Methods inside array and call later Java

Question

I have a big problem that I really don't know the solution to, I can't seem to figure it out after hours of looking and trying stuff around...

I want to have an array which has methods inside, and I want to call them later on with their respective index, the test code looks like this:

package methods;

public class Methods {
    public static void main(String[] args) {
        Methods[] methodsArray = {print_something(), something_else()};
        methodsArray[0];
    }

    public static void print_something() {
        System.out.println("Hiya!");
    }
    public static void something_else() {
        System.out.println("Something else!");
    }
}

You can't readily do this in Java. Functions are not first-class objects. You need to rewrite your code to use functors or function interfaces. — Kamil Jarosz
– Kamil Jarosz, Commented Oct 29, 2018 at 18:15
@MarkRotteveel, You can.... kind of. But I thought you still have to structure your code appropriately. Can you actually do this without resorting to an interface in Java 8? That's the only way I know how to do it: an interface with a single function and a lambda expression. — Kamil Jarosz
– Kamil Jarosz, Commented Oct 30, 2018 at 17:25
@KamilJarosz Yes you need an interface (but those already exist, eg Runnable), but you don't necessarily need a lambda expression: a method reference works as well. — Mark Rotteveel
– Mark Rotteveel, Commented Oct 30, 2018 at 18:57

Peter Lawrey · Accepted Answer · 2018-10-29 18:16:16Z

6

You can do

public class Methods {
    public static void main(String[] args) {
        Runnable[] methodsArray = {Methods::print_something, Methods::something_else};
        methodsArray[0].run();
    }

    public static void print_something() {
        System.out.println("Hiya!");
    }
    public static void something_else() {
        System.out.println("Something else!");
    }
}

Accessing an array, only ever accesses the array and you can't change it to call a function in Java. You can do this in Kotlin, Groovy and Scala with operator overloading on a custom class (but not an array)

answered Oct 29, 2018 at 18:16

Peter Lawrey

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1 Comment

ree Over a year ago

Works perfectly, I didn't know I could use this in Java, thank you so much!

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