Reg: Proposal: Generalized Number.parseNumber(String) Method for Java

[Kevin Bourrillion]

I appreciate you raising this; I think it is relevant to some internal discussions we’re having about the future of Number. Here’s some personal reactions from a team member (not a team consensus opinion):

Unfortunately, we’ve found many times that `Number` is a pretty deficient return type that users can’t do much of anything useful with (except apply arbitrarily lossy conversions to, or test with `instanceof`).

And I’m skeptical that most users ever want to end up in a situation where they have a `Number[]` or `Collection<Number>` that could be heterogeneous. This state feels like a temporary one you want to get out of.

It’s not clear that `Number` can really be rehabilitated much, either. It is sort of a “deficient type” by its nature.

When you do need this sort of flexible parsing, I think the status quo is: you can always parse to BigDecimal first, then ask questions about what more “minimal” type the value you got might fit into. Obviously this does not have optimal performance, but I am not sure there’s a good spot-fix here that doesn’t just raise more issues than it tried to resolve.

We will keep thinking about this, though. Valhalla means we will inevitably have more "numeric types" than ever, and this is prompting us to think about what these types should have in common. (It’s a big topic and I apologize for not even attempting to outline it all for you here yet.)



On Mar 28, 2025, at 10:29 AM, Sathish Kumar Thiyagarajan <sathishkumar.thiyagarajan at gmail.com> wrote:


Dear Core-Libs Dev Team,

Note: I have now subscribed to the mailing list and am resending this message as advised.

I would like to propose an improvement to the JDK: a generalized Number.parseNumber(String) method.

Motivation

Java provides multiple number types (byte, short, int, long, etc.), and developers typically choose them based on memory considerations. Currently, Java offers String to Number conversions using concrete classes:

  *   Long.parseLong(String)

  *   Integer.parseInt(String)

  *   Short.parseShort(String), etc.

While these are useful, Java lacks a generalized method that returns the most memory-efficient Number representation based on the input, like:

Number.parseNumber(String numberAsText);


Use Case: JSON Serialization

This would be particularly useful in cases like JSON serialization in REST APIs (Using Jackson<https://github.com/FasterXML/jackson>), where number types are often altered during serialization/deserialization. Consider the following test case:

@Test
void testNumberMemoryUsage() throws JsonProcessingException {
    ObjectMapper mapper = new ObjectMapper();
    Map<String, Object> numbersObject = Map.of("aShort", (short) 1234, "aFloat", (float) 1.33);

    final String jsonText = mapper.writeValueAsString(numbersObject);
    Map<String, Object> parsedJsonObject = mapper.readValue(jsonText, new TypeReference<>() {});

    // Expected: Short.class | Actual: Integer.class
    assertEquals(Short.class, parsedJsonObject.get("aShort").getClass());

    // Expected: Float.class | Actual: Double.class
    assertEquals(Float.class, parsedJsonObject.get("aFloat").getClass());
}


Reference Implementation

Here’s a rough implementation to illustrate the idea:

private static Number parseNumber(final String numberStr) {
    try {
        if (numberStr.contains(".")) {
            double doubleValue = Double.parseDouble(numberStr);
            return (doubleValue >= -Float.MAX_VALUE && doubleValue <= Float.MAX_VALUE) ?
                   (float) doubleValue : doubleValue;
        } else {
            long longValue = Long.parseLong(numberStr);
            if (longValue >= Byte.MIN_VALUE && longValue <= Byte.MAX_VALUE) {
                return (byte) longValue;
            } else if (longValue >= Short.MIN_VALUE && longValue <= Short.MAX_VALUE) {
                return (short) longValue;
            } else if (longValue >= Integer.MIN_VALUE && longValue <= Integer.MAX_VALUE) {
                return (int) longValue;
            } else {
                return longValue;
            }
        }
    } catch (NumberFormatException e) {
        return parseBigNumber(numberStr);
    }
}

private static Number parseBigNumber(final String numberStr) {
    try {
        return new BigInteger(numberStr); // Try BigInteger first
    } catch (NumberFormatException e) {
        // Only create BigDecimal if BigInteger fails
        BigDecimal bd = new BigDecimal(numberStr);
        try {
            // Convert to BigInteger if there's no fraction
            return bd.toBigIntegerExact();
        } catch (ArithmeticException ex) {
            return bd; // If it's a decimal, return BigDecimal
        }
    }
}


Would love to hear your thoughts on this proposal. Appreciate your feedback and guidance!

Thanks & Regards,
Sathish Kumar Thiyagarajan

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