public static boolean containsKey(Map<String, String> map, String key) {
    for (Map.Entry<String, String> entry : map.entrySet()) {
        String keyValue = entry.getValue();
        if (key.equals(keyValue)) {
            return true;
        }
    }
    return false;
}

public static boolean containsKey(Map<String, String> map, String key) {
    return map.containsKey(key);
}

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

public class Main {
    public static void main(String[] args) {
        Map<String, String> map = new HashMap<String, String>() {{
            put("key1", "value1");
            put("key2", "value2");
            put("key3", "value3");
        }};

        System.out.println(containsKey(map, "key2")); // 输出：true
        System.out.println(containsKey(map, "key4")); // 输出：false
    }
}