Java 8, Static methods vs Functions

Question

In Java 8 I want to create something that returns an argument or creates an instance if the argument is null.

I could do this by creating a static method or a UnaryOperator. Are the following approaches technically the same or are there technical differences that I should be aware of with either approach:

Static Method

static Cat initOrReturn(Cat c) {
    if (c==null) {
        return new Cat();
    }
    return c;
}

Function

UnaryOperator<Cat> initOrReturn = c -> {
    if (c==null) {
        return new Cat();
    }
    return c;
}

Re, "...could be used in ... streams." And would that help you to solve your problem? Or would it help some other software developer with whom you are working to solve a problem? You are asking developers for their opinions, but those opinions are going to depend on what problem you are trying to solve. — Solomon Slow
– Solomon Slow, Commented Dec 11, 2017 at 16:48
P.S., instead of "function," you might want to say "functional object." — Solomon Slow
– Solomon Slow, Commented Dec 11, 2017 at 16:50
Is c -> c==null? new Cat(): c really worth a discussion about different ways of reusability? — Holger
– Holger, Commented Dec 19, 2017 at 10:10
The question was really about the technical considerations of using a static method vs a function. — Andy Cribbens
– Andy Cribbens, Commented Dec 20, 2017 at 11:04

ice1000 · Accepted Answer · 2017-12-19 14:26:26Z

3

First your code has syntax error, in the second block first line between c and { there should be a ->.

The second one creates an anonynous object, the first one only creates a static method.
So they're not the same.

Also, static methods can be used in stream API.
If you have:

class A {
  static Object a(Object x) { return x; /* replace with your code */ }
}

You can:

xxxList().stream().map(A::a)

Creating a method is often considered dirty, because it's globally visible.
It's recommended to use lambda expressions without declaring a variable.

edited Dec 19, 2017 at 14:26

answered Dec 13, 2017 at 4:19

ice1000

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8 Comments

Andy Cribbens Over a year ago

So it sounds like the only technical consideration when deciding which approach to take, is that the Function creates an additional object. If this is a concern, then go with the static method? Otherwise, they both are easy to read, achieve the objective and can be used in streams.

ice1000 Over a year ago

Creating a method is often considered dirty, because it's global visible.

Andy Cribbens Over a year ago

Would you mind elaborating pls. Don't both approaches allow visibility restriction by the addition of visibility modifiers e.g. private etc?

ice1000 Over a year ago

Even it's private, it's accessible to the whole class. While a lambda expression can be a local variable, you can restrict its scope inside a method, or a for/while/if/else/dowhile block.

Andy Cribbens Over a year ago

That's really helpful. Thank you.

|

Emtec165 · Accepted Answer · 2022-05-23 23:32:07Z

You can think about function as a "value" - something that can be stored to variable, and passed around.

This "value" can be used as e.g. method parameter to (during runtime) dynamically change part of method implementation.

Take a look at this basic example. Hope that can illustrate idea:

static Number functionsUsageExample(Integer someValue, UnaryOperator<Number> unaryOperator) {
    if (someValue == 1) {
        //do something
    }
    Number result = unaryOperator.apply(someValue); // dynamically apply supplied implementation
    // do something else
    return result;
}

public static void main(String[] args) {
    UnaryOperator<Number> add = i -> i.doubleValue() + 20;
    UnaryOperator<Number> multiply = i -> i.intValue() * 3;

    var additionResult = functionsUsageExample(1, add);
    var multiplicationResult = functionsUsageExample(1, multiply);
    
    //additionResult value is:           21.0
    //multiplicationResult value is:     3
}

Function can be also used as a 'helper methods' stored inside method block. This way you will not corrupt class scope with method that is used only in one place.

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