import java.util.HashMap;

​

public class Main {

    public static void main(String[] args) {

        // 创建一个 HashMap

        HashMap<String, String> countries = new HashMap<>();

​

        // 往HashMap插入映射项

        countries.put("Washington", "America");

        countries.put("Canberra", "Australia");

        countries.put("Madrid", "Spain");

        System.out.println("HashMap: " + countries);

​

        //合并 key为 Washington的映射

        String returnedValue = countries.merge("Washington", "USA", (oldValue, newValue) -> oldValue + "/" + newValue);

        System.out.println("Washington: " + returnedValue);

​

        //输出更新后的HashMap

        System.out.println("Updated HashMap: " + countries);

    }

}