我想根据谓词筛选java.util.Collection。
当前回答
这里有一些非常棒的答案。对我来说,我想让事情尽可能简单易懂:
public abstract class AbstractFilter<T> {
/**
* Method that returns whether an item is to be included or not.
* @param item an item from the given collection.
* @return true if this item is to be included in the collection, false in case it has to be removed.
*/
protected abstract boolean excludeItem(T item);
public void filter(Collection<T> collection) {
if (CollectionUtils.isNotEmpty(collection)) {
Iterator<T> iterator = collection.iterator();
while (iterator.hasNext()) {
if (excludeItem(iterator.next())) {
iterator.remove();
}
}
}
}
}
其他回答
您可以使用ForEach DSL编写
import static ch.akuhn.util.query.Query.select;
import static ch.akuhn.util.query.Query.$result;
import ch.akuhn.util.query.Select;
Collection<String> collection = ...
for (Select<String> each : select(collection)) {
each.yield = each.value.length() > 3;
}
Collection<String> result = $result();
给定一个集合[The, quick, brown, fox, jumping, over, The, lazy, dog],结果是[quick, brown, jumping, over, lazy],即所有字符串都长于三个字符。
ForEach DSL支持的所有迭代样式都是
AllSatisfy AnySatisfy 收集 Counnt CutPieces 检测 GroupedBy IndexOf InjectInto 拒绝 选择
更多详情请参考https://www.iam.unibe.ch/scg/svn_repos/Sources/ForEach
这里有一些非常棒的答案。对我来说,我想让事情尽可能简单易懂:
public abstract class AbstractFilter<T> {
/**
* Method that returns whether an item is to be included or not.
* @param item an item from the given collection.
* @return true if this item is to be included in the collection, false in case it has to be removed.
*/
protected abstract boolean excludeItem(T item);
public void filter(Collection<T> collection) {
if (CollectionUtils.isNotEmpty(collection)) {
Iterator<T> iterator = collection.iterator();
while (iterator.hasNext()) {
if (excludeItem(iterator.next())) {
iterator.remove();
}
}
}
}
}
我需要根据列表中已经存在的值来筛选列表。例如,删除后面小于当前值的所有值。{2 5 3 4 7 5} ->{2 5 7}。或者例如删除所有重复项{3 5 4 2 3 5 6}->{3 5 4 2 6}。
public class Filter {
public static <T> void List(List<T> list, Chooser<T> chooser) {
List<Integer> toBeRemoved = new ArrayList<>();
leftloop:
for (int right = 1; right < list.size(); ++right) {
for (int left = 0; left < right; ++left) {
if (toBeRemoved.contains(left)) {
continue;
}
Keep keep = chooser.choose(list.get(left), list.get(right));
switch (keep) {
case LEFT:
toBeRemoved.add(right);
continue leftloop;
case RIGHT:
toBeRemoved.add(left);
break;
case NONE:
toBeRemoved.add(left);
toBeRemoved.add(right);
continue leftloop;
}
}
}
Collections.sort(toBeRemoved, new Comparator<Integer>() {
@Override
public int compare(Integer o1, Integer o2) {
return o2 - o1;
}
});
for (int i : toBeRemoved) {
if (i >= 0 && i < list.size()) {
list.remove(i);
}
}
}
public static <T> void List(List<T> list, Keeper<T> keeper) {
Iterator<T> iterator = list.iterator();
while (iterator.hasNext()) {
if (!keeper.keep(iterator.next())) {
iterator.remove();
}
}
}
public interface Keeper<E> {
boolean keep(E obj);
}
public interface Chooser<E> {
Keep choose(E left, E right);
}
public enum Keep {
LEFT, RIGHT, BOTH, NONE;
}
}
这将被这样使用。
List<String> names = new ArrayList<>();
names.add("Anders");
names.add("Stefan");
names.add("Anders");
Filter.List(names, new Filter.Chooser<String>() {
@Override
public Filter.Keep choose(String left, String right) {
return left.equals(right) ? Filter.Keep.LEFT : Filter.Keep.BOTH;
}
});
考虑使用支持泛型的更新的Collections框架谷歌Collections。
更新:谷歌集合库现在已弃用。你应该使用最新发布的番石榴。它仍然具有对集合框架的所有相同扩展,包括基于谓词进行筛选的机制。
谷歌的Guava库中的Collections2.filter(Collection,Predicate)方法正是您所寻找的。
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