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

[Sathish Kumar Thiyagarajan]

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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