) {
return true;
}
}
return false;
}
}
我用Strings进行了测试，如下所示:
@Test public void testHasSameContents() throws Exception { // comparing with same list => no duplicate elements Assert.isTrue(ListUtil.hasSameContents(List.of("one", "two", "three"), List.of("one", "two", "three"))); // comparing with same list => duplicate elements Assert.isTrue(ListUtil.hasSameContents(List.of("one", "two", "three", "one"), List.of("one", "two", "three", "one"))); // compare with disordered list => no duplicate elements Assert.isTrue(ListUtil.hasSameContents(List.of("one", "two", "three"), List.of("three", "two", "one"))); // compare with disordered list => duplicate elements Assert.isTrue(ListUtil.hasSameContents(List.of("one", "two", "three", "one"), List.of("three", "two", "one", "one"))); // comparing with different list => same size, no duplicate elements Assert.isFalse(ListUtil.hasSameContents(List.of("one", "two", "three"), List.of("four", "five", "six"))); // comparing with different list => same size, duplicate elements Assert.isFalse(ListUtil.hasSameContents(List.of("one", "two", "two"), List.of("one", "two", "three"))); Assert.isFalse(ListUtil.hasSameContents(List.of("one", "two", "three"), List.of("one", "two", "two"))); // comparing with different list => different size, no duplicate elements Assert.isFalse(ListUtil.hasSameContents(List.of("one", "two", "three", "four"), List.of("one", "two", "three"))); Assert.isFalse(ListUtil.hasSameContents(List.of("one", "two", "three"), List.of("one", "two", "three", "four"))); // comparing with different list => different sizes, duplicate elements Assert.isFalse(ListUtil.hasSameContents(List.of("one", "two", "three", "one"), List.of("one", "two", "three"))); Assert.isFalse(ListUtil.hasSameContents(List.of("one", "two", "three"), List.of("one", "two", "three", "one"))); }
private boolean listHaveEqualObjects(List<?> list1, List<?> list2){
return list1.containsAll(list2) && list2.containsAll(list1);
很晚才加入这个派对，但想添加这个空安全检查:
Objects.equals(list1, list2)
如果您正在使用(或乐于使用)Apache Commons Collections，您可以使用CollectionUtils。isEqualCollection“如果给定集合包含完全相同的元素和完全相同的基数，则返回true。”
当两个列表具有相同的元素，但顺序不同时的解决方案:
public boolean isDifferentLists(List<Integer> listOne, List<Integer> listTwo) {
if(isNullLists(listOne, listTwo)) {
return false;
}
if (hasDifferentSize(listOne, listTwo)) {
return true;
}
List<Integer> listOneCopy = Lists.newArrayList(listOne);
List<Integer> listTwoCopy = Lists.newArrayList(listTwo);
listOneCopy.removeAll(listTwoCopy);
return CollectionUtils.isNotEmpty(listOneCopy);
}
private boolean isNullLists(List<Integer> listOne, List<Integer> listTwo) {
return listOne == null && listTwo == null;
}
private boolean hasDifferentSize(List<Integer> listOne, List<Integer> listTwo) {
return (listOne == null && listTwo != null) || (listOne != null && listTwo == null) || (listOne.size() != listTwo.size());
}
