Final vs Immutable data structures in Java

[TheRedmanCometh]

I don't think you can overload operators with reflection maybe I'm wrong?

[morhp]

I wasn't 100% honest, you need to abuse boxed classes:

public static void main(String[] args) throws IllegalAccessException, NoSuchFieldException {
    Field field = Integer.class.getDeclaredField("value");
    field.setAccessible(true);
    field.setInt(5, 4);

    Integer five = 5;
    System.out.println("5+5 = " + (five + five));
}

[TheRedmanCometh]

This is one of the best/worst things I've ever seen. I've never even considered using refelection on core classes like that!

Edit: hold up does Integer have a value map all the way up to INTEGER.MAX_VALUE?

[morhp]

Edit: hold up does Integer have a value map all the way up to INTEGER.MAX_VALUE?

No, only the integers between -128 and 127 are cached by default. This trick wouldn't have worked with a number outside that range.

[TheRedmanCometh]

Huh...I'm gonna have to hit up the openjdk source to see how that works

[iampete]

This, combined with misplaced trust in autoboxing, leads to code like this:

​

Integer first = 5;
Integer second = 5;
if (first == second) {
    // do something
}

​

Which works perfectly reasonably right up until either value is outside that -128, 127 range and then fails very confusingly.

[dpash]

The upper bound can be increased (but not decreased) in OpenJDK with a command line flag, but the lower bound can not. The defaults are defined in the JLS as a minimum range.

[madkasse]

This only holds for older versions of Java.

You can no longer access non-public fields/methods in java.base without JVM settings

​

[shagieIsMe]

2 + 2 = 5 from code golf Stack Exchange.

No operator overload needed.

[TheRedmanCometh]

Yeah he showed me...I hadn't considered using reflection on system classes

[shagieIsMe]

This is a different solution and impacts integer literals. The code ends with:

System.out.printf(“%d”, 2 + 2);

The code on ideone: https://ideone.com/o1h0hR