How should I initialize an array of classes with a default (parameterless) constructor in Java?

Question

How should I initialize an array of classes with an empty constructor?

I can see that if I was using the constructor I would do it like so -

MyClass[] myArray = new MyClass[] {
    new MyClass(1),
    new MyClass(2),
    new MyClass(3)
};

But with an empty constructor I'm not sure what to do.

MyClass[] myArray = new MyClass[] {
    new MyClass(),
    new MyClass(),
    new MyClass()
};

This is what I have at the moment, but it seems terribly inefficient - is there a better way?

(I called it MyClass / myArray for readability in the example - don't worry, I do use sensible variable names!)

With only three members it's not really inefficient. How many do you actually expect to have? — Alnitak
– Alnitak, Commented Dec 22, 2011 at 21:49
How is it inneficient? Do you mean inneficient to program since you have to type all the new MyClass or do you think it's doing to much work at runtime? — Daniel Moses
– Daniel Moses, Commented Dec 22, 2011 at 21:50
Why you consider the first as efficient and the second as inefficient? — Sleiman Jneidi
– Sleiman Jneidi, Commented Dec 22, 2011 at 21:53
Do you really mean "empty constructor"? Or a default (or parameter less) constructor. That's kind of confusing. — Bhesh Gurung
– Bhesh Gurung, Commented Dec 22, 2011 at 21:55

Alnitak · Accepted Answer · 2011-12-22 21:50:38Z

6

You either have to write them out one at a time, or you have to use a loop:

MyClass[] myArray = new MyClass[n];
for (int i = 0; i < myArray.length; ++i) {
    myArray[i] = new MyClass();
}

answered Dec 22, 2011 at 21:50

Alnitak

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Mike Adler · Accepted Answer · 2011-12-22 22:12:02Z

0

public static <T> T[] getArray(final Class<? extends T> memberclass, final int numberOfItems) {

    final T[] array = new T[numberOfItems];
    final Constructor constr = memberclass.getConstructor(null);
    for (int index = 0; index < numberOfItems; index++) {
        array[index] = constr.newInstance(null);
    }

    return array;
}

This would a rough draft for a generic method that you can use for that purpose. Of course, I skipped all the exception handling, so this method would bloat a bit more in reality.

answered Dec 22, 2011 at 22:12

Mike Adler

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