基于单个值使用不同的类

Question

I'm developing an application that should use different class types based on a single piece of information. To better illustrate my question, let me give an example:

suppose INFO is a boolean value. Based on its value, my code must use either instances of some class A , or some class B . Note that for every A , B is its subclass. INFO is set when the application starts and it's not changed throughout the app lifecycle.

My question: what's the most optimal way to implement this ?

Here are some approaches I've come up with, but feel free to suggest others:

1. Factory class with methods:

public static A getA(final boolean INFO) {
    return INFO ? new A() : new B();
}

2. Wrapper classes:

class WrapperForSomeClass {

    public final A instance;

    public WrapperForSomeClass(final boolean INFO) {
        instance = INFO ? new A() : new B();
    }

}

3. Interface + Factory class:

public interface IWrappable<T> {
    T get(final boolean INFO);
}

private static final IWrappable<A> WRAPPER_FOR_A = new IWrappable<A>() {
    public A get(final boolean INFO) {
        return INFO ? new A() : new B();
    }
};

public static A getA(final boolean INFO) {
    return WRAPPER_FOR_A.get(INFO);
}

If I had to choose, I'd go with no.3. What say ye?

Answer 1

I would do it as follows:

class A
{
}

class B extends A
{
}

class AFactory
{
    public A getInstance(boolean info) 
    {
        return info ? new A() : new B();
    }
}

class MyMainLauncher
{
    private AFactory aFactory;
    private A instance;

    {
        // has access to the boolean value `info`.
        instance = aFactory.getInstance(info);
    }
}

Answer 2

1 is shortest and cleanest. Place this method into A class, in order not to create redundant factory class.

Why you'd go for 3? It does the same, but with a lot more code.