关于java concurrenthashmap替换方法的问题(Question about java concurrenthashmap replace method)

 我有以下代码 
 
public class Test{

private static final String key = "key";

public static void main(String[] a){
    ConcurrentHashMap<String,String > map = new ConcurrentHashMap<String,String>();
    System.out.println(map.replace(key,"1"));
    System.out.println(map.replace(key,"2"));
}

}
 
 输出两次都为null。 它不应该是1秒钟吗？ 

I have the following code
 
public class Test{

private static final String key = "key";

public static void main(String[] a){
    ConcurrentHashMap<String,String > map = new ConcurrentHashMap<String,String>();
    System.out.println(map.replace(key,"1"));
    System.out.println(map.replace(key,"2"));
}

}
 
The output is null both times. Isn't it supposed to be 1 second time?

原文：https://stackoverflow.com/questions/4949615