Changing the type of primitive arrays in Java

问题

I have a numeric program in Java that does a lot of operations on primitive arrays. I use primitive arrays (double[]/float[]/int[]) because they are much more memory and time-efficient than dealing with arrays of pointers to values (e.g. ArrayList<Float>).

Now, I want to be able to change my primitive type, eg. from double to float, based on some parameter to my program. But since primitive can not be used as generics, I can't for the life of me figure out how.

Is there any way, or is the vast amount of code replication or casting I have to do just an unavoidable flaw of Java?

回答1:

Do you really need to deal with primitive types only? If not, you could consider having an array of Number - this way you can instantiate either a Float[] or Double[].

Number numbers[] = (param == "float" ? new Float[n] : new Double[n]);

I assume using wrappers is less efficient than using primitives (I haven't benchmarked though) but it's sure faster than using Collections (eg ArrayList).

回答2:

Here's a possible implementation of a wrapper class:

public class NumberListWrapper<T extends Number> {
    private ArrayList<T> numbers = new ArrayList<>();

    public boolean add(T num) {
        return numbers.add(num);
    }

    public boolean contains(T num) {
        return numbers.contains(num);
    }

    public boolean remove(T num) {
        return numbers.remove(num);
    }

    public float[] toFloatArray() {
        float[] floats = new float[numbers.size()];

        for(int i = 0; i < numbers.size(); i++) {
            floats[i] = numbers.get(i).floatValue();
        }

        return floats;
    }
}

Other primitive array conversions use the same pattern as this float one.

Edit: You probably want a get() method too... lol

来源：https://stackoverflow.com/questions/35270381/changing-the-type-of-primitive-arrays-in-java