Try Parse Multiple Types

Question

I am trying to write a method that takes in a String and returns an Object. The catch is I want to parse it to one of a few different data-types, and if that fails, return the original String. I currently have the code below. Is this the best way to handle what I want or is there something obvious that I'm missing?

private static Object tryParse(String str) {
    try {
        return Long.parseLong(str);
    } catch (NumberFormatException ex1) {
        try {
            return Double.parseDouble(str);
        } catch (NumberFormatException ex2) {
            return str;
        }
    }
}

EDIT: I made a tweak that I think should improve performance a bit since I only need to check for longs, doubles, and Strings.

private static Object tryParse(String str) {
    try {
        Double d = Double.parseDouble(str);
        if (d % 1 == 0) {
            return d.longValue();
        }
        return d;
    } catch (NumberFormatException ex1) {
        return str;
    }
}

Answer 1

Your second code, while might be slightly more efficient than the first due to the avoidance of the second try ... catch inside the first, has two bugs:

First, if str contains a value greater than \$2^{63}-1\$ or less than \$-2^{63}\$, while it is an integer value (d % 1 == 0 will be true), it cannot be expressed as a long, so d.longValue() will discard the upper bits.

Second, if str contains a value which can be parsed as a Long, but has a magnitude greater than \$2^{52}\$, parsing it as a Double will discard some of the low-order bits.

jshell> Double d = Double.parseDouble("10000000000000123");
d ==> 1.0000000000000124E16

jshell> d.longValue()
$2 ==> 10000000000000124

jshell> Long.parseLong("10000000000000123");
$3 ==> 10000000000000123

---

The statements return Long.parseLong(str) and return Double.parseDouble(str) may be doing more work than necessary. These methods return a long and a double, respectively, which then need to be auto-boxed into Long and Double. You should instead use Long.valueOf(str) and Double.valueOf(str) which return already boxed values.

---

I would write this code like:

private static Object tryParse(String str) {
    try {
        return Long.valueOf(str);
    } catch (NumberFormatException ex) { /* no-op */ }

    try {
        return Double.valueOf(str);
    } catch (NumberFormatException ex) { /* no-op */ }

    return str;
}

... which avoids the nested try-catch blocks, so can easily be extended to several other types, possibly even looping over a collection of parsers:

private static Object tryParse(String str) {
    for (Parser parser : parsers) { 
        try {
            return parser.valueOf(str);
        } catch (NumberFormatException ex) {
            /* no-op */
        }
    }

    return str;
}

or even

private static Object tryParse(String str) {
    for (Parser parser : parsers) { 
        Optional<Object> value = parser.valueOf(str);
        if (!value.empty()) {
            return value.get();
        }
    }

    return str;
}

Implementation of Parser, and its instances, left as exercise to student.