java - 查找键的最大值
问题描述
public class Task1 {
public static void main(String[] args) {
Map<String, List<String>> map = new HashMap<String, List<String>>();
List<String> valSetOne = new ArrayList<String>();
valSetOne.add("0.00");
valSetOne.add("0.01");
valSetOne.add("1.00");
List<String> valSetTwo = new ArrayList<String>();
valSetTwo.add("0.00");
valSetTwo.add("0.01");
List<String> valSetThree = new ArrayList<String>();
valSetThree.add("0.01");
valSetThree.add("1.00");
List<String> valSetFour = new ArrayList<String>();
valSetFour.add("0.01");
map.put("HR3-A1234", valSetOne);
map.put("HR3-A2345", valSetTwo);
map.put("HR3-A3456", valSetThree);
map.put("HR3-A4567", valSetFour);
for (Map.Entry<String, List<String>> entry : map.entrySet()) {
String key = entry.getKey();
List<String> values = entry.getValue();
Object obj = Collections.max(values);
System.out.println("Value of " + key + " is " + obj);
}
}
}
这是我的代码,它工作得很好。对于键 HR3-A2345,我想找到最小值,而对于其他记录,我需要最大值。有人可以建议我一个解决方案吗?
解决方案
如果您不想使用if...else
,那么我建议在将集合放入地图之前对集合进行排序以首先放置所需的元素。例如:
final BiFunction<List<String>, Comparator<String>, List<String>> sort = (values, comparator) -> {
values.sort(comparator);
return values;
};
Map<String, List<String>> map = new HashMap<>();
map.put("HR3-A1234", sort.apply(valSetOne(), null)); // first element is min
map.put("HR3-A2345", sort.apply(valSetTwo(), Collections.reverseOrder())); // first element is max
map.put("HR3-A3456", sort.apply(valSetThree(), null)); // first element is min
map.put("HR3-A4567", sort.apply(valSetFour(), null)); // first element is min
map.forEach((key, values) ->
System.out.println("Value of " + key + " is " + (values != null && !values.isEmpty() ? values.iterator().next() : null)));
笔记:
- 我可以看到,你想比较双值,但在你的例子中你比较
Strings
!这不一样。在这种情况下,您必须在代码中替换String
为Double
。 - 如果无法复制值,则
List
可以使用TreeSet
所需的比较器来代替使用。
例如;
public static void main(String... args) {
Map<String, Set<Double>> map = new HashMap<>();
map.put("HR3-A1234", valSetOne(null)); // first element is min
map.put("HR3-A2345", valSetTwo(Collections.reverseOrder())); // first element is max
map.put("HR3-A3456", valSetThree(null)); // first element is min
map.put("HR3-A4567", valSetFour(null)); // first element is min
map.forEach((key, values) -> {
if (values != null && !values.isEmpty())
System.out.format("Value of %s is %.2f\n", key, values.iterator().next());
});
}
private static Set<Double> valSetOne(Comparator<Double> comparator) {
Set<Double> values = new TreeSet<>(comparator);
values.add(.0);
values.add(.01);
values.add(1.);
return values;
}
private static Set<Double> valSetTwo(Comparator<Double> comparator) {
Set<Double> values = new TreeSet<>(comparator);
values.add(.0);
values.add(.01);
return values;
}
private static Set<Double> valSetThree(Comparator<Double> comparator) {
Set<Double> values = new TreeSet<>(comparator);
values.add(.01);
values.add(1.);
return values;
}
private static Set<Double> valSetFour(Comparator<Double> comparator) {
Set<Double> values = new TreeSet<>(comparator);
values.add(.01);
return values;
}