Using an object to instantiate a collection

I would like to do the following (which doesn't work, it is just to explain the concept). Any idea how to do it?

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Class type;
if (/* something */)
  type = String.class;
else
  type = Boolean.class;

return new ArrayList<type>();

ArrayList<type> doesn't work. I tried with type.getClass(), doesn't work either.

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Wrap it into the method, pass the type as generic Class and let Java do the rest for you. No need for any conditional branching.

<T> List<T> newList(Class<T> type) {
    return new ArrayList<T>();
}

Then you can use it like this:

List<String> list = newList(String.class);

Bear in mind that T does not have to be specified at the generic class level. You can specify generic type for the method and therefore make it a generic method as in the example code.

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You can't do that. Your check happens at runtime and generics are lost after compilation.

The only purpose of generics is to guarantee type-safety at compile-time. In your example you want to determine the type at runtime.

What you can do is to instantiate a differently-typed collection in each if.

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you should use:

public ArrayList<?> getList() {
    if (/* something */) {
        return new ArrayList<String>();
    } else {
        return new ArrayList<Boolean>();
    }
}

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Type information is deleted by the Java compiler but can be accessed through additional packages such as this one

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type isn't a class , You can have multiple return in this case You can have this

public <T> List<T> foo(T type) {
    return new ArrayList<T>();
}

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The if clause is presumably something that is decided at run-time. The parameterised types in java are cleared at compile time. Just returning new ArrayList() will have the same effect.