Java TreeMap 获取最小值和最大值

Question

我有这样的 TreeMap。在城镇中进行一些输入后，如何获得城镇温度的最小值和最大值？我不会复制在 towns 中填写一些值的代码，因为它工作正常。

Map<String, Town> towns = new TreeMap<>();

Town.class是这样的。

public class Town {

private int temperature;
private int rainfall;
private int windPower;
private Downwind downwind;

public Town(int temperature, int rainfall, int windPower, Downwind downwind) {
    this.temperature = temperature;
    this.rainfall = rainfall;
    this.windPower = windPower;
    this.downwind = downwind;
}

public int getTemperature() {
    return temperature;
}

public void setTemperature(int temperature) {
    this.temperature = temperature;
}

public int getRainfall() {
    return rainfall;
}

public void setRainfall(int rainfall) {
    this.rainfall = rainfall;
}

public int getWindPower() {
    return windPower;
}

public void setWindPower(int windPower) {
    this.windPower = windPower;
}

public Downwind getDownwind() {
    return downwind;
}

public void setDownwind(Downwind downwind) {
    this.downwind = downwind;
}

Answer 1

最简单的:

Optional<Town> maybeMinTown = towns.values().stream()
.min(Comparator.comparing(Town::getTemperature));

Town minTown = maybeMinTown.get(); // throws NoSuchElementException when towns map is empty

max 相同- 您只需要使用max而不是min .

更新

要获得刚好温度，您可以 map Town到温度然后调用min/max :

final OptionalInt min = towns.values().stream()
.mapToInt(Town::getTemperature)
.min();

min.getAsInt(); // or you can call min.orElseGet(some_lowest_value)

OptionalInt int 相同什么Optional<Town>用于Town .