Java: Issue with classes

Question

I have following code

class Demo {
    static int a = 0;
    static int b = 1;
    static {
        a = ++b;
    }

    void gam(int x) {
        a = a * x;
        b = b * x;
    }
}

class Test {
    public static void main(String[] args) {
        Demo d1 = new Demo();
        Demo d2 = new Demo();
        d1.a++;
        d2.a--;
        System.out.println(d1.a + " " + d1.b + " " + d2.a + " " + d2.b);
    }
}

But I can't figure out why d1.a is 2. Shouldn't it be 3? Since a=++b makes it 2 and d1.a++ makes it 3?

rgettman · Accepted Answer · 2014-02-03 19:12:28Z

10

The variable a is static, so there is only one a for all instances of Demo. It starts off as 0, and the static initializer sets it to ++b, or 2. Then, d1.a++ increments it to 3, but d2.a-- decrements the same a back down to 2.

answered Feb 3, 2014 at 19:12

rgettman

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Comments

David Cain · Accepted Answer · 2014-02-03 19:46:49Z

0

d1.a is a static member field, so it should be accessed not via the instance. It should accessed via: Demo.a.

And by the way, d1.a and d2.a refer to the same static member field, so the increment of a in d1.a++ is "roll-backed" with the decrement: d2.a--.

edited Feb 3, 2014 at 19:46

David Cain

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answered Feb 3, 2014 at 19:24

Serdal Kaya

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