Question

是否存在与c＃abstract KeyedCollection类具有相同行为的Java集合（即可以通过键和索引检索项目）？我环顾四周但找不到类似的东西。

谢谢，尼克

Answer 1

我认为您可以通过扩展HashMap来开发自己的类

Answer 2

我认为我能想到的最接近你想要的是树形图（http://docs.oracle.com/javase/7/docs/api/java/util/TreeMap.html），但是你不能只通过键来索引项目。

Answer 3

给出一个Entity类：

@Data // lombok.Data, to have getters and setters
public class Entity {
    private String myIndexingProperty;
    // Other fields here
}

尝试实现类似于C＃的KeyedCollection<T>的方法是（Java 8 +）：

import com.my.application.model.Entity;

import java.util.*;
import java.util.stream.Collectors;

public final class EntityMap implements Map<String, Entity> {
    private TreeSet<Entity> set;

    public EntityMap() {
        set = new TreeSet<>();
    }

    @Override
    public int size() {
        return set.size();
    }

    @Override
    public boolean isEmpty() {
        return set.isEmpty();
    }

    @Override
    public boolean containsKey(Object o) {
        return set.stream()
                .anyMatch(e -> String.valueOf(o).equalsIgnoreCase(e.getMyIndexingProperty()));
    }

    @Override
    public boolean containsValue(Object o) {
        return set.stream()
                .anyMatch(e -> String.valueOf(o).equalsIgnoreCase(e.getMyIndexingProperty()));
    }

    @Override
    public Entity get(Object o) {
        return set.stream()
                .filter(e -> String.valueOf(o).equalsIgnoreCase(e.getMyIndexingProperty()))
                .findFirst()
                .orElse(null);
    }

    @Override
    public Entity put(String s, Entity entity) {
        set.add(entity);
        return set.stream()
                .filter(e -> String.valueOf(entity.getMyIndexingProperty()).equalsIgnoreCase(e.getMyIndexingProperty()))
                .findFirst()
                .orElse(null);
    }

    @Override
    public Verb remove(Object o) {
        boolean removed = set.removeIf(e -> e.equals(o));
        if (!removed) {
            return null;
        }

        return get(o);
    }

    @Override
    public void putAll(Map<? extends String, ? extends Entity> map) {
        map.forEach(this::put);
    }

    @Override
    public void clear() {
        set.clear();
    }

    @Override
    public Set<String> keySet() {
        return set.stream()
                .map(Entity::getMyIndexingProperty)
                .collect(Collectors.toSet());
    }

    @Override
    public Collection<Entity> values() {
        return set;
    }

    @Override
    public Set<Entry<String, Entity>> entrySet() {
        return set.stream()
                .map(e -> new AbstractMap.SimpleEntry<>(e.getMyIndexingProperty(), e))
                .collect(Collectors.toSet());
    }
}

Java集合，如c＃KeyedColllection <tkey，titem>

3 个答案: