Question

Could a race codition occur when invoking method addId from multiple threads ?

private static Map<String , Long> table;

static {
    table = new ConcurrentHashMap<String  , Long>();
}

public static void addId(String key, Long value){

    if(table.containsKey(key)){
        table.remove(key);
    }

    table.put(key, value);
}

Answer 1

Nothing prevents another thread from putting some value between the containsKey/remove and the put, so checking if the table already contains a key before putting isn’t really “safe” (or rather, doesn’t really “make sense”).

Why don’t you just do

public static void addId(String key, Long value){
    table.put(key, value);
}

put will override any previous entry anyway.

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If you don’t want multiple threads to execute the method concurrently, declare the method as synchronized.