Overload Java Data Field Type by Another Field Type

Question

Is it possible to overload a field type to be another field type?

If so, would it be possible to provide some examples?

why don't you go try it out and see what happens. – Sam I am says Reinstate Monica Jul 13 '12 at 16:05 — Sam I am says Reinstate Monica, Jul 13 '12 at 16:05

score 7 · Accepted Answer · edited May 23 '17 at 12:06

7

You can't overload fields (only methods can be overloaded), you might be confused with overriding fields - which anyway is not possible, you end up hiding the fields from superclasses. Take a look at this post.

edited May 23 '17 at 12:06

Community

1
1

answered Jul 13 '12 at 16:05

Óscar López

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I thought this was the case and I was bit confused at first when they came to me about it. I have only been programming Java for three years now and have not came across this. Just wanted to make sure I wasn't missing anything. – Brandon Wilson Jul 13 '12 at 16:14
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@BrandonWilson it is not possible – Pooya Jul 13 '12 at 16:35

score 0 · Answer 2 · answered Jul 13 '12 at 16:07

0

I believe that java supports interfaces, and interfaces should be able to help you achieve what you're trying to achieve

here's an example i found quick

here's a tutorial

just make sure that you're not overloading public members that way.

answered Jul 13 '12 at 16:07

Sam I am says Reinstate Monica

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score 0 · Answer 3 · answered Jul 13 '12 at 16:38

look at this code

class A<T> {
    protected T field1;
}

class B extends A<String> {
    public char field1;

    public static void main(String[] args) {
        A a = new B();
        a.field1 = 12442;
    }
}

it runs without any exception, if field1 overrided, it should raise an exception, but it doesn't

and also this runs without any exception

class A<T> {
    protected T field1;
}

class B extends A<Character> {
    public char field1;

    public static void main(String[] args) {
        A a = new B();
        a.field1 = 12442;
    }
}

It's impossible

score 0 · Answer 4 · edited May 23 '17 at 10:26

The Java language (JLS) does not allow it, but Java bytecode (JVMS) does

Oracle JDK 1.8.0_45 even relies on it to implement assert. For example:

public class Assert {
    static final int[] $assertionsDisabled = new int[0];
    public static void main(String[] args) {
        System.out.println(int.length);
        assert System.currentTimeMillis() == 0L;
    }
}

generates two Oracle JDK 1.8.0_45, one explicit (int[]) and one synthetic (bool), and is happily able to distinguish between them. But if we had declared:

static final boolean $assertionsDisabled = false;

it would fail to compile with:

the symbol $assertionsDisabled conflicts with a compile synthesized symbo

See https://stackoverflow.com/a/31355548/895245 for more details.

Possible rationale why it's not possible

The problem is that it would not be possible to determine the type of the field. Consider:

void f(int i) { System.out.println("int"); }
void f(float i) { System.out.println("float"); }
int i;
float i;
// Which overridden method is called?
void m() { f(i); }

Overload Java Data Field Type by Another Field Type

4 Answers4