只演示默认的自然排序。

package com.njwbhz.March.week1.part0303;

import java.util.HashMap;
import java.util.Map;
import java.util.TreeMap;

public class TestTreeMap1 {
    public static void main(String[] args) {
        Map<String , String> countries = new TreeMap<String , String>();

        countries.put("CN","伟大的祖国");
        countries.put("JP","小日本");
        countries.put("KR","棒子");
        countries.put("RS","战斗民族");

        countries.entrySet().forEach(entry -> System.out.println(entry.getKey() + "————" + entry.getValue()));
    }
}