import java.util.ArrayList;

import java.util.Collections;

import java.util.Comparator;

import java.util.HashMap;

import java.util.Iterator;

import java.util.List;

import java.util.Map;

import java.util.Map.Entry;

import java.util.Set;

public class Test {

    public static void main(String[] args) {

        Map<String, Integer> m = new HashMap<String, Integer>();

        m.put("a", 1);

        m.put("b", 1);

        m.put("c", 2);

        m.put("d", 3);

        System.out.println(getFristEntryOfSortedMap(m, true));

        System.out.println(getFristEntryOfSortedMap(m, false));

    }

    /**

     * 通过map 的 value 排序，并返回排序后的第一个条目

     *

     * @param m

     *            待排序集合

     * @param desc

     *            true:降序排序,false:升序排序

     * @return 返回排序后的第一个条目

     */

    public static Entry<String, Integer> getFristEntryOfSortedMap(Map<String, Integer> m, boolean desc) {

        if (m == null || m.isEmpty()) {

            throw new IllegalArgumentException("map is null or empty");

        }

        Set<Entry<String, Integer>> entrySet = m.entrySet();

        Iterator<Entry<String, Integer>> iterator = entrySet.iterator();

        while (iterator.hasNext()) {

            if (iterator.next().getValue() == null) {

                throw new IllegalArgumentException("map contains null value");

            }

        }

        List<Entry<String, Integer>> entryList = new ArrayList<Entry<String, Integer>>(entrySet);

        if (desc) {

            Collections.sort(entryList, new Comparator<Entry<String, Integer>>() {

                @Override

                public int compare(Entry<String, Integer> e1, Entry<String, Integer> e2) {

                    return e2.getValue() - e1.getValue();

                }

            });

        } else {

            Collections.sort(entryList, new Comparator<Entry<String, Integer>>() {

                @Override

                public int compare(Entry<String, Integer> e1, Entry<String, Integer> e2) {

                    return e1.getValue() - e2.getValue();

                }

            });

        }

        return entryList.get(0);

    }

}

d=3

a=1

import java.util.ArrayList;

import java.util.Collections;

import java.util.Comparator;

import java.util.List;

public class Test {

    public static void main(String[] args) {

        List<Person> list = new ArrayList<Person>();

        list.add(new Person(3, "d"));

        list.add(new Person(1, "a"));

        list.add(new Person(1, "b"));

        list.add(new Person(2, "c"));

        Collections.sort(list, new Comparator<Person>() {

            @Override

            public int compare(Person p1, Person p2) {

                return p2.getAge() - p1.getAge();

            }

        });

        System.out.println(list);

    }

}

class Person {

    private int age;

    private String name;

    Person(int age, String name) {

        this.age = age;

        this.name = name;

    }

    public int getAge() {

        return age;

    }

    public void setAge(int age) {

        this.age = age;

    }

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

    @Override

    public String toString() {

        return "Person [age=" + age + ", name=" + name + "]";

    }

}

[Person [age=3, name=d], Person [age=2, name=c], Person [age=1, name=a], Person [age=1, name=b]]