8

The Type class provides a way to dynamically instantiate a class based on a String name, so we can access member variables and instance methods. Is there a way to access static methods using this same mechanism?

What I'd like to do:

global interface Vehicle {
  Long getMaxSpeed();
  String getType();
  // added to sample, not possible
  static String getSomething();
}

global class VehicleImpl implements Vehicle {
  global Long getMaxSpeed() { return 100; }   
  global String getType() { return 'Sedan'; }
  // added to sample
  global static String getSomething() { return 'Something'; }
}

public class CustomerImplInvocationClass {
    public static void invokeCustomImpl() {
        // Get the class name from a custom setting.
        // This class implements the Vehicle interface.
        CustomImplementation__c cs = CustomImplementation__c.getInstance('Vehicle');

        // Get the Type corresponding to the class name
        Type t = Type.forName(cs.className__c);

        // Instantiate the type.
        // The type of the instantiated object 
        //   is the interface.
        Vehicle v = (Vehicle)t.newInstance();

        // Call the methods that have a custom implementation
        System.debug('Max speed: ' + v.getMaxSpeed());
        System.debug('Vehicle type: ' + v.getType());       
        // added
        System.debug('Something?: ' + t.getSomething());       
    }
}
6
7

Nope, at time of writing, the Type class can't do that.

The Type class can instantiate a class based on a string...and that's about it. Yes, there are a few other methods, but I've never come across a situation where I've actually used anything other than Type.forName() and Type.newInstance().

About the closest you'd be able to get is to have a public, non-static method in your target class (or any class, really) that calls your class's static method. I've personally used something close to this in the trigger framework I developed for my company (I retrieve a static class variable, rather than call a static method).

I can't quite put my finger on it, but having a public method that calls a class's static method feels like it defeats the purpose of having a static method.

4
  • 2
    The remaining methods are actually useless, although it does implement the methods that allows Type to be used in a Set (equals and hashCode), which you could theoretically use for caching ... something.
    – sfdcfox
    Aug 2 '16 at 19:44
  • Also, mention this idea. More votes is better!
    – sfdcfox
    Aug 2 '16 at 19:49
  • @sfdcfox That might be useful in a lazy factory...maybe. At that point though, it's probably better to just cache object instances by the string name that you'd already have.
    – Derek F
    Aug 2 '16 at 19:53
  • Accepted your answer. This is the approach I started a couple hours ago, was hoping for something better.
    – Ray Dehler
    Aug 2 '16 at 20:35
0

I was just researching this myself. I created a unlocked package without org dependency. Rather than pulling in all the classes just call a static method, I was trying to determine a way to call the static method using reflection of some sort.

So far the answer seems to be no, I simply cannot do that.

1
  • I'm in the same boat. The only way around this I can see to to avoid static method and public enums if you want to build a loosely coupled interface.
    – muchavie
    Aug 21 at 11:47
0

The OP was very close, there is a 'feature' in Apex that allows static methods to fulfil the contract of an interface, so this works, although it really really shouldn't.

public class Foo implements Bar {
    
    public interface Bar {
        void doSomething();
    }
    
    public static void doSomething() {
        System.debug('Hello');
    }
    
    public static void callIt() {
        Bar iBar = (Bar)Type.forName('Foo').newInstance();
        iBar.doSomething();
    }
}

Ref: ChuckJonas/wtfapex

2
  • I'm getting the error: Static method cannot be referenced from a non static context. Very close though.
    – muchavie
    Aug 7 at 23:04
  • @muchavie How did you test that, could be they have changed behaviour somewhere but the code as written is deploying and running for me without error. Aug 9 at 18:19

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