Check if hash map key is present before retrieving value [duplicate]

Question

Given I am checking my hashmap as follows

String firstName = map.get(UserDetail.FIRST_NAME); String lastName = map.get(UserDetail.LAST_NAME); String age = map.get(UserDetail.AGE); double height = Double.parseDouble(map.get(UserDetail.HEIGHT) double weight = Double.parseDouble(map.get(UserDetail.WEIGHT) String email = map.get(UserDetail.EMAIL);

How would I check that the key actually exists in my hashmap before attempting to retrieve the value. At the moment I keep getting a NullPointerException regularly.

davidxxx · Accepted Answer · 2017-10-20 07:42:34Z

Before Java 8, you have to explicitly do the check :

String firstName = map.get(UserDetail.FIRST_NAME); // null guard if (firstName != null){ // invoke a method on firstName }

After Java 8, you could use the Map.getOrDefault() method.

For example :

String firstName = map.getOrDefault(UserDetail.FIRST_NAME, "");

Now, in some cases, having a default value is not suitable as you want to do the processing only if the value is contained in the map and that is also not null.

In this configuration, a better way to address it is using Optional combined with ifPresent() :

Optional<String> optional = Optional.of(map.get(UserDetail.FIRST_NAME)); optional.ifPresent((s)->myProcessing());

You could also inline Optional if it used once :

Optional.of(map.get(UserDetail.FIRST_NAME)) .ifPresent((s)->myProcessing());

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