Seeking elegant way to combine varying types with case-switch

[Eric Barnhill]

I want to design a library that takes as input arrays of varying dimension and variable type, then processes them in different pipelines according to a preferences file. The idea is that the switch method will choose one of these pipelines, and an overload will handle the varying types.

I have written some toy code that abstracts the problem. I think if I could get this code to work I would know how to design my project.

I have a base class Foo which takes an argument of either Float or Double type, and an integer for preferred pipeline. Here is the code I have written for this. Note it does not compile.

package genericsSandbox2;

public class Foo<T> {

    T t;
    int preferredBar;

    public Foo(T t, int preferredBar) {
        this.preferredBar = preferredBar;
        this.t = t;
        callBar();
    }

    void callBar() {
        switch(preferredBar) {
            case 1:
                Bar1 bar1 = new Bar1(t);
                break;
            case 2:
                Bar2 bar1 = new Bar2(t);
                break;
        }
    }

    public static void main(String[] args) {
        Double zerodouble = 0.0;
        Float zerofloat = 0.0f;
        Foo<Double> f1double = new Foo<Double>(zerodouble, 1);
        Foo<Float> f1float= new Foo<Float>(zerofloat, 1);
        Foo<Double> f2double = new Foo<Double>(zerodouble, 2);
        Foo<Float> f2float = new Foo<Float>(zerofloat, 2);
    } 
        
}

I then have two pipeline classes Bar1 and Bar2 . These both compile.

package genericsSandbox2;

public class Bar1 {
    
    public void Bar1(Float f) {
        System.out.println("Bar 1 float");
    }
    
    public void Bar1(Double f) {
        System.out.println("Bar 1 double");
    }

}

and

package genericsSandbox2;

public class Bar2 {
    
    public void Bar2(Float f) {
        System.out.println("Bar 2 float");
    }
    
    public void Bar2(Double f) {
        System.out.println("Bar 2 double");
    }

}

The desired output is

Bar 1 Double
Bar 1 Float
Bar 2 Double
Bar 2 Float

However the compiler isn't having any

Foo.java:17: error: no suitable constructor found for Bar1(T)                Bar1 bar1 = new Bar1(t);                            ^    constructor Bar1.Bar1(Float) is not applicable      (argument mismatch; T cannot be converted to Float)    constructor Bar1.Bar1(Double) is not applicable      (argument mismatch; T cannot be converted to Double)  where T is a type-variable:    T extends Object declared in class Foo Foo.java:20: error: no suitable constructor found for Bar2(T)                Bar2 bar2 = new Bar2(t);                            ^    constructor Bar2.Bar2(Float) is not applicable      (argument mismatch; T cannot be converted to Float)    constructor Bar2.Bar2(Double) is not applicable      (argument mismatch; T cannot be converted to Double)  where T is a type-variable:    T extends Object declared in class Foo 2 errors

I would really like to do this some more elegant way than casting the Object. Am I stuck casting the Object or is there a more elegant way to handle these cases?

[Campbell Ritchie]

I can't understand most of that code, I am afraid.
If you want to instantiate different types depending on circumstances, consider

1: Giving those types a common maybe abstract supertype.

2: Don't try to distinguish methods by their parameter types like that.

3: Give the supertype static factory methods which can instantiate subtypes if required. It might be neater to have the subtypes as private nested classes.

4: Consider passing some parameter whose value (not type) hints at the subtype required, e.g. a String or an enum element.

I do not believe you can pass such arrays to a switch statement because the cases have to be of type enum XYZ or int or String.

[Eric Barnhill]

Unfortunately the Bar methods are somehow not right. The void keyword should not be there and those are constructors not methods. When they are constructors you get the compiler message seen there. I must have posted the wrong vim register but don't see a way to edit my post.

But, I think your answers would still be the same. It looks like the most elegant solution is probably to take an Object argument and then using getClass() cast it and pass it on to the relevant subtype and method. Thanks!