即使映射已填充，Map.size也会返回0，Map.values()也会返回空迭代器

import java.util.concurrent.ConcurrentHashMap;

ConcurrentHashMap<String, String> map = new ConcurrentHashMap<>();
map.put("key1", "value1");
System.out.println(map.size()); // 应该输出1

Map<String, String> map = new HashMap<>();
map.put("key1", "value1");
System.out.println(map.size()); // 应该输出1

Map<String, String> map = new HashMap<>();
map.put("key1", "value1");
System.out.println("Size after put: " + map.size());

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

public class MapExample {
    public static void main(String[] args) {
        Map<String, String> map = new HashMap<>();
        map.put("key1", "value1");
        map.put("key2", "value2");

        System.out.println("Map size: " + map.size()); // 应该输出2
        System.out.println("Map values: ");
        for (String value : map.values()) {
            System.out.println(value);
        }
    }
}