如果你的值是唯一的，你可以使用 TreeMap，实现 NavigableMap，它有很好的 ceilingKey 和 floorKey 方法:

If your values are unique, you can use a TreeMap, which implements NavigableMap, which has the nice ceilingKey and floorKey methods:

    NavigableMap<Double, String> map = new TreeMap<>();
    map.put(0d, "A");
    map.put(0.25, "B");
    map.put(0.5, "C");
    map.put(0.75, "D");
    map.put(1d, "E");

    double value = 0.42;
    double above = map.ceilingKey(value);
    double below = map.floorKey(value);

    System.out.println(value - below > above - value ? above : below); //prints 0.5

注意:如果 value 小于(或大于)最小/最大键，则两种方法都可以返回 null.

Note: both methods can return null if value is less (resp. greater) than the smallest / largest key.