从Java中的Map中获取值的范围

发布时间：2020-12-15 08:47:42 所属栏目：Java 来源：网络整理

导读：是否有可能获得与 Java Map中的一系列键匹配的值.假设我有, MapKey,Value //size 10,000Key - 9.0,9.1,9.5,4.2,4.3,6.1,6.6Value - 10,20,30,40,60,10 ArrayList alMatch = {1.0,4.0,6.0} 在这种情况下,对于值4.0,我想得到40(关键4.2)和20(关键4.3).所以我希

是否有可能获得与 Java Map中的一系列键匹配的值.假设我有,

Map<Key,Value> //size 10,000
Key   - 9.0,9.1,9.5,4.2,4.3,6.1,6.6
Value - 10,20,30,40,60,10  

ArrayList alMatch = {1.0,4.0,6.0}

在这种情况下,对于值4.0,我想得到40(关键4.2)和20(关键4.3).所以我希望将所有值映射到Map中的键5.0> = key> = 4.0.是否可以通过Map或类似的数据结构来实现.

地图的大小很大.或者是否有其他更好的方法以最小的复杂性实现相同的目标.

解决方法

您可以使用NavigableMap的实现(示例TreeMap).这种方法特别值得您关注：

/**
 * Returns a view of the portion of this map whose keys range from
 * {@code fromKey} to {@code toKey}.  If {@code fromKey} and
 * {@code toKey} are equal,the returned map is empty unless
 * {@code fromExclusive} and {@code toExclusive} are both true.  The
 * returned map is backed by this map,so changes in the returned map are
 * reflected in this map,and vice-versa.  The returned map supports all
 * optional map operations that this map supports.
 *
 * <p>The returned map will throw an {@code IllegalArgumentException}
 * on an attempt to insert a key outside of its range,or to construct a
 * submap either of whose endpoints lie outside its range.
 *
 * @param fromKey low endpoint of the keys in the returned map
 * @param fromInclusive {@code true} if the low endpoint
 *        is to be included in the returned view
 * @param toKey high endpoint of the keys in the returned map
 * @param toInclusive {@code true} if the high endpoint
 *        is to be included in the returned view
 * @return a view of the portion of this map whose keys range from
 *         {@code fromKey} to {@code toKey}
 * @throws ClassCastException if {@code fromKey} and {@code toKey}
 *         cannot be compared to one another using this map's comparator
 *         (or,if the map has no comparator,using natural ordering).
 *         Implementations may,but are not required to,throw this
 *         exception if {@code fromKey} or {@code toKey}
 *         cannot be compared to keys currently in the map.
 * @throws NullPointerException if {@code fromKey} or {@code toKey}
 *         is null and this map does not permit null keys
 * @throws IllegalArgumentException if {@code fromKey} is greater than
 *         {@code toKey}; or if this map itself has a restricted
 *         range,and {@code fromKey} or {@code toKey} lies
 *         outside the bounds of the range
 */
NavigableMap<K,V> subMap(K fromKey,boolean fromInclusive,K toKey,boolean toInclusive);

TreeMap的底层数据结构是红色和黑色树,所有复杂性都由NavigableMap接口抽象,因此使用起来非常简单.

（编辑：李大同）

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