CODEWITHSUNDEEP
java
Modfoo
Modfoo

Reputation: 97

Java - Get value of attribute in a class

Suppose this piece of code:

public class Int {
    public int value;

    public Int () {
        this.value = 0;
    }

    public Int (int value) {
        this.value = value;
    }

    @Override
    public String toString () {
        return Integer.valueOf (this.value).toString ();
    }
}

Using a public attribute, I can access to the value of the attribute using:

Int a = new Int ();
int x = a.value;

I want to ask if there is a way to make this:

Int a = new Int (3);
Int b = new Int (11);

int x = a + b;

instead of:

...
int x = a.value + b.value;

EDIT

Sorry, mea culpa! I know that Java does not support operator overloading. I wrote bad examples.

Int a = new Int (12);
int x = a.value;

There is a way where I can write the code above in this way?

Int a = new Int (12);
int x = a;

So, what I'm asking is if it's possible to access to a specific attribute of a class omitting the name of the attribute.

Upvotes: 0

Views: 120

Answers (2)

Jesper
Jesper

Reputation: 206796

Besides the fact that Java does not support user-specified operator overloading, there is also no mechanism to do auto-(un)boxing with your own classes.

Auto-(un)boxing only works with the 8 standard wrapper classes (Boolean, Byte, Short, Character, Integer, Long, Float and Double) as defined in paragraph 5.1.7 and 5.1.8 of the Java Language Specification.

So there is no way to make this work:

// Your own class Int
class Int { ... }

Int x = new Int(12);
int y = x; // auto-unboxing, not possible with Int

Upvotes: 1

Olivier Croisier
Olivier Croisier

Reputation: 6149

Java does not allow operator overloading (except fot Strings), so the + operator cannot be used to "add" custom classes like your Int.

Which means that, in your case, you cannot use the + operator to do Int x = a + b;.

The correct way to do this in an Object-Oriented language like Java, would be to add a plus (or add) method to you Int class to perform this operation : 

public Int plus(Int other) {
    return new Int(this.value + other.value);
}

EDIT : to answer your new question...

The answer is still no, you can't define custom boxing/unboxing rules. The compiler will compare the type of the reference (int) to the type of the instance (the custom Int class), find they are not in the same hierarchy, and emit a compilation error.

The rules that allow the Number wrappers (Integer, Long, etc.) to be seamlessly transformed to/from primitive types are special exceptions documented in the Java Language Specification.

Upvotes: 0

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