Java - Passing a class as a parameter

Question

I have a method that needs to create an array of objects of a certain type. Here's a part of it:

public void myMethod() {
    for (int i = 0; i < something.length; i++) {
        ViewerSorter sorter = new IdeaTableSorter(i);
        .....
        .....
    }
}

I want this method to work with all kinds of ViewerSorter objects, not just be coupled with IdeaTableSorter , but since I have to create a bunch of these objects I want to pass a reference to myMethod telling it which class to instantiate.

Is there a way to do this without using the Reflection API?

Answer 1

You can pass a Factory object that instantiates your class. This would be the Abstract factory pattern . For example:

interface ViewSorterFactory {
   ViewSorter create();
}
class IdeaTableSorterFactory implements ViewSorterFactory {
   ViewSorter create() { return new IdeaTableSorter(); }
}
class FooTableSorterFactory implements ViewSorterFactory {
   ViewSorter create() { return new FooSorter(); }
}

And then:

myMethod(new IdeaTableSorterFactory());

where:

for (int i = 0; i < something.length; i++) {
    ViewerSorter sorter = factory.create();

Class.newInstance() is not exactly the reflection API, though I assume you meant this option as undesirable. But give it a try - this approach is the same - you pass a factory (in this case Class ) and call a creation method ( .newInstance() )

Answer 2

Yes, you can do this using reflection. However, it would arguably be cleaner to use the Factory pattern:

public interface IViewerSorterFactory {
    ViewerSorter create(int i);
}

public void myMethod(IViewerSorterFactory factory) {
    for (int i = 0; i < something.length; i++) {
        ViewerSorter sorter = factory.create(i);
        .....
        .....
    }
}

Answer 3

You could pass in an object with a method that creates viewer sorters—a provider of sorts.

public void myMethod(ViewerSorterProvider creator) {
    for (int i = 0; i < something.length; i++) {
        ViewerSorter sorter = creator.create(i);
        .....
        .....
    }
}

public interface ViewerSorterProvider {
    ViewerSorter create(int i);
}

Answer 4

You could pass a factory object into the method that can create the appropriate types.