Good way to encapsulate Integer.parseInt()

I know that this is quite an old question, but I was looking for a modern solution to solve that issue.

I came up with the following solution:

public static OptionalInt tryParseInt(String string) {
    try {
        return OptionalInt.of(Integer.parseInt(string));
    } catch (NumberFormatException e) {
        return OptionalInt.empty();
    }
}

Usage:

@Test
public void testTryParseIntPositive() {
    // given
    int expected = 5;
    String value = "" + expected;

    // when
    OptionalInt optionalInt = tryParseInt(value);

    // then
    Assert.assertTrue(optionalInt.isPresent());
    Assert.assertEquals(expected, optionalInt.getAsInt());
}

@Test
public void testTryParseIntNegative() {
    // given
    int expected = 5;
    String value = "x" + expected;

    // when
    OptionalInt optionalInt = tryParseInt(value);

    // then
    Assert.assertTrue(optionalInt.isEmpty());
}

If you're using Java 8 or up, you can use a library I just released: https://github.com/robtimus/try-parse. It has support for int, long and boolean that doesn't rely on catching exceptions. Unlike Guava's Ints.tryParse it returns OptionalInt / OptionalLong / Optional, much like in https://stackoverflow.com/a/38451745/1180351 but more efficient.

Maybe someone is looking for a more generic approach, since Java 8 there is the Package java.util.function that allows to define Supplier Functions. You could have a function that takes a supplier and a default value as follows:

public static <T> T tryGetOrDefault(Supplier<T> supplier, T defaultValue) {
    try {
        return supplier.get();
    } catch (Exception e) {
        return defaultValue;
    }
}

With this function, you can execute any parsing method or even other methods that could throw an Exception while ensuring that no Exception can ever be thrown:

Integer i = tryGetOrDefault(() -> Integer.parseInt(stringValue), 0);
Long l = tryGetOrDefault(() -> Long.parseLong(stringValue), 0l);
Double d = tryGetOrDefault(() -> Double.parseDouble(stringValue), 0d);

They way I handle this problem is recursively. For example when reading data from the console:

Java.util.Scanner keyboard = new Java.util.Scanner(System.in);

public int GetMyInt(){
    int ret;
    System.out.print("Give me an Int: ");
    try{
        ret = Integer.parseInt(keyboard.NextLine());

    }
    catch(Exception e){
        System.out.println("\nThere was an error try again.\n");
        ret = GetMyInt();
    }
    return ret;
}

Considering existing answers, I've copy-pasted and enhanced source code of Integer.parseInt to do the job, and my solution

• does not use potentially slow try-catch (unlike Lang 3 NumberUtils),
• does not use regexps which can't catch too big numbers,
• avoids boxing (unlike Guava's Ints.tryParse()),
• does not require any allocations (unlike int[], Box, OptionalInt),
• accepts any CharSequence or a part of it instead of a whole String,
• can use any radix which Integer.parseInt can, i.e. [2,36],
• does not depend on any libraries.

The only downside is that there's no difference between toIntOfDefault("-1", -1) and toIntOrDefault("oops", -1).

public static int toIntOrDefault(CharSequence s, int def) {
    return toIntOrDefault0(s, 0, s.length(), 10, def);
}
public static int toIntOrDefault(CharSequence s, int def, int radix) {
    radixCheck(radix);
    return toIntOrDefault0(s, 0, s.length(), radix, def);
}
public static int toIntOrDefault(CharSequence s, int start, int endExclusive, int def) {
    boundsCheck(start, endExclusive, s.length());
    return toIntOrDefault0(s, start, endExclusive, 10, def);
}
public static int toIntOrDefault(CharSequence s, int start, int endExclusive, int radix, int def) {
    radixCheck(radix);
    boundsCheck(start, endExclusive, s.length());
    return toIntOrDefault0(s, start, endExclusive, radix, def);
}
private static int toIntOrDefault0(CharSequence s, int start, int endExclusive, int radix, int def) {
    if (start == endExclusive) return def; // empty

    boolean negative = false;
    int limit = -Integer.MAX_VALUE;

    char firstChar = s.charAt(start);
    if (firstChar < '0') { // Possible leading "+" or "-"
        if (firstChar == '-') {
            negative = true;
            limit = Integer.MIN_VALUE;
        } else if (firstChar != '+') {
            return def;
        }

        start++;
        // Cannot have lone "+" or "-"
        if (start == endExclusive) return def;
    }
    int multmin = limit / radix;
    int result = 0;
    while (start < endExclusive) {
        // Accumulating negatively avoids surprises near MAX_VALUE
        int digit = Character.digit(s.charAt(start++), radix);
        if (digit < 0 || result < multmin) return def;
        result *= radix;
        if (result < limit + digit) return def;
        result -= digit;
    }
    return negative ? result : -result;
}
private static void radixCheck(int radix) {
    if (radix < Character.MIN_RADIX || radix > Character.MAX_RADIX)
        throw new NumberFormatException(
                "radix=" + radix + " ∉ [" +  Character.MIN_RADIX + "," + Character.MAX_RADIX + "]");
}
private static void boundsCheck(int start, int endExclusive, int len) {
    if (start < 0 || start > len || start > endExclusive)
        throw new IndexOutOfBoundsException("start=" + start + " ∉ [0, min(" + len + ", " + endExclusive + ")]");
    if (endExclusive > len)
        throw new IndexOutOfBoundsException("endExclusive=" + endExclusive + " > s.length=" + len);
}