Question

Simple question. A friend of mind wrote code similar to this one (which is just to explain you my question, it’s not useful at all….)

class Example{
    private int[] tab = new int[10];
    public Example() {
        for(int i = 0 ; i < 10 ; i++)
            tab[i] = (int)(Math.random()*100);
        for(int i = 0 ; i < 10 ; i++)
            System.out.println(tab[i]);
    }
    public static void main(String[] arg) {
        Example ex = new Example();
    }
}

I told him he should put the new inside the constructor

class Example{
    private int[] tab;
    public Example() {
        tab = new int[10];
    ...
}

When he ask me why, I din’t know what to answer : I didn’t have a definite argument other than “it’s better this way”. The way I learn it, you can initialize variables with basic types (int, double…) but for arrays you should do it in the constructor.

So:

• is it really better?
• Are there some good reasons: Convention, style?
• Does it change anything like less/more memory used?

I’m not considering the case where the number of element can vary. It will ALWAYS be 10

Answer 1

• is it really better ?

Not really, IMO.

• is there some good reasons : convention ? style ?

There may be valid reasons for choosing one way over the other is when you have multiple constructors, or when the initial values depend on constructor arguments; e.g.

private int[] tab;

public Example(int size) {
    tab = new int[size];
    for (int i = 0; i < size; i++)
        tab[i] = (int) (Math.random() * 100);
}

or

private int[] tab = new int[10];

public Example(int initial) {
    for (int i = 0; i < 10; i++)
        tab[i] = initial;
}

public Example() {
    for (int i = 0; i < 10; i++)
        tab[i] = (int) (Math.random() * 100);
}

Apart from that (and in your example) there are no general rules about this. It’s a matter of personal taste.

• does it change anything like less/more memory used ?

In your example it will make no difference. In general, there might be a tiny difference in the code size or performance, but it is not worth worrying about.

In short, I don’t think your suggestion to your friend has a rational basis.

The way I learn it, you can initialize variables with basic types (int, double…) but for arrays you should do it in the constructor.

You should unlearn that … or at least recognize that it is just a personal preference.