How to call a method with parameters from an optional object in java

Question

Let's consider the following class

class A{
    void met(int i){
       //do somthing
    }
}

and let's consider that we have an optional object of this class like:

Optional<A> a;

is it possible to call the method met on the object a without the need to check whether a refers to a full object or just empty (null). Something like:

a.map(A::met(5));

Unfortunately this code doesn't compile. How can this be done?

so as if this line of code a.map(A::met(5)); doesn't exist — Anas
– Anas, Commented Dec 17, 2014 at 10:00

Eran · Accepted Answer · 2014-12-17 10:09:04Z

12

There are two reasons why this can't work:

a.map(A::met(5));

met returns nothing, and map must map the input Optional to an output Optional.
method references don't take arguments, so you should use a lambda expression.

What you need is :

a.ifPresent(x->x.met(5));

Another option :

a.orElse(new A()).met(5);

This will execute met(5) on a dummy instance if a is empty, so it's probably not the best way.

edited Dec 17, 2014 at 10:09

answered Dec 17, 2014 at 10:03

Eran

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2 Comments

Eran Over a year ago

@Anas It's just an arbitrary variable name whose type is A. It's a way to refer to the instance held by your Optional<A>

chrylis -cautiouslyoptimistic- Over a year ago

Depending on semantics, the latter option could work well with the Null Object pattern.

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