Java invokes String.valueOf(char[] data) instead of String.valueOf(int i) for Integer parameter and throw ClassCastException

Question

I have a problem with invoking String.valueOf method. As argument I passed generic method which returns Integer type. And then exception is thrown because program try to cast that returned Integer to char[] to invoke String.valueOf method. As I know String has overloaded valueOf() method and one of them can take Integer parameter.

Below is screenshot from Eclipse expression evaluation which shows situation.

This line throws ClassCastException

String quality = String.valueOf(model.get(property));

This is what model.get(property) invokes:

public <X> X get(String property) {
        X value = null;
        try {
            if (allowNestedValues && NestedModelUtil.isNestedProperty(property)) {
                return (X) NestedModelUtil.getNestedValue(this, property);
            }
            if (map != null) {
                Object objValue = map.get(property);
                if (objValue != null)
                    value = (X) objValue;
            }
        } catch (Exception e) {
        }
        return map == null ? null : value;
    }

EDIT:

I added this condition and compiler goes inside the if statement

if(model.get(property) instanceof Integer)
{
    quality = String.valueOf(model.get(property));
}

Stop describing your code, show your code. And post the stacktrace. — luk2302
– luk2302, Commented Jan 21, 2019 at 14:59
Can you edit your question and add a minimal reproducible example of code which reproduces this exception? — Radiodef
– Radiodef, Commented Jan 21, 2019 at 15:00
How do you expect the Java compiler to correctly infer which String.valueOf variant to use? — Mark Rotteveel
– Mark Rotteveel, Commented Jan 21, 2019 at 15:03
@MarkRotteveel then how Java compiler know that it is Integer instance ? — Rafał Sokalski
– Rafał Sokalski, Commented Jan 21, 2019 at 15:04
valueOf has overloads for Object, char[] and various primitive types. char[] is the "most specific" one and is therefore chosen (presumably). — luk2302
– luk2302, Commented Jan 21, 2019 at 15:18

luk2302 · Accepted Answer · 2019-01-21 15:03:41Z

2

How is the compiler supposed to infer the correct X the way you call it?

Split it into

YourType qualityRaw = model.get(property);
String quality = String.valueOf(qualityRaw);

answered Jan 21, 2019 at 15:03

luk2302

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5 Comments

Mark Rotteveel Over a year ago

Doing String.valueOf(model.<YourType>get(property) might also work.

Rafał Sokalski Over a year ago

Why instanceof Integer returns true ?

Rafał Sokalski Over a year ago

Check attached screenshot where instanceof is evaluated and value is true

Mark Rotteveel Over a year ago

@RafałSokalski You are confusing runtime types with compile time inferred types. Method resolution is done at compile time, and here that inferrence turns out to be wrong which results in a runtime class cast exception.

Rafał Sokalski Over a year ago

@luk2302 Thank you

user2963757 · Accepted Answer · 2019-01-21 15:06:07Z

1

You should try Integer.toString method if you know that your return type is of Integer type.

answered Jan 21, 2019 at 15:06

user2963757

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