How to check if hashmap contains the key before getting it in the shortest way?-CodePudding

Is there any shorter way to find if the key already exists before getting it?

    Map<String, Double> map = new HashMap<>();
    if (map.containsKey("2")) {
        fee.put("2", fee.get("2")   12.00);
    } else {
        fee.put("2", 12.00);
    }

I want to add up the value.

CodePudding user response：

The most concise way to do this is:

map.merge(key, 12.0, Double::sum);

As described in the Javadoc, this default implementation is equivalent to:

 V oldValue = map.get(key);
 V newValue = (oldValue == null) ? value :
              remappingFunction.apply(oldValue, value);
 if (newValue == null)
     map.remove(key);
 else
     map.put(key, newValue);

where remappingFunction is Double::sum in this case.

CodePudding user response：

You can refactor it to use getOrDefault method from Map as follows:

   Map<String, Double> fee = new HashMap<>();
   fee.put("2", fee.getOrDefault("2", 0.0)   12.00);

Another way of doing it could be using Optionals:

    Map<String, Double> fee = new HashMap<>();
    fee.put("2", Optional.ofNullable(fee.get("2")).orElse(0.0)   12.00);