Question

我正在尝试填写一个像这样声明的地图

Map<Person, ArrayList<Location>> personByLocation = 
            new HashMap<String, ArrayList<Location>>();

这些是Person和Location：

public class Person {
    private Location location;
    private String name;

    public Person(Location location, String name) {
        this.location = location;
        this.name = name;
    }

    public Location getLocation() {
        return location;
    }

    public void setLocation(Location location) {
        this.location = location;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

public class Location {

    private LocationType locType;

    private String locWeather;

    public Location(LocationType locType, String locWeather) {
        this.locType = locType;
        this.locWeather = locWeather;
    }

    public LocationType getLocType() {
        return locType;
    }

    public void setLocType(LocationType locType) {
        this.locType = locType;
    }

    public String getLocWeather() {
        return locWeather;
    }

    public void setLocWeather(String locWeather) {
        this.locWeather = locWeather;
    }

    public enum LocationType {

        Amsterdam, London, Wiena, Paris, Egypt;
    }
}

我想在这张地图上做一个记录，但现在不知道怎么做。如果我创建Person的一个实例并将其作为一个Key放入一个记录作为该键值的数据将与ArrayList中的Location数据重复。

这是我做的，但它根本没用。

    Location location = new Location(LocationType.Paris, "sunny");
    Person person = new Person(new Location(LocationType.Paris, "sunny"), "Timm");

    for (Entry<Person, ArrayList<Location>> entry : personByLocation.entrySet()) {
        System.out.println(entry.getKey() + " " + entry.getValue());
    }

Answer 1

所有的拳头......这不会编译：

Map<Person, ArrayList<Location>> personByLocation = new HashMap<String, ArrayList<Location>>();

应将地图声明为：

Map<Person, ArrayList<Location>> personByLocation = new HashMap<Person, ArrayList<Location>>();

注意：我认为重点是，Person.location是Location的实际Person，而List<Locations>将是路线a人会做的。

创建位置和人员列表：

Location l1 = new Location(LocationType.Paris, "sunny");
Location l2 = new Location(LocationType.London, "cloudy");
Location l3 = new Location(LocationType.Wiena, "rain");

List<Location> list = new ArrayList<Location>();
list.add(l1);
list.add(l2);
list.add(l3);

Person person = new Person(new Location(LocationType.Paris, "sunny"), "Timm");

然后填写Map：

personByLocation.put(person, list);

如果你添加了另一个Person，那么它就不会被替换，而不是这个，如果你实际上在列表中的人，但更新了Person.location和{{1它将被替换。

注意：还考虑替换List<Location>实体的equals()和hashCode()方法。

Answer 2

我不建议按照@Mena建议将一个人的所有位置放入班级Person，只需从所有人那里取回Set<Location>。这是因为seperation of concerns。

首先，您需要修复地图的实例化。

Map<Person, List<Location>> personByLocation = new HashMap<Person, List<Location>>();

其次，地图检索到的值是List类型，为了打印每个元素，您实际上必须再次迭代它。

Location location = new Location(LocationType.Paris, "sunny");
Person person = new Person(location, "Timm");

for (Map.Entry<Person, List<Location>> entry : personByLocation.entrySet()) {
    Person p = entry.getKey();
    List<Location> locations = entry.getValue();
    for(Location loc : locations) {
        System.out.println(p + " " + loc);
    }
}

向地图添加值时，首先必须检查该人员是否已存在。否则，您将覆盖已为该人员存储的值。

List<Location> myLocations = new ArrayList<Location>();
...
if(personByLocation.containsKey(person)) {
    List<Location> storedLocations = personByLocation.get(person);
    storedLocations.addAll(myLocations);
} else {
    personByLocation.put(person, myLocations);
}

如何用这个参数制作一个java地图Map <object，arraylist <object =“”>＆gt;？

2 个答案: