java 根据对象的成员变量从值对 HashMap 进行排序

Sort HashMap basis on Object's member variable from value

提问by Navnath

Have one class

上一节课

class Employee {
    int id;
    String name;
}

and one map which contains this object in value

以及一张包含该对象价值的地图

Map<Integer, Employee> map = new HashMap<Integer, Employee>();

Now I want to sort above mapone the basis of Employee's name. Means when I iterate this map using Map.Entry, Employeeobjects must retrive alphabetically.

现在，我要排序上面map一个基础Employee's name。意味着当我使用 迭代此地图时Map.Entry，Employee对象必须按字母顺序检索。

Thanks in advance

提前致谢

采纳答案by Navnath

Micha?l suggested one link which is Sort a Map<Key, Value> by values (Java). I did some change in it. and it works for me

Micha?l 建议了一个链接，它是Sort a Map<Key, Value> by values (Java)。我做了一些改变。它对我有用

class ValueComparator implements Comparator<Integer> {

    Map<Integer, Employee> base;
    public ValueComparator(Map<Integer, Employee> base) {
        this.base = base;
    }

    // Note: this comparator imposes orderings that are inconsistent with equals.    
    public int compare(Integer a, Integer b) {
        return ((Employee)base.get(a)).compareTo(base.get(b));
    }

}

class Employee implements Comparable {
    public String name;
    public int id;

    Employee(int id, String name) {
        this.id = id;
        this.name = name;
    }

    @Override
    public int compareTo(Object obj) {
        return this.name.compareTo(((Employee)obj).name);
    }

    public String toString() {
        return name;
    }
}

For solution please refere above mension link too.

有关解决方案，请参阅上面的链接。

Thanks for all who have reply.

感谢所有回复的人。

回答by anubhava

Use a TreeMapwith a custom Comparatorusing this constructor:

使用带有自定义Comparator的TreeMap使用此构造函数：

http://docs.oracle.com/javase/6/docs/api/java/util/TreeMap.html#TreeMap(java.util.Comparator)

http://docs.oracle.com/javase/6/docs/api/java/util/TreeMap.html#TreeMap(java.util.Comparator)

回答by dcernahoschi

You can't sort a HashMap, but you can sort its entries obtained with entrySet().

您不能对 进行排序HashMap，但可以对通过 获得的条目进行排序entrySet()。

public class MapSort {
    private static class Employee {
        public String name;

        public Employee(String name) {
            this.name = name;
        }

        @Override
        public String toString() {
           return name;
        }
    }

    public static void main(String[] args) {
        Map<Integer, Employee> map = new HashMap<Integer, Employee>();

        map.put(1, new MapSort.Employee("x"));
        map.put(2, new MapSort.Employee("a"));
        map.put(3, new MapSort.Employee("f"));

        List<Map.Entry<Integer, Employee>> entryList = new ArrayList<Map.Entry<Integer, Employee>>(map.entrySet());

            Collections.sort(
                    entryList, new Comparator<Map.Entry<Integer, Employee>>() {
                @Override
                public int compare(Map.Entry<Integer, Employee> integerEmployeeEntry,
                                   Map.Entry<Integer, Employee> integerEmployeeEntry2) {
                    return integerEmployeeEntry.getValue().name
                            .compareTo(integerEmployeeEntry2.getValue().name);
                }
            }
        );

        System.out.println(entryList);
    }
}

After sorting you can put back your entries in a map that supports ordering, for example LinkedHashMap.

排序后，您可以将条目放回支持排序的映射中，例如LinkedHashMap。

It depends on your use case: if you need to keep the map always sorted it's simpler to employ a TreeMapthat comes with an additional overhead. If you need just an one time sorting, you can use a HashMapwith the above code.

这取决于您的用例：如果您需要始终对地图进行排序，那么使用TreeMap带有额外开销的a会更简单。如果你只需要一次排序，你可以使用HashMap上面的代码。