concurrency - Inconsistent HashMap between classes - Java -


I have a square, which has a hashmap as a public field: 

  Public stable final hashmap < String, string & gt; Map = new hashmap & lt; String, string & gt; ();   
 And in class B (which is multi-threaded, applying runnabble), I put something.  
 Now, from class I want to read the map. But the changes in the map are class C. Are not reflected in.  
 I do not store any reference anywhere, but I use the map through the name of the class.  
  A map.put ("Hello", "hello"); // Thread B. A.map.get ("hi"); // in Thread C   
 and I'm sure that I get calls after calling () ..  
 I thought there could be a problem with concurrency And I have changed the Hashmap to Hashbabel, but it is still the same ..  
 I repeated this problem as short code as possible  
  Public Sector A {Public Static Last Hashmap & lt; String, string & gt; Map = new hashmap & lt; String, string & gt; (); Public static zero main (string [] args) {while (true); }} Public square b {public static zero main (string [] args) {scanner sc = new scanner (System.in); While (true) {string s = sc.nextLine (); A.map.put (s, "true"); Println (A.map.size ()); }}} Public class C {public static zero main (string [] args) {scanner sc = new scanner (System.in); While (true) {sc.nextLine (); Println (A.map.size ()); }}}   
 I can see the growing size in print in class B, but C is always zero in size  
 Am I missing something here ?   
 
 
 When you work with different threads, you  synchronize  to  
 Currently, you are not doing any synchronization, so it does not work.  
 So you have two options:  
     
  1.  
     In a synchronized map, wrap it with the  archive. Synchronize map (new hashmap . This applies synchronization to  all  operations, even if they come in the form of similar threads.   
  2.  
     Use the same lock while taking action on the map. I do not advise the latter method unless you are doing a lot of operations on one thread in succession, the other thread is not needed to know about it.    < According to the suggestion of p> and @ zikar, the use of the third option is to use  concurrent hashmap , code> archive. The synchronized map  does not come at the same price, which means that it should be your preferred option.

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