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

[Volkan Yazıcı]

Sathish, would you mind elaborating on your use case a bit more, please?
That is, I am not able to see where and how you want to leverage
`Number#parseNumber(String)` in the `testNumberMemoryUsage()` method.
Example: *"I have this test method verifying this behavior of that
application. Given a `Number#parseNumber(String)`, I can improve this as
follows."*

On Fri, Mar 28, 2025 at 6:31 PM 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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