Number Parsing in Java

Our program demonstrates parsing numbers from strings, which is a basic but common task in many programs. Here’s how to do it in Java:

import java.text.ParseException;

public class NumberParsing {
    public static void main(String[] args) {
        // With Double.parseDouble, we don't need to specify precision
        double f = Double.parseDouble("1.234");
        System.out.println(f);

        // For Integer.parseInt, we don't need to specify the bit size
        int i = Integer.parseInt("123");
        System.out.println(i);

        // Integer.parseInt can recognize hex-formatted numbers with a radix of 16
        int d = Integer.parseInt("1c8", 16);
        System.out.println(d);

        // For parsing unsigned integers, we can use Integer.parseUnsignedInt
        long u = Integer.parseUnsignedInt("789");
        System.out.println(u);

        // Integer.parseInt is the equivalent of Atoi for base-10 int parsing
        int k = Integer.parseInt("135");
        System.out.println(k);

        // Parse methods throw NumberFormatException on bad input
        try {
            Integer.parseInt("wat");
        } catch (NumberFormatException e) {
            System.out.println(e.getMessage());
        }
    }
}

Here’s a breakdown of the code:

We use Double.parseDouble() to parse floating-point numbers. Unlike in the original example, Java doesn’t require specifying the precision.
Integer.parseInt() is used for parsing integers. We don’t need to specify the base (it’s assumed to be 10) or the bit size.
For parsing hexadecimal numbers, we use Integer.parseInt() with a radix of 16.
Java doesn’t have a direct equivalent to ParseUint, but we can use Integer.parseUnsignedInt() which returns a long to accommodate larger values.
Integer.parseInt() serves the same purpose as Atoi for basic base-10 integer parsing.
In Java, parse methods throw a NumberFormatException on bad input, which we catch and print.

When you run this program, you should see output similar to this:

1.234
123
456
789
135
For input string: "wat"

Next, we’ll look at another common parsing task: URLs.

Writing Files in Java

Url Parsing in Java

Learn X By Example

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Number Parsing in Java