java键值对的数据结构

import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

public class ConcurrentHashMapExample {
    public static void main(String[] args) {
        Map<String, String> concurrentMap = new ConcurrentHashMap<>();
        concurrentMap.put("key1", "value1");
        concurrentMap.put("key2", "value2");
        System.out.println(concurrentMap.get("key1")); // 输出: value1
    }
}

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

public class NullCheckExample {
    public static void main(String[] args) {
        Map<String, String> map = new HashMap<>();
        String key = "key";
        String value = null;
        
        if (Objects.requireNonNull(key, "Key cannot be null") != null && 
            Objects.requireNonNull(value, "Value cannot be null") != null) {
            map.put(key, value);
        }
    }
}